Two-dimensional carbon nanosheets codoped with N and P species have been successfully synthesized by a template carbonization method coupled with nitrogenization and phosphorylation processes using trisodium citrate dihydrate, melamine, and NH4H2PO4 as C, N, and P sources, respectively. Dopants of N and P species play crucial roles in the determination of carbon porosities and electrochemical performance; notably, increasing the P content can lead to a decrease in the BET surface area together with a corresponding decrease in the electrochemical performance. For instance, regulating the mass ratio between the C source and the N and P sources to 2:1 results in the maximum BET surface area of 1340 m2 g–1, whereas a ratio of 1:2 results in a decreased value of only 47 m2 g–1. Moreover, the mass ratio of 1:1 results in superior electrochemical behaviors, with a maximum energy density that can reach up to 13.3 Wh kg–1. The present synthesis method provides an alternative route for producing N- and P-containing carbon nanostructures with two-dimensional features, serving as excellent electrode materials for energy propagation and storage.

How to massively produce 2D carbon materials remains an interesting issue. In this work, by a template carbonization approach, 2D carbon nanosheets possessing large surface area of 1229 m2 g–1 and high pore volume of 1.66 cm3 g–1 have been synthesized, using sodium stearate as the carbon source and magnesium powder as a hard template. More importantly, dual redox additives KI and anthraquinone-2-sulfonic acid sodium (AQS) are developed for remarkably improving the capacitances; neutral KNO3 electrolyte can synchronously extend the operating voltage window. It is revealed that KI and AQS undergo redox reactions at the positive and negative electrodes, respectively; the operating voltage window can be prolonged up to 1.8 V, larger than the limitation of water (1.23 V). Introducing dual redox additives KI and AQS into KNO3 electrolyte results in a high energy density of 33.81 Wh kg–1. The present strategy that utilizes dual redox additives occurring at the positive and negative electrodes respectively has provided us a simple but effective avenue for highly improving the energy density of supercapacitors.Keywords: Carbon nanosheets; Dual redox additives; Energy density; KNO3 electrolyte;

We herein present a facile but efficient CTAB-assisted solution-phase synthesis and postannealing approach for preparing a series of necklace-like phosphors, including SrAl2O4:Eu2+, Dy3+, CaAl2O4:Eu2+, Dy3+, and BaAl2O4:Eu2+, Dy3+. The as-prepared samples were characterized by means of XRPD, FESEM, TEM, and PL techniques. The experimental results indicate that CTAB plays the crucial role in the formation of needle-like precursors in solution, which are further converted into the final phosphors in a reducing atmosphere of H2/Ar (15% + 85%). To investigate the optical characteristics of the aluminate phosphors, we conducted the excitation, emission, and afterglow decaying measurements at room temperature. It is noteworthy that the aluminate phosphors are so floppy after being calcined at 1300 °C for 5 h, which effectively avoids the traditional crushing of hard phosphor blocks into small particles.

•Synergistic effect exists between Na2MoO4 and KI due to overlapping redox voltage window.•Adjusting the ratio of Na2MoO4 and KI can greatly affect the capacitive behaviors.•The capacitance has remarkably increased by 17.4 times.•A high energy density can reach up to 65.3 Wh kg−1.A dual system of redox additive by incorporating Na2MoO4 and KI into H2SO4 solution has been developed to highly elevate the capacitance of supercapacitors primarily owing to the synergistic effect between them at the superposed redox voltage. Furthermore, the synergistic effect therein is attributed to the formation of complex substance of (MoxIyO4x)n−Cz, which can promote redox reaction of Mon+ and In− at the interface of carbon electrode and electrolyte. On the other hand, many crucial factors mainly including the molar ratio, concentration of redox additive and voltage window strongly determine the final capacitive behaviors. For example, when adding Na2MoO4 and KI into H2SO4 with the same concentration of 0.1 mol L−1, the resultant capacitance has remarkably increased by 17.4 times, compared with the one without any redox additive, at 3 A g−1 in a two-electrode system. What's more, the homologous energy density can reach up to 65.3 Wh kg−1 at the suitable voltage window (0–1 V). Hence, the present synergism of various kinds of redox additives is intriguing and easily extended to other systems, which could highly elevate the capacitive performances of supercapacitors.

•2D carbon nanosheets are obtained by carbonizing thiocarbanilide mixed with Mg(OH)2.•DQ and HQ serve as dual redox additives.•The consecutive redox processes of DQ and HQ are contributed to the capacitive performance.•A high energy density of 21.1 Wh kg−1 is achieved.Using thiocarbanilide and Mg(OH)2 powders as carbon precursor and template, respectively, novel 2D carbon nanosheets with large area have been produced. Next, based on the cooperative effect, 1, 4-dihydroxyanthraquinone (DQ) and hydroquinone (HQ) regarded as efficient dual redox additives have been incorporated into the electrode carbon material and H2SO4 electrolyte, respectively, to largely elevate the capacitive performance of supercapacitors. More importantly, the cooperative effect results from the redox processes of DQ and HQ consecutively occurring in the electrode carbon material and aqueous H2SO4 electrolyte, respectively. Besides, the molar ratio of DQ and HQ exerts a crucial role in the determination of the electrochemical behaviors and eventually the optimum condition is the mass ratio of 1:1 concerning the DQ and porous carbon within solid electrode while retaining the HQ concentration as 20 mmol L−1 in 1 mol L−1 H2SO4 electrolyte. As a result, the maximum specific capacitance is achieved of 239 F g−1 at 3 A g−1, and furthermore the maximum energy density up to 21.1 Wh kg−1 is almost 3.5 times larger than that of the one without introducing any redox additive.

•Nanoporous carbon material is achieved by a template carbonization method.•Pyrocatechol violet can serve as effective redox additive for elevating the capacitance.•The redox additive delivers superior behaviors in H2SO4, KOH and Na2SO4 electrolytes.•The increasing fold of redox additive can reach up to 2.06 in the case of H2SO4.In present work, we demonstrate a simple but effective redox additive of pyrocatechol violet (abbr. PCV) to largely promote the capacitive performances especially when carried out in three different kinds of electrolytes (H2SO4, Na2SO4 and KOH), mostly due to its fast electron and proton transfer occurring in the electrode/electrolyte interface. It reveals that the PCV dosage incorporated into electrolyte plays a crucial role in the determination of capacitive performance. When conducted in a two-electrode system, incorporating 0.06 mol L−1 PCV into 1 mol L−1 H2SO4 can achieve large capacitance up to 200 F g−1, which is almost 2.06 times than the one without the addition of PCV; besides, the corresponding energy density is of 28 Wh kg−1 (also increasing 2 times). What’s more, PCV has been extended as the redox additive in other electrolytes such as Na2SO4 and KOH, and remarkable promotion in capacitance and energy density also occur, well evincing the high efficiency and universal applicability of PCV for the large promotion of supercapacitors’ performances due to its prominent electrochemical reversibility and high solubility.

•N-doped carbon materials are derived from diphenylcarbazide.•Diphenylcarbazide can also serve as novel redox additive.•Incorporating redox additive into electrode is simple but highly effective.•The specific capacitance has been largely improved up to 497.8 F g−1.Nitrogen-doped nanoporous carbon materials have been prepared by a template carbonization method, in which diphenylcarbazide serves as carbon/nitrogen source and Mg(NO3)2·6H2O powder as hard template, respectively. The mass ratio of diphenylcarbazide and Mg(NO3)2·6H2O powder plays a crucial role in determining the pore structures and electrochemical performances. The resulting carbon-2:1 sample displays large BET surface area of 1366 m2 g−1, and high pore volume of 2.18 cm3 g−1. It also exhibits good cycling stability and superior electrochemical behaviors, including high specific capacitance of 323.5 F g−1 at 1 mA cm−2 in a three-electrode system using 6 mol L−1 KOH as electrolyte. More importantly, to further improve the electrochemical performance, different amounts (8, 16 and 24 mg) diphenylcarbazide herein serving as novel redox additive is introduced into the carbon-2:1 system to form the carbon-2:1-8/16/24 electrodes. As a result, the specific capacitances of the carbon-2:1-8/16/24 electrodes at 2 mA cm−2 have been improved up to be 232.7, 344.4 and 497.8 F g−1, respectively, which are 1.02, 1.51, and 2.18 times than that of the pristine system (∼228.8 F g−1). Furthermore, the carbon-2:1-24 also retains high cycling stability as 77.5% after 5000 cycles. The present method of incorporating diphenylcarbazide (redox additive) into carbon system is simple but efficient for large improvement of supercapacitor performances.

In this work, a series of porous carbon materials with hierarchical porosities have been synthesized via a template carbonization method, in which cheap CaCO3 serves as a template and glucose as a carbon precursor. During the carbonization process, CO2 produced by the decomposition of the CaCO3 template can act as an internal activating agent, significantly improving microporosity and mesoporosity. All the carbon materials obtained by regulating the ratio of glucose to CaCO3 exhibit the amorphous features with a low graphitization degree. Among them, the carbon-1:2 sample shows a high BET surface area of up to 818.5 m2 g−1 and a large total pore volume of 1.78 cm3 g−1 as well as a specific capacitance of 107.0 F g−1 at 1 A g−1. In addition, a series of hydroquinone (HQ), p-aminophenol (PAP) and p-nitrophenol (PNP) as novel redox additives that can produce pseudo-capacitances have been added into the KOH electrolyte for promoting the total capacitive performances via redox reactions at the electrode–electrolyte interface. As expected, a 2.5-fold increase in the galvanostatic capacitance of 240.0 F g−1 in the HQ-0.5 electrolyte occurs, compared with the conventional KOH electrolyte. Similarly, the PAP-0.5 electrolyte and the PNP-0.5 electrolyte also show a high specific capacitance of 184.0 F g−1 at 2 A g−1 (156.6 F g−1 at 3 A g−1) and 153.0 F g−1 at 3 A g−1, respectively. Additionally, the three kinds of electrolytes exhibit excellent cyclic stability. The remarkable improvement of supercapacitors is attributed to the quick reversible Faradaic reactions of amine and hydroxyl groups adhering to the phenyl rings, which largely accelerates electron migration and brings additional pseudocapacitive contribution for carbon-based supercapacitors.

In present work, we demonstrate a simple but effective strategy for high-performance supercapacitors by adding the p-nitroaniline (PNA) into an alkaline electrolyte of KOH. PNA possesses a unique molecular structure with the functional groups of –NH2 and –NO2. Besides, both the product of nitro-reduction (–NH2) and intrinsic –NH2 on the benzene ring can lead to the occurrence of Faradaic redox reactions accompanied by the electron/proton transfer in the mixed electrolytes, whose pseudocapacitance can greatly enhance the total capacitance. Furthermore, another effective additive of the dimethylglyoxime (DMG) has been incorporated into carbon materials for further improving the performances of supercapacitors with a PNA + KOH electrolyte. As for the DMG + PNA + KOH system, a galvanostatic capacitance up to 386.1 F g−1 of the DMG-0.15–PNA-0.15 sample at 3 A g−1, which is nearly two times higher than that of the PNA-0.15 sample (183.6 F g−1) in the PNA + KOH system and nearly three-fold capacitance of the carbon-blank (132.3 F g−1) in the KOH system at the same current density. Furthermore, the specific capacitance still can reach up to 260.0 F g−1 even at 40 A g−1 with a 67.4% capacitance retention ratio. Besides, the DMG-0.15–PNA-0.15 sample exhibits an exceptional capacitance retention of 113% after 5000 charge/discharge cycles by virtue of the potential activated process, which clearly reveals the excellent cycling stability. These remarkable enhancements are ascribed to the synergistic effects of novel additives of PNA and DMG.

•A template carbonization method for effectively preparing porous carbon materials.•The carbon material possessing high nitrogen content and excellent pore structure.•Two novel redox additives of MI and AYR for improving the performance.•Redox additives exhibit quick electron transfer and reversible redox reactions.•Pseudo-capacitance contribution comes from amine group and phenolic hydroxyl.In this work, using folic acid as a carbon/nitrogen precursor and Zn(NO3)2·6H2O as the template, largely nitrogenated (12.4%) and highly porous carbon material has been produced by a synchronous template carbonization and nitridation approach. More importantly, two effective redox additives of magneson Ι (MI) and alizarin yellow R (AYR) have been implemented in KOH electrolyte, and, at the electrode-electrolyte interface, quick electron transfers and reversible redox reactions occur, thus resulting in additional pseudocapacitive contribution. It obviously indicates that the concentrations and functional groups including amine/nitro/hydroxyl groups adhering to phenyl ring have exerted crucial roles in the determination of incrementally capacitive behaviors. In the case of MI as redox additive, the M-10 sample delivers a largely improved capacitance of 451 F g−1 at 3 A g−1, compared with the pristine one without any additives (180 F g−1). As for the case of AYR, the resultant A-10 sample's capacitance also has highly elevated up to 405 F g−1. The redox reaction mechanisms have been fully investigated, and in particular, the nitro groups can be reduced into amine in this system. The present MI and AYR substances can serve as effective redox additives for largely improving the capacitive performance of carbon-based supercapacitors.

•Folic acid serves as excellent carbon/nitrogen sources.•Mg(OAc)2·4H2O has been utilized as template for pore formation.•p-Phenylenediamine acts as effective redox additive.•Redox reaction occurs at the electrode–electrolyte interface.In the present work, we have demonstrated a simple but effective template carbonization approach to convert folic acid into highly nitrogenated nanoporous carbon materials, using Mg(OAc)2·4H2O as template. For the C-800/900/1000 samples, the nitrogen contents can reach up to 9.03%, 6.81%, and 6.65%, respectively, and they also deliver large BET surface areas of 1242.2, 1559.1, and 1302.8 m2 g− 1, and high pore volumes of 1.36, 2.26, and 1.44 cm3 g− 1, respectively. On the other hand, it is revealed that the incorporation of p-phenylenediamine as a redox additive into KOH electrolyte has greatly improved the capacitances, mostly due to the occurrence of pseudo-capacitance derived from the redox reaction of p-phenylenediamine at the electrode/electrolyte interface. For instance, the capacitances of the C-900-6/9/12 samples can reach up to 105.1, 232.8, and 317.6 F g− 1 at 5 A g− 1, respectively, and all of which are much higher than that of the pristine C-900 sample (42. F g− 1). Obviously, we have provided a simple but highly efficient approach for the improvement of the supercapacitor capacitance by introducing the p-phenylenediamine into KOH electrolyte, which exhibits the advantages of low cost, easy operation, high efficiency, etc.

•Sb2MoO6, Bi2MoO6, Sb2WO6, Bi2WO6 are controllably prepared.•Dosage of NaOH in solution plays crucial role in determining the products.•Orthorhombic Sb2O3 and tetragonal Bi12O17Cl2 also occur.•Bi2WO6 and Bi2MoO6 are doped with Eu3+ ions to prepare red phosphors.Under hydrothermal conditions, a series of flake-like Sb2MoO6, Bi2MoO6, Sb2WO6, Bi2WO6 with the Aurivillius structure have been prepared controllably. It reveals that the initial molar ratios of SbCl3-to-NaOH (or BiCl3-to-NaOH) in the reaction system (SbCl3-Na2MoO4, BiCl3-Na2MoO4, SbCl3-Na2WO4, and BiCl3-Na2WO4) play important roles in the determination of product phases. Besides, properly changing the content of NaOH involved can produce some unexpected phases such as orthorhombic Sb2O3 and tetragonal Bi12O17Cl2. Moreover, substituting Bi3+ with Eu3+ at the A site is readily carried out because of their same valence states together with the similar ion radii. Consequently, the as-prepared Bi2WO6 and Bi2MoO6 samples have been doped with Eu3+ ions also under hydrothermal conditions to prepare the phosphors, which possess excellent red characteristics in terms of excitation and emission measurement. The present synthesis protocol has opened up an intriguing but effective avenue for producing antimony/bismuth-based materials, also exhibiting the potential application of red phosphors.

•Magnesium citrate and nickel nitrate as carbon source and graphitization catalyst.•Synchronous carbonization and graphitization method is simple and effective.•Adding redox additive of p-nitroaniline can highly improve the performance.•Redox additive into KOH electrolyte can be operated at ambient condition.Highly nanoporous carbon materials have been produced by a synchronous carbonization/graphitization process, using magnesium citrate serves as the carbon source and nickel nitrate as graphitization catalyst. The carbonization temperature plays a crucial role in determining the porosity and graphitization. The lower temperature favors for the formation of larger porosity, whilst higher temperature for better crystallinity. Resultantly, a high BET surface area of 2587.13 m2 g−1 and large total pore volume of 4.64 cm3 g−1 appear, the case of C-800 sample, thereby resulting in a large specific capacitance of 305.3 F g−1 at 1 A g−1 from the contribution of electric double layer capacitances. More importantly, we demonstrate a novel redox active additive of p-nitroaniline (PNA) into the 6 mol L−1 KOH electrolyte to largely improve the capacitance by the quick self-discharge redox reaction of H+/e−. The C-800-2 sample with the PNA concentration of 2 mmol delivers largely improved capacitance of 502.1 F g−1 at 1 A g−1, which is almost 1.65 fold increase. Apparently, the present PNA is commercially available, and highly effective for elevating the specific capacitance and might be implemented for the wide supercapacitor application.

Nitrogen-doped nanoporous carbon materials with large BET surface area (1322.5 m2 g−1) and pore volume (0.87 cm3 g−1) have been achieved by a synchronous carbonization/nitridation process, simply using potassium biphthalate and azodicarbonamide as carbon/nitrogen sources, respectively. The above carbon materials have been further impregnated with MnOx nanocrystallites that comes from the thermal decomposition of Mn(NO3)2. Taking the carbon-2:1-Mn sample as an excellent example, it also has large BET surface area (1160.1 m2 g−1) and pore volume (0.77 cm3 g−1) and exhibits high nitrogen/manganese contents of 4.13%, and 3.30%, respectively. The carbon-2:1-Mn sample delivers excellent capacitances of 564.5 and 496.8 F g−1 at the current density of 0.5 and 1.0 A g−1, respectively, as well as superior cycling stability of 96.10% even after charging/discharging for 5000 times. The present method of incorporating cheap MnOx substance into carbon matrix is efficient and also easy for large scale production of carbon nanocomposites, especially possessing large BET surface area and high pore volume.

In this work, nitrogen-containing nanoporous carbon with spherical network structure have been prepared using a template carbonization method, in which diphenylguanidine serves as carbon precursor, commercially available CaCO3 as template, and azodicarbonamide as nitridation agent. All the obtained carbon materials exhibit the amorphous features with low graphitization degree. Besides, the nanoporous carbon materials show nanoscale spherical structures, probably due to the spherical structure of the CaCO3. The Carbon-DC sample exhibit a specific surface area of 652.3 m2 g−1, and a specific capacitance of 176.2 F g−1 at a current density of 1 A g−1. Furthermore, the addition of azodicarbonamide which provide both carbon and nitrogen source can effectively tailor the properties of nanoporous carbon. The obtained Carbon-DCA sample contains as high as 12.45 at% of nitrogen has a specific surface areas of 1022.6 m2 g−1. As a result of the nitrogen content increased, the electrochemical performance is also significantly improved, with high specific capacitance (220 F g−1 in 6 M KOH, 263 F g−1 in 1 M H2SO4) and excellent cycling stability after 5000 charge/discharge cycles. This template method provides a simple and inexpensive route to achieve nanoporous carbon for supercapacitor.

•Phenidone act as carbon/nitrogen sources for producing nanoporous carbon materials;•Mg(OH)2 template effectively enlarges the porosities of carbon materials;•Introducing azobisformamide can further improve the nitrogen content of carbon;•The N-doped carbon materials deliver superior electrochemical behaviors for supercapacitor applications.In this study, we present a simple but efficient template carbonization method to prepare nitrogen-doped nanoporous carbon material, in which phenidone acts as carbon/nitrogen sources and Mg(OH)2 as hard template. The results indicate that the carbon-1:1 sample is highly disordered with large BET surface area of 1513 m2 g−1, high pore volume of 2.2 cm3 g−1 and nitrogen content of 3.78%. As a result, it exhibits decent electrochemical behaviors, whose specific capacitance reaches up to 202.0 F g−1 when measured at 1  A g−1 in a three-electrode system. Moreover, azodicarbonamide has been introduced in the process of carbonization to further tailor the porosity of nanoporous carbon, named as the carbon-1:1:1 sample. In consequence, its BET surface area has decreased to be 1261 m2 g−1 but the pore volume increased up to 2.8 cm3 g−1, together with the large enhancement of nitrogen content up to 7.05%. Besides, it thus delivers a higher specific capacitance of 281.0 F g−1 at 1 A g−1, mostly due to the incremental content of nitrogen species. The proposed Mg(OH)2-assisted template carbonization method has provided an intriguing synthesis approach for N-doped nanoporous carbons, especially the nitrogen improvement simply by the addition of azodicarbonamide.

•PVC is converted into nanoporous carbon by a template carbonization method in large scale.•Incorporating MnOx into carbon can greatly improve the electrochemical performance.•The carbon material exhibits high pore volume and hierarchical pore size distribution.•A high specific capacitance as 751.5 F g–1 has been achieved in a three-electrode system.We herein demonstrate a rational template carbonization approach to convert waste polyvinyl chloride into nanoporous carbon, in which inexpensive Mg(OH)2 serves as hard template. The carbon-blank sample that is obtained by designating the mass ratio of polyvinyl chloride and Mg(OH)2 as 1:2 at the carbonization temperature of 700 °C is amorphous and highly porous in essence. It also exhibits large BET surface area of 958.6 m2 g−1, high pore volume of 3.56 cm3 g−1, and hierarchical pore size distribution. To further improve the electrochemical performance, various amounts of MnOx nanoparticles are incorporated into the nanoporous carbon by direct redox reaction between carbon-blank sample and KMnO4 solution at 70 °C. Therein, carbon-Mn2 sample (the mass ratio of carbon-blank sample and KMnO4 is 1:1) behaves the optimal electrochemical performance. Though its porosity to some extent decreases, its specific capacitance has greatly elevated up to 751.5 F g−1 at 1.0 A g−1, compared with that of the carbon-blank sample (∼47.8 F g−1). The incremental capacitance of the carbon-Mn2 sample is mostly attributed to the contribution of pseudocapacitance incurred by faradic reaction of MnOx material. The present synthesis method opens up an avenue to properly dispose waste polyvinyl chloride into nanoporous carbon, especially with the promise in supercapacitor application.

•A direct carbonization method has been implemented to produce nanoporous carbon.•Commercially available Mg(OH)2 or Ca(OH)2 powder serves as template, and thiocarbanilide as carbon/nitrogen source.•The mass ratio and the carbonization temperature play crucial roles in determining the pore structures.•Three-electrode system has been adopted to measure the electrochemical behaviors.•The carbon materials deliver superior capacitive performance for supercapacitor applications.A valid and facile template carbonization route for producing nanoporous carbons with hierarchical porosities has been implemented by using thiocarbanilide as carbon/nitrogen precursor, and commercially available Mg(OH)2 or Ca(OH)2 powder as template. This work is to clarify the significance and difference between Mg(OH)2 and Ca(OH)2 being as templates. The mass ratio of thiocarbanilide and Mg(OH)2 or Ca(OH)2, as well as the carbonization temperature plays crucial role in determining the pore structures and the resultant capacitive behaviors. It reveals that carbon-Mg sample whose template is Mg(OH)2 (with a mass ratio of 1:2 at 700 °C) exhibits the amorphous feature with low graphitization degree. Similar result also occurs in the case of the carbon-Ca sample. The carbon-Mg sample presents high specific surface area (1018.48 m2 g−1), large pore volume (5.29 cm3 g−1), while those of the carbon-Ca sample are 429.11 m2 g−1 and 2.52 cm3 g−1, respectively. The carbon-Mg sample delivers a high specific capacitance of 327.4 F g−1 at a current density of 1.0 A g−1, as well as a large energy density of 45.47 Wh kg−1 at a power density of 0.5 kW kg−1 in comparison with carbon-Ca sample of (260.0 F g−1) and (36.11 Wh kg−1). What’s more, the carbon-Mg sample exhibits higher capacitance retention of 95.45% after 10,000 charge/discharge cycles than carbon-Ca sample of 91.62% in 6 mol L−1 KOH electrolyte. Using Ca(OH)2 or Mg(OH)2 as template by a template carbonization route provides a simple but feasible protocol to achieve nanoporous carbons with precisely controlled architecture and hierarchical porosities.

•The zinc citrate serves both as carbon source and template.•Adding ZnCl2 into zinc citrate can further increase the carbon porosity.•The capacitive performance has been largely enhanced by introducing PPD additives.•The specific capacitance can reach up to 934.6 F g−1.In this work, we demonstrate a simple template carbonization method to prepare nanoporous carbon materials, in which zinc citrate serves as carbon source and the ZnO substance together with some gases in situ thermally produced as templates. The resultant carbon-800 sample has a large surface area of 740.5 m2 g−1, and high pore volume of 1.96 cm3 g−1. To further increase the porosity of the above carbon materials, ZnCl2 that can act as activation agent and template has been added into the zinc citrate precursor. As a result, the surface area of the carbon-ZnCl2-800 sample has largely increased up to 1244.2 m2 g−1, and pore volume up to 2.21 cm3 g−1. In a conventional 6 mol L−1 KOH electrolyte, the specific capacitances of the carbon-800 and carbon-ZnCl2-800 samples can reach up to 194.8–335.6 F g−1, respectively, at 2 A g−1. Next, a novel redox active electrolyte of p-phenylenediamine (PPD) with quick reversible Faradaic process at the electrode–electrolyte interface has been introduced into the 6 mol L−1 KOH electrolyte. Remarkably, the specific capacitance of the carbon-ZnCl2-800 sample have reached up to 934.6 F g−1 at 2 A g−1 when designating the PPD concentration as 14 mmol L−1 in 6 mol L−1 KOH electrolyte, which is nearly 2.8 fold higher than the pristine one, clearly indicating the pseudo-capacitive effect of the PPD additive.

•Diphenylcarbazide acts as both carbon source and redox additive.•Electron and proton transfers occur in the redox additive–carbon material system.•Introducing redox additive has highly improved the supercapacitor performance.•Redox additive into KOH electrolyte can be realized at ambient condition.In this work, we demonstrate two kinds of novel redox additives, diphenylcarbazide (abbr. DC) and phenylazoformic acid 2-phenylhydrazide (abbr. PP), with quick and reversible redox reaction incorporated into carbon-based supercapacitors. It is revealed that the 4-electron and 4-proton transfer occurring in the redox additive–carbon material system within the electrode can result in additional capacitance. When introducing 24 mg DC or PP substance into 24 mg carbon system, largely improved specific capacitances of 544.3 or 427.6 F g− 1 are achieved, which are almost 4.31 and 3.39 times, respectively, than that of the pristine carbon (126.1 F g− 1) at the current density of 2 A g− 1. Besides, their corresponding capacitance retentions can reach up to 78.9% and 75.6%, respectively, after 5000 charge–discharge cycles, and both of them are somewhat smaller than that of the pristine carbon (96.8%) due to the incremental electronic resistances. The present commercially available, low-cost and highly effective redox additives of DC and PP are quite promising and expected to be implemented for high performance supercapacitors.

•Azodicarbonamide serves as efficient nitrogen source for N-doped carbon.•A template carbonization method is implemented to produce N-doped porous carbon.•The carbon materials exhibit large surface areas and pore volumes.•The N-doped carbon materials deliver superior electrochemical behaviors for supercapacitor applications.A series of N-doped nanoporous carbons are prepared via a synchronous template carbonization and nitridation method, in which glucose serves as carbon precursor, azodicarbonamide (ADC), urea and melamine as nitridation agents and templates. Results indicate that all the obtained carbon materials deliver the amorphous features with low graphitization degree. The Carbon-G-A sample prepared by heating glucose and ADC at 800 °C exhibits high surface area of 624.8 m2 g−1, large total pore volume of 0.53 cm3 g−1 and fairly high nitrogen content of 10.35%. The Carbon-G-A sample delivers superior electrochemical performance, whose specific capacitance can reach up to 202.7 F g−1 at a current density of 1 A g−1. What’s more, it exhibits long-term cycling ability of 92.3% retention even after 5000 cycles. Besides, in the cases of urea and melamine as nitrogen sources, the resultant nitrogen-containing carbons deliver smaller porosities and lower nitrogen contents, but also acceptable specific capacitances of 148.7 and 126.1 F g−1 at 1 A g−1, respectively. It opens a straightforward and easy protocol to convert inexpensive glucose into highly capacitive nitrogen-doped nanoporous carbon materials, using ADC, urea and melamine as nitrogen sources.

A straightforward multitemplate carbonization method for producing nanoporous carbons has been implemented using magnesium citrate as the carbon source and magnesium powder as the template. Notably, the crystallinities of the carbon materials were greatly enhanced with increasing carbonization temperatures. Sample C-4:1–900 obtained by carbonizing the mixture of magnesium citrate and Mg powder (in a mass ratio of 4:1) at 900 °C exhibited a large BET surface area of 1972.1 m2 g–1 and a high pore volume of 4.78 cm3 g–1, thereby resulting in the best electrochemical behaviors. It delivered a large specific capacitance of 236.5 F g–1 at 1 A g–1 when measured in a three-electrode system. Additionally, in a two-electrode system, the energy density was 15 Wh kg–1 for a power density of 0.5 W kg–1, when measured at an operating temperature of 80 °C.

The nanoporous graphitic carbon materials (NGCM) have been prepared by a synchronous carbonization and graphitization process, using waste polyvinylidene fluoride (PVDF) as carbon precursor and Ni(NO3)2·6H2O as the graphitic catalyst. It reveals that the carbonization temperature plays a crucial role in determining the pore structures as well as their electrochemical performances. Increasing the carbonization temperature from 800 to 1200 °C, the corresponding porosity has slightly decreased, accompanied by an increase of graphitization degree. Next, to further improve the electrochemical performance of the sample prepared at 800 °C, a novel redox additive of 4-(4-nitrophenylazo)-1-naphthol (NPN) with different amounts has been introduced in 2 mol L–1 KOH electrolyte. Therein, the specific capacitance by adding 4 mmol L–1 of NPN can reach 2.98 times higher than the pristine value. Apparently, the mixed electrolytes have largely enhanced the electrochemical performance, which is expected to be applied in the field of high performance supercapacitors.

Producing nanoporous carbons that possess high porosity and superior electrochemical performance is a challenge for scientists. In this work, a simple and efficient template carbonization method, without any physical/chemical activation treatment, has been implemented to produce nanoporous carbons doped with nitrogen species. 4-(4-Nitrophenylazo)resorcinol serves as a carbon/nitrogen source and Mg(OH)2 as a hard template. All resultant carbon samples are amorphous, highly porous in nature and display sheet-like nanostructures. The carbon-1:3-L sample whose precursor is obtained by solution method exhibits better porosity, and larger nitrogen content, than those obtained by solid state method (the carbon-1:3-S sample). The carbon-1:3-L sample exhibits large specific surface area (SBET) of 1427.7 m2 g−1, and high total pore volume (VT) of 5.91 cm3 g−1, whereas those of the carbon-1:3-S sample are of 1036.6 m2 g−1 and 4.76 cm3 g−1, respectively. Notably, the present pore volumes are much higher than most of the previously reported for nanoporous carbons. As a consequence, the carbon-1:3-L sample delivers superior electrochemical behaviors, whose specific capacitance reaches up to 378.5 F g−1 when measured at 1 A g−1 in a three-electrode system, compared with that of 263.4 F g−1 of the carbon-1:3-S sample. The present Mg(OH)2-assisted template carbonization method is simple and easy to operate, indicating its potential application for producing nanoporous carbons.

We present a simple template carbonization method to produce nanoporous carbons in which potassium biphthalate and magnesium powder serve as the carbon source and hard template, respectively. It reveals that increasing the carbonization temperature can lead to an increase in crystallinity but porosity and the resultant electrochemical performance in supercapacitor application also decreases. The carbon-3:1-800 sample that was obtained by carbonizing potassium biphthalate and magnesium powder (mass ratio of 3:1) at 800 °C exhibits the best electrochemical performance. It has the largest BET surface area of 1745.6 m2 g−1 and a high pore volume of 1.46 cm3 g−1. When measured in a three-electrode system, the carbon-3:1-800 sample delivers a large specific capacitance of 234.2 F g−1 at a current density of 1 A g−1 and high capacitance retention of 96.6% even after 10000 cycles. More importantly, the influence of the operation temperature of the carbon-3:1-800 sample on the electrochemical behavior was also investigated in a two-electrode system. The energy density can reach up to 96.9 W h kg−1 in the case of the power density of 1.5 kW kg−1; it also reveals that a higher operation temperature can result in better electrochemical performance, enabling its implementation under extreme circumstances.

In this work, a simple template carbonization method has been developed to produce nitrogen-containing nanoporous carbon from diphenylcarbazide, using Mg(OH)2 as hard template. The carbonization temperature has a crucial role in determining the carbon structure. The carbon-3:1-800 sample obtained with the mass ratio of diphenylcarbazide and Mg(OH)2 as 3:1 at 800 °C exhibits the optimum pore structure as well as the resultant best electrochemical performance. It has a large BET surface area of 1538.0 m2 g−1, high pore volume of 3.48 cm3 g−1, and hierarchical pore size distribution. As a result, it delivers superior electrochemical behaviors in a three-electrode system using 6 mol L−1 KOH as electrolyte, whose specific capacitance calculated from galvanostatic charge-discharge curve can reach up to 517.4 F g−1 at a current density of 1 A g−1, which is much larger than most of the nanocarbons ever reported in the literature. The carbon-3:1-800 sample also exhibits good cycling stability within 10000 cycles. Comparatively, the electrochemical test has also been carried out in a two-electrode system using [EMIm]BF4/AN as electrolyte. More importantly, the operation temperatures of 25/50/80 °C can greatly broaden the application scope of nanoporous carbon in the supercapacitor.

A rational template carbonization method has been implemented to produce nanoporous carbon as high performance supercapacitor electrode material. Sodium carboxymethyl cellulose (NaCMC) acts as carbon source, and inexpensive Mg(OAc)2·4H2O and Zn(OAc)2·2H2O as templates. It reveals that the carbonization temperature and the mass ratio of NaCMC, Mg(OAc)2·4H2O and Zn(OAc)2·2H2O are crucial for determining the carbon structure. The NaCMC-Mg-Zn-1:5:0.5 sample displays highly porous structure with large surface area (1596 m2 g−1), pore volume (5.93 cm3 g−1) and hierarchical pore size distribution. The carbon sample is measured in a two/three-electrode system, respectively. It has a high specific capacitance of 428.4 F g−1 at 1 A g−1, together with nice cycling durability. A high energy density up to 68.6 Wh kg−1 can be achieved as the power density of 1.5 kW kg−1. The templates used in this work are cheap, commercially available and this template carbonization method, especially without any activation process, can be readily extended to prepare other kinds of nanoporous carbon.

•A direct carbonization method has been developed to prepare nanoporous carbon.•Potassium biphthalate, zinc, magnesium, and aluminum metals are commercial available.•The carbons have large BET surface areas and high total pore volumes.•Two-electrode system and three-electrode system were implemented.A simple but efficient template carbonization method has been implemented for the production of highly nanoporous carbon by the reaction of potassium biphthalate with zinc, magnesium, or aluminum metal. The mass ratio and carbonization temperature are pivotal factors influencing the structures of the carbons. It explicitly reveals that the carbons produced in the potassium biphthalate-zinc metal system exhibit superior porosities and better electrochemical performances. Taking the Zn-3:1-900 sample as an example, it has a large BET surface area of 1605.1 m2 g−1 and a high total pore volume of 1.18 cm3 g−1. A large specific capacitance of 338.2 F g−1 is achieved at a current density of 1 A g−1 and it can retain a 100.5 F g−1 even at a high current density up to 100 A g−1 when measured in a three-electrode system. It also exhibits a high energy density of 76.7 Wh kg−1 obtained in a two-electrode system. Furthermore, in the two kinds of electrode systems, all of the carbons display excellent cycling stabilities.

High performance porous carbons for supercapacitors have been successfully prepared through a template carbonization process with the help of magnesium acetate, using a zinc salicylate complex as a carbon source. The carbon–Zn–Mg-900 sample has amorphous features and a developed porous structure. Note that it has a high BET surface area of 2008 m2 g−1, a large pore volume of 3.44 cm3 g−1 and a rationally hierarchical pore size distribution. In a three-electrode system using 6 mol L−1 KOH as the electrolyte, it displays a high specific capacitance of 288.3 F g−1 at 1 A g−1, as well as a good rate capability and long term cycling durability (the retention is 96.6% after cycling 10000 times). Furthermore, in a two-electrode system using [EMIm]BF4/AN as a mixed electrolyte, it reveals that operation temperatures of 25, 50, and 80 °C can greatly influence the electrochemical behavior. Higher operation temperatures can usually result in a better electrochemical performance. The measurements in a two-electrode system especially at different operation temperatures can, to a large extent, amplify the application scope of practical supercapacitors.

•A direct carbonization method has been adopted to produce porous carbon.•Flake-like aluminium salicylate coordination polymer is used as precursor.•The surface areas and pore structures of porous carbon can be simply tuned.•The carbon sample exhibits excellent electrochemical performance.Flake-like nanoporous carbon has been synthesized by the direct carbonization of aluminium salicylate coordination polymer that serves as hard templates and carbon sources. It reveals that the carbonization temperature plays a crucial role in the formation of nanoporous carbon. The correlation between specific surface areas, pore structures, surface functionalities and capacitive performances are investigated. The nanoporous carbon synthesized at 900 °C, named as carbon-900, exhibits high surface area of 1162 m2 g−1 and large total pore volume of 0.80 cm3 g−1. The electrochemical behaviors are measured in a three-electrode system. In details, high specific capacitance of 220.0 F g−1 is achieved at a current density of 0.5 A g−1, whereas it also delivers high energy density of 30.5 W h kg−1, and long cycle stability (∼88.57% retention after 3000 cycles).

Halogen-containing plastic materials have been converted into nanoporous carbon by a template carbonization method, using zinc powder as an efficient hard template. The mass ratio between plastics and zinc powder as well as carbonization temperature plays a crucial role in determining the carbon structures and resultant electrochemical performances. The PTFE-1:3-700 sample that is obtained by carbonizing polytetrafluoroethene and zinc powder (the mass ratio of 1:3) at 700 °C has a large BET surface area of 800.5 m2 g–1 and a high total pore volume of 1.59 cm3 g–1, also delivering excellent specific capacitance of 313.7 F g–1 at 0.5 A g–1. Moreover, it exhibits a superior cycling stability with high capacitance retention of 93.10% after cycling for 5000 times. More importantly, it can be extended to produce nanoporous carbon derived from other halogen-containing plastic materials such as poly(vinylidene fluoride) and poly(vinyl chloride), revealing the generality of the synthesis method.

Porous carbons have been synthesized by a direct carbonization of potassium biphthalate without an activation process. The experimental results demonstrate that the carbonization temperature plays a crucial role in determining the surface area and pore structure as well as the correlative capacitive performance. The carbon-700/800/900 samples display surface areas of 672, 1,023, and 1,380 m2 g−1 and total pore volumes of 0.38, 0.56, and 0.78 cm3 g−1, respectively. The specific capacitances of the carbon-700/800/900 samples are 300.4, 272.3, and 243.4 F g−1, respectively, at a current density of 0.5 A g−1. More importantly, the carbon-900 sample possesses the highest capacitance retention (~98.4 %) even undergoing charge–discharge 10,000 times. The potassium biphthalate used as a carbon source is inexpensive and commercially available, making it promising for the large-scale production of porous carbons as an excellent electrode material for supercapacitors.

We demonstrate a rational template carbonization method to produce nitrogen-containing nanoporous carbons at 800 °C, using 1, 10-phenanthroline (or benzimidazole) as carbon/nitrogen source and magnesium citrate as template. The mass ratio of 1, 10-phenanthroline (or benzimidazole) and magnesium citrate has exerted the vital role in the determination of pore structures and the resulting electrochemical performances. It reveals that the carbon-P:Mg-1:1 (obtained by heating 1, 10-phenanthroline and magnesium citrate at 800 °C with the mass ratio of 1:1) and carbon-B:Mg-1:1 (obtained by heating benzimidazole and magnesium citrate at 800 °C with the mass ratio of 1:1) samples both are amorphous, nitrogen-containing, and highly nanoporous in nature. The carbon-P:Mg-1:1 sample has a large BET surface area of 1,657.4 m2 g−1 and high pore volume of 1.83 cm3 g−1, and those of carbon-B:Mg-1:1 sample are of 1,105.4 m2 g−1 and 1.67 cm3 g−1, respectively. Based on a three-electrode system using a 6-mol L−1 KOH aqueous solution as electrolyte, the carbon-P:Mg-1:1 and carbon-B:Mg-1:1 samples can deliver large specific capacitances of 289.0 and 255.6 F g−1 at a current density of 0.5 A g−1. They can also exhibit high energy densities of 40.1 and 35.5 Wh kg−1 when designated the power density as 0.25 kW kg−1 as well as highly long-term cycling durabilities.

In this work, we demonstrate a novel and general synthetic approach for producing nanoporous carbon materials, using adipic acid and zinc powder as raw materials. The mass ratio and carbonization temperature have crucial effects on the structure and electrochemical behavior of the carbon samples. The optimum sample is carbon-1:2-700; it is amorphous in nature and has a high BET surface area of 1426 m2 g−1 and a very large pore volume of 5.92 cm3 g−1. What's more, the sample takes on sheet-like structures entirely composed of nanopores. The electrochemical performance is measured in a three-electrode system using 6 mol L−1 KOH as the electrolyte, and a two-electrode system using [EMIm]BF4/AN as the electrolyte, respectively. In the three-electrode system, it delivers a high specific capacitance of 373.3 F g−1 at a current density of 2 A g−1. Furthermore, it displays a good cycling durability of 93.9% after 10000 cycles. In the two-electrode system, the voltage window has been largely broadened and a series of temperature-dependent measurements are adopted. More importantly, the present synthetic method can be extended to other chemical substances as carbon precursors to produce porous carbon, which can greatly enrich the field of porous carbon synthesis as well as their application as supercapacitors.

High performance nitrogen-doped porous carbon for supercapacitors, named as Gelatin–Mg–Zn-1:5:3, has been successfully prepared via a dual-template carbonization method, without any physical/chemical activation process, in which gelatin serves as both carbon/nitrogen source, and low cost Mg(NO3)2·6H2O and Zn(NO3)2·6H2O as dual templates. It is revealed that the carbonization temperature, and the mass ratio of gelatin–Mg(NO3)2·6H2O–Zn(NO3)2·6H2O plays a crucial role in the determination of surface area, pore structure and the correlative capacitive behavior of the Gelatin–Mg–Zn-1:5:3 sample. It displays a high BET surface area of 1518 m2 g−1, large total pore volume of 4.27 cm3 g−1, and large average pore width of 11.3 nm. In a three electrode system, using 6 mol L−1 KOH solution as electrolyte, we can achieve a high specific capacitance of ca. 284.1 F g−1 at a current density of 1 A g−1 and high capacitance retention of ca. 31.2% is obtained at 150 A g−1, indicating high rate capability. It also possesses a high capacitance retention of ca. 96.1% even after charging/discharging for 10000 cycles. More importantly, a two electrode system, using [EMIm]BF4/AN (weight ratio of 1:1) as electrolyte, has been adopted for the Gelatin–Mg–Zn-1:5:3 sample with different operation temperatures of 25/50/80 °C. As a result, wide voltage windows, broad operation temperatures, and high cycling stability achieved in the two electrode system make it possible for practical application under extreme conditions.

A hard–soft dual templates method has been developed for the first time to prepare porous carbons by the direct carbonization of phenol formaldehyde resins (PFs), Zn(NO3)2·6H2O and polyvinyl butyral (PVB) at 1000 °C under Ar gas, in which PFs serve as the carbon source. More importantly, Zn(NO3)2·6H2O and PVB acting as hard and soft template, respectively, can be readily removed through the evaporation process, resulting in pure carbon without any post-treatment, commonly employed. The PF-Zn-PVB-1:5:1 sample has a total BET surface area of 864 m2 g−1, and a total pore volume of 0.76 cm3 g−1. An electrode based on the porous carbons exhibits the high specific capacitances of 174.7 F g−1 and 152.8 F g−1 at the current densities of 0.5 and 1.0 A g−1, respectively. It also exhibits a superior rate capability, with high specific capacitance retention at ca. 63.1% at a high current density of 20 A g−1. Significantly, about 96.2% is retained after charging and discharging for 10000 cycles, revealing its long-term electrochemical stability. The hard–soft dual templates method proposed in the present work is straightforward and effective, and can be utilized to synthesize porous carbons on a large scale for the application of high performance supercapacitors.

As a generalized synthetic protocol, porous carbons have been for the first time prepared by a direct carbonization of polyacrylate–metal complexes. The case of magnesium polyacrylate was emphatically studied. It reveals that the carbonization temperature can play a crucial role in the determination of surface areas, pore structures, surface functionalities of porous carbons as well as the correlative capacitive performances. The carbon-Mg-900 sample exhibits a high surface area of 942 m2 g−1 and a large total pore volume of 1.90 cm3 g−1, with a high specific capacitance of 262.4 F g−1 at 0.5 A g−1 in 6.0 mol L−1 aqueous KOH electrolyte. Moreover, it displays high capacitance retention even of 33.5% at 100 A g−1, and long-term cycling ability (∼91.3% retention after 5000 cycles). More importantly, the present synthetic strategy can be extended to prepare other polyacrylate–metal complexes, such as calcium polyacrylate and aluminum polyacrylate. The carbon-Al-900 sample can exhibit a high surface area of 1556 m2 g−1 and a large total pore volume of 0.97 cm3 g−1. To sum up, the carbon samples derived from magnesium polyacrylate possess the highest capacitive performances as supercapacitor electrode materials.

•A direct carbonization method was developed for nitrogen-doped porous carbon.•Tartrazine can serve as not only carbon source but also as nitrogen source.•High surface areas and pore volumes are achieved with Ca(OAc)2·H2O.•The carbon samples exhibit excellent capacitive behaviors.Nitrogen-doped porous carbons possessing high surface areas and large pore volumes have been prepared by directly heating the mixture of tartrazine and Ca(OAc)2·H2O at 800 °C especially without further physical or chemical activation, where Ca(OAc)2·H2O serves as the hard template to regulate the surface area and pore structures. It reveals that the addition of Ca(OAc)2·H2O can remarkably improve the surface area and total pore volume. The T-Ca-800-3:1 sample displays the highest BET surface area as 1669 m2 g−1 and largest total pore volume 0.85 cm3 g−1, which is much larger than those without adding Ca(OAc)2·H2O. Furthermore, it exhibits excellent capacitive performances, including high specific capacitance (ca. 224.3 F g−1 at 0.5 A g−1), good rate capability (the retention of 42.6% at 60 A g−1) and good cycling stability (the retention of 92.3% within 5000 cycles).High-performance nitrogen-doped porous carbons have been prepared by directly heating the mixture of tartrazine and Ca(OAc)2·H2O at 800 °C, and the Ca(OAc)2·H2O serves as the hard template.

Nitrogen-doped porous carbon electrodes with remarkable specific capacitance have been fabricated by the rational carbonization of zinc(II)-bis(8-hydroxyquinoline) (abbr. Znq2) coordination polymer, and heating treatment with CO(NH2)2. The experimental results demonstrate that the mass ratio of carbon precursor and CO(NH2)2 plays a key role in the formation of porous carbon with various nitrogen content as well as specific surface areas and pore structures. The cyclic voltammetry and galvanostatic charge–discharge measurements show that the capacitive performance has been remarkably improved by doping with nitrogen. The specific capacitance of 219.2 F g−1 is achieved at the current density of 1 A g−1 with nitrogen-doped porous carbon, increasing up to ca. 56.8% compared to that with pristine porous carbon. The nitrogen-doped porous carbon electrode exhibits enhance capacitance retention as ca. 45.2% at 20 A g−1 as well as cycling stability (ca. 7.6% loss after 3000 cycles). The present carbonization method as well as the nitrogen-doping method for porous carbon from coordination polymer can enrich the strategies for the production of carbon-based electrodes materials in the application of electrochemical capacitors.Graphical abstractHighlights► A simple carbonization method was developed to prepare porous carbon. ► The precursor of Znq2 derives from coordination polymer. ► The doping processes for nitrogen/boron are simple and reproducible. ► Doping nitrogen into carbons can greatly improve capacitive performances.

High-performance porous carbons have been prepared as supercapacitor electrode materials by co-doped with nitrogen and MnOx via a direct carbonization method, using sodium butyl naphthalene sulfonate (abbr. BNS–Na) as carbon source. It is believed that the in situ formed Na6(SO4)2(CO3) in the product would probably serve as temporary template for producing porous structures. The impacts of nitrogen/MnOx contents as well as the structures upon the capacitive performances were emphatically discussed. It indicates that introducing nitrogen and/or MnOx into the carbon matrix can remarkably improve their capacitive performances based on the cyclic voltammetry and galvanostatic charge–discharge measurements in 6 mol L−1 KOH aqueous solution. The specific capacitances of doped carbons can reach up to ca. 167.0–241.8 F g−1 compared with that of the undoped carbon of ca. 105.6 F g−1. Of these samples, the carbon–Mn-1:30-N-1:15 sample co-doped with nitrogen and MnOx exhibits the highest specific capacitance and energy density up to 241.8 F g−1 and 33.6 Wh kg−1, respectively. In particular, these carbons also exhibit high intrinsic capacitances (i.e., capacitance per surface area) up to ca. 0.66–1.92 F m−2.Graphical abstractHighlights► A simple carbonization method was developed to prepare porous carbon. ► The doping processes for nitrogen/MnOx are simple and reproducible. ► Doping nitrogen/MnOx into carbons can greatly improve capacitive performances.

•A simple carbonization method was developed to prepare porous carbon.•The precursor of CMS-Na is cheap and sustainable.•The doping process for nitrogen is simple and reproducible.•Doping nitrogen into carbons can greatly improve capacitive performances.Solid-state method as well as hydrothermal treatment and postannealing method were applied to prepare porous carbons, using sodium carboxymethyl starch (abbr. CMS-Na) as carbon source. The as-prepared carbons were further heated with urea to produce nitrogen-doped carbons. The nitrogen content within carbons has crucial impact on the surface areas, pore structures and capacitive properties. The experimental results reveal that the capacitive performances of nitrogen-doped carbons by solid-state method are much better than those by hydrothermal treatment and postannealing method. Specific capacitance at the current density of 1 A g− 1 of the carbon-S-N-1:20 sample has improved up to 176.0 F g− 1 from 147.2 F g− 1 (carbon-S-blank); the carbon-H-N-1:20 sample has dramatically improved up to 170.3 F g− 1 from 68.3 F g− 1 (carbon-H-blank). Furthermore, the carbon-S-N-1:20 sample exhibits better rate capability, cycling stability, and power density.Solid-state method as well as hydrothermal treatment and postannealing method have been applied to prepare a series of porous carbons doped with nitrogen in a comparative manner, using sodium carboxymethyl starch (abbr. CMS-Na) as carbon source.

Through a simple and convenient template carbonization method, nitrogen-doped porous carbon has been successfully achieved by heating urea formaldehyde (UF) resin and magnesium citrate at 800 °C, where the magnesium citrate serves as a template. The mass ratio between the UF resin and magnesium citrate plays a crucial impact on the surface areas, pore structures, and the correlative capacitive behaviors of the final porous carbons, denoted as samples UF-Mg-1:1, -1:3, and -1:5. All present porous carbons exhibited amorphous features with low graphitization degrees. Sample UF-Mg-1:3 displayed the best capacitive performance with a large specific capacitance of 239.7 F g–1 at a current density of 0.5 A g–1 and a high energy density of 33.3 Wh kg–1 at a power density of 0.25 kW kg–1. More importantly, it exhibited a high capacitance retention of 94.4% after 5000 charge/discharge cycles, clearly indicating good cycling durability.

Spherical nitrogen-doped porous carbons have been prepared through a template carbonization method, in which polyacrylamide (PAM) serves as carbon and nitrogen sources, and calcium acetate as hard template. It reveals that the mass ratio of polyacrylamide and calcium acetate and the carbonization temperature have crucial impacts upon the pore structures and the correlative capacitive performance. The PAM-Ca-650-1:3 sample displays the best capacitance performance. It is amorphous with low-graphitization degree, possessing a total BET surface area of 648 m2 g–1 and total pore volume of 0.59 cm3 g–1. At a current density of 0.5 A g–1, the resultant specific capacitance is 194.7 F g–1. It exhibits high capacitance retention of 97.8% after charging–discharging 5000 times. The polyacrylamide used is cheap and commercially available, making it promising for large-scale production of porous carbons containing nitrogen as an excellent electrode material for supercapacitor.

High-performance porous carbons as supercapacitor electrode materials have been prepared by a simple but efficient template carbonization process, in which commercially available terephthalic acid–zinc complex is used as a carbon source. It reveals that the carbonization temperature plays a crucial role in determining the structure and capacitive performance of carbons. The carbon-1000 sample has high surface area of 1138 m2 g–1 and large pore volume of 1.44 cm3 g–1 as well as rationally hierarchical pore size distribution. In a three-electrode system, the carbon-1000 sample possesses high specific capacitances of 266.0 F g–1 at 0.5 A g–1 and good cycling stability. In a two-electrode system, the operation temperature (25/50/80 °C) can greatly influence the electrochemical performance of the carbon-1000 sample, especially with an extended voltage window (∼ 3 V). The temperature-dependent operation makes it possible for the application of supercapacitors under extreme conditions.

The electrode is the key part of the electrochemical capacitors, so the electrode material is the most important ingredient in determining their properties. In this study, a simple carbonization method has been presented to prepare porous carbons as electrode materials without activation process, in which inexpensive, reproducible calcium lignosulfonate serves as carbon source. The carbon products were characterized by means of thermogravimetric analysis, X-ray diffraction, field emission scanning electron microscopy and BET surface area measurement. It clearly reveals that the carbonization temperature involved has the crucial effect upon the porous structures as well as the resultant capacitive performances. Given the results from cyclic voltammetry and galvanostatic charge–discharge measurements in 6 M KOH aqueous solution, the present carbons possess high specific capacitance and excellent cycle stability. The maximum specific capacitance reaches as much as 182 F g−1 at the current density of 1 mA cm−2, corresponding to a BET surface area of 1362 m2 g−1, and ca. 95% of the capacitance remains even after 1000 charge–discharge cycles. The present carbons are excellent electrodes candidates for high-rate electrochemical capacitors.

In this work, we demonstrate a simple and effective carbonization method to prepare porous carbon without any activation process, using calcium citrate as carbon source. The carbon products were well characterized by means of thermogravimetric analysis, X-ray diffraction pattern, field emission scanning electron microscopy and BET surface area measurement. It is found out that the carbonization temperature plays a crucial effect on the structures and electrochemical properties of the carbons. Because of the coexistence of major amount of mesopores and minor micropores towards the carbon at 700 °C, the sequences of capacitance values are: 700 °C > 800 °C > 600 °C. As a result, the maximum specific capacitance of the carbon at 700 °C reaches as much as 172 F g−1 at the current density of 1 mA cm−2, which corresponds to a BET surface area of 1072 m2 g−1, also confirming the nonlinear relationship between the specific surface area and the capacitance. Meanwhile, the maximum energy density and power density of the carbon at 700 °C are 24 Wh kg−1 and 6.7 kW kg−1, respectively. Owing to the high specific capacitance and good cycle stability, the present carbons are excellent electrode materials for high-rate electrochemical capacitors.Graphical abstractHighlights► A simple carbonization method has been developed to prepare porous carbon. ► The carbonization temperature has a crucial effect on the capacitive properties. ► The carbons possess high BET surface areas and narrow PSD. ► The carbons possess high specific capacitance and excellent cycle stability.

In this work, NiCo2O4 coral-like porous crystals, nanoparticles and submicron-sized particles have been systematically prepared via a facile sol–gel method, using citric acid as the chelating ligand and H2O (H2O-DMF) as solvent. The experimental results reveal that the initial molar concentration of reactants, reaction time and solvent species involved are crucial for preparing the target products. The as-obtained samples were characterized by means of XRPD, FESEM, HRTEM, EDS and SAED techniques. Finally, the electrochemical performances of NiCo2O4 crystals with distinct morphologies were evaluated by cyclic voltammetry, and galvanostatic charge–discharge cycling techniques. The results show that submicron-sized NiCo2O4 particles exhibit the best capacitive properties with high specific capacitance and excellent cycle stability. At a high mass loading (5.6 mg cm−2), specific capacitance value of submicron-sized NiCo2O4/Ni electrode reaches as much as 217 F g−1, and 96.3% of which can be still maintained after 600 charge–discharge cycles. Therefore, NiCo2O4 crystal is very promising for real application in supercapacitors.

In this work, a series of carbonate minerals including CaCO3, BaCO3 and SrCO3 have been prepared in H2O–ethylene glycol (EG) solution at room temperature, which further serve as hosts to prepare the phosphors doped with Eu3+. The as-obtained samples were characterized by means of XRPD, FESEM, and PL techniques. The experimental results reveal that the volume composition of mixed solvents and additives were crucial for producing samples with discriminating size, shape and phase. In addition, the luminescent properties of CaCO3:Eu3+, BaCO3:Eu3+, and SrCO3:Eu3+ phosphors were briefly studied by excitation spectra, and emission spectra. Remarkably, many scientific merits involved in this study might appear as follows: (1) simply changing the solvent composition or adding additives in mixed solution can realize the crystal growth of carbonates with controlled size, shape and phase; and (2) the as-prepared phosphors doped with Eu3+ could be directly crystallized from an aqueous solution at room temperature without subsequent calcinations.

In this work, a series of porous Eu2+-doped alkaline earth aluminates phosphors including MAl2O4:Eu2+ (Eu3+), Dy3+ (M = Sr, Ca, Ba) have been prepared by Pechini-type sol–gel approach, using citric acid as chelating ligand and ethylene glycol (or H2O) as solvent. The as-obtained samples were characterized by means of XRPD, FESEM and PL techniques. MAl2O4:Eu2+, Dy3+ (M = Sr, Ca, Ba) phosphors were prepared in a reducing atmosphere (H2/Ar, 20 + 80%) while MAl2O4:Eu3+, Dy3+ (M = Sr, Ca, Ba) phosphors were obtained in air. Upon changing the molar ratio of citric acid to total metal cations concentration in ethylene glycol can produce spherical phosphors and the higher molar ratio favors the formation of spherical ones. Otherwise, irregular shaped phosphors occur when conducting the reaction in pure H2O. The irregular shaped phosphors have higher emission intensity than those spherical ones observed with the help of excitation spectra, emission spectra and decay curves.Highlights► Porous aluminate phosphors were prepared by Pechini-type sol–gel approach. ► Spherical and irregular shaped phosphors can be respectively prepared in ethylene glycol and pure H2O. ► The irregular shaped phosphors have higher emission intensity than those spherical ones.

ZnAl2O4:Eu3+ hollow nanophosphors have been for the first time prepared by using carbon nanospheres as hard templates. The ZnAl2O4:Eu3+ hollow nanophosphors were well characterized by means of XRPD, FESEM, TEM, HRTEM, N2 adsorption and desorption and PL techniques. The N2 adsorption and desorption data reveal the porous nature of ZnAl2O4:Eu3+ hollow nanophosphors and high surface area of 195.3 m2 g−1. The PL measurement illustrates red-emitting feature of ZnAl2O4:Eu3+ hollow nanophosphors arising from the characteristic transitions of Eu3+ from 5D0 → 7Fj (j = 0, 1, 2, 3, and 4). This simple and efficient synthetic strategy could be extended to prepare other series of aluminates nanophosphors with novel hollow structures.ZnAl2O4:Eu3+ hollow nanophosphors have been for the first time prepared by using carbon nanospheres as hard templates.

We demonstrated here the hydrothermal synthetic method to prepare 1-D NH4Al(OH)2CO3 nanowires acting as the sacrificial template, which were further converted into 1-D nanoporous ZnAl2O4:Eu3+ phosphors under calcining conditions. The as-prepared ZnAl2O4:Eu3+ phosphors were well characterized by means of XRPD, FESEM, TEM, HRTEM, N2 adsorption and desorption, and PL techniques. The experimental results reveal that the sacrificial template of NH4Al(OH)2CO3 nanowires plays the crucial role in the formation of 1-D nanoporous ZnAl2O4:Eu3+ phosphors. The N2 adsorption and desorption data show the mesoporous property of ZnAl2O4:Eu3+ phosphors, having the surface area of 39.75 m2 g−1. The photoluminescent excitation and emission spectra illustrate the excellent red-emitting property of ZnAl2O4:Eu3+ phosphors. In particular, this synthetic strategy can be extended to prepare other kinds of 1-D nanoporous aluminates such as CoAl2O4 and CuAl2O4, clearly indicating its generality and significance.

We demonstrate herein a facile hydrothermal synthesis followed by post-annealing approach to selectively prepare MgAl2O4:Eu3+ nanoplates and nanoparticles. Series of scientific techniques such as XRPD, FESEM, TEM, HRTEM, and PL were adopted to characterize the as-prepared MgAl2O4:Eu3+ phosphors. First, by altering the amount of hexamethylenetetramine (abbr. HMTA) in solution, MgAl2O4:Eu3+ nanoplates occurred. Next, MgAl2O4:Eu3+ nanoparticles were prepared by adding certain amounts of sodium citrate and sodium dodecylbenzenesulfonate (abbr. SDBS). In particular, the MgAl2O4:Eu3+ nanoplates have novel porous structures. Besides, the MgAl2O4:Eu3+ phosphors exhibit excellent red-emitting properties based upon the characteristic transitions of Eu3+ from 5D0 → 7FJ (J = 0, 1, 2, 3, and 4).

Spherical porous Eu3+-doped ZnAl2O4 phosphors have been prepared by post-annealing the sample at 800 °C for 3 h, which was firstly obtained via a simple PEG-assisted hydrothermal route. The as-prepared ZnAl2O4:Eu3+ phosphors were well characterized by means of XRPD, FESEM, TEM, HRTEM, N2 adsorption and desorption and PL techniques. The experimental results reveal that the amount of PEG 2000 in solution plays the crucial role in the formation of spherical porous ZnAl2O4:Eu3+ phosphors. The N2 adsorption and desorption data reveal the mesoporous property of ZnAl2O4:Eu3+ phosphors, having the high surface area of 40.02 m2 g−1. The photoluminescent excitation and emission spectra illustrate the red-emitting property of ZnAl2O4:Eu3+ phosphors owing to the characteristic transitions of Eu3+ from 5D0 → 7Fj (j = 0, 1, 2, 3, and 4).

In this work, Sr3Al2O6: Eu2+ (Eu3+), Dy3+ phosphors have been prepared by hydrothermal treatment and subsequently postannealing approach, using Sr(NO3)2, Al(NO3)3·9H2O, and CO(NH2)2 as starting materials. The as-obtained phosphors were characterized by means of XRPD, FESEM, and PL techniques. In addition, many reaction parameters were studied in detail, including the initial mole ratios, hydrothermal reaction temperature, calcination temperature and calcination atmosphere. Remarkably, two scientific merits exist herein: Sr3Al2O6: Eu2+ (Eu3+), Dy3+ phosphors can be selectively obtained in a reducing atmosphere (H2/Ar, 20%+80%) and in air, respectively; adding certain amount of sodium citrate can alter the shape and size of Sr3Al2O6: Eu2+ (Eu3+), Dy3+ phosphors in essence. Besides, the luminescent properties of Sr3Al2O6: Eu2+ (Eu3+), Dy3+ phosphors were studied by excitation spectra, emission spectra and decay curves.We present a simple and efficient hydrothermal treatment and subsequently postannealing approach to prepare Sr3Al2O6: Eu2+ (Eu3+), Dy3+ phosphors on a large scale.

We demonstrated here the solvothermal synthetic method to selectively prepare magnetic greigite (Fe3S4) nanosheets and nanoparticles in the mixed solvents of ethylene glycol (EG) and H2O. The as-prepared Fe3S4 nanomaterials were further converted into hematite (α-Fe2O3) having branched structures under calcining conditions. The samples were well characterized by means of XRPD, FESEM, TEM, HRTEM, TGA and magnetic hysteresis curves. The experimental results reveal that the reaction parameters including the composition of mixed solvents, solvothermal temperature, and calcination temperature play important roles on achieving pure phase Fe3S4 and α-Fe2O3 samples. Significantly, we for the first time studied the elevated-temperature oxidation behavior of Fe3S4 sample into α-Fe2O3 in air, accompanying with the size and shape changing dramatically. The magnetic hysteresis curves of Fe3S4 show the ferromagnetic behaviors at room temperature.

The MgAl2O4:Eu3+ phosphors with various morphologies including spherical and rod-like porous structure have been synthesized via a simple and efficient hydrothermal process followed by a post-annealing approach. The experimental results demonstrated that the amounts of urea and PEG 2000 play important roles in the controllable formation of spherical or rod-like phosphors. The N2 adsorption and desorption data showed MgAl2O4:Eu3+ phosphors with the high surface areas of 34.55 and 50.42 m2 g−1. The photoluminescent excitation and emission spectra indicated the excellent red-emitting property of MgAl2O4:Eu3+ phosphors due to the characteristic transitions of Eu3+ from 5D0 → 7Fj (j = 0, 1, 2, 3, and 4).

We have developed a novel biomolecule-assisted hydrothermal method to prepare Sb2S3 and Bi2S3 nanocrystals with various sizes and shapes, in which cysteine combined with other sulfur source can exert the synergistic effect on products. The samples were characterized XRPD, TEM, HRTEM, FESEM, and PL techniques. First, we prepared a series of Sb2S3 and Bi2S3 nanocrystals by simply adjusting the composition of sulfur sources under hydrothermal conditions. Then, we studied the elevated-temperature oxidation behavior of these sulfides in air, which can lead to the formation of α-Sb2O4 and Bi2O3 samples at 600 °C for 3 h. The optical properties of the α-Sb2O4 and Bi2O3 samples were also discussed.

We demonstrate a facile but efficient hydrothermal method for the preparation of ultrafine gahnite (ZnAl2O4) nanoparticles without post-treatment by varying the reaction parameters, including reaction temperature, reaction time and basic source. These parameters were systematically investigated in terms of XRD and TEM techniques. The experimental results revealed that the reaction temperature and basic source play the crucial roles in obtaining ZnAl2O4 sample, whereas the reaction time has minor influence. Significantly, we successfully prepared ZnAl2O4 sample at 180 °C, using urea as the basic source, which is the lowest reaction temperature ever reported for the preparation of ZnAl2O4. In addition, the ZnAl2O4 samples prepared under various conditions exhibit strong emission at room temperature.

We present a simple template carbonization method to produce nanoporous carbons in which potassium biphthalate and magnesium powder serve as the carbon source and hard template, respectively. It reveals that increasing the carbonization temperature can lead to an increase in crystallinity but porosity and the resultant electrochemical performance in supercapacitor application also decreases. The carbon-3:1-800 sample that was obtained by carbonizing potassium biphthalate and magnesium powder (mass ratio of 3:1) at 800 °C exhibits the best electrochemical performance. It has the largest BET surface area of 1745.6 m2 g−1 and a high pore volume of 1.46 cm3 g−1. When measured in a three-electrode system, the carbon-3:1-800 sample delivers a large specific capacitance of 234.2 F g−1 at a current density of 1 A g−1 and high capacitance retention of 96.6% even after 10000 cycles. More importantly, the influence of the operation temperature of the carbon-3:1-800 sample on the electrochemical behavior was also investigated in a two-electrode system. The energy density can reach up to 96.9 W h kg−1 in the case of the power density of 1.5 kW kg−1; it also reveals that a higher operation temperature can result in better electrochemical performance, enabling its implementation under extreme circumstances.

In present work, we demonstrate a simple but effective strategy for high-performance supercapacitors by adding the p-nitroaniline (PNA) into an alkaline electrolyte of KOH. PNA possesses a unique molecular structure with the functional groups of –NH2 and –NO2. Besides, both the product of nitro-reduction (–NH2) and intrinsic –NH2 on the benzene ring can lead to the occurrence of Faradaic redox reactions accompanied by the electron/proton transfer in the mixed electrolytes, whose pseudocapacitance can greatly enhance the total capacitance. Furthermore, another effective additive of the dimethylglyoxime (DMG) has been incorporated into carbon materials for further improving the performances of supercapacitors with a PNA + KOH electrolyte. As for the DMG + PNA + KOH system, a galvanostatic capacitance up to 386.1 F g−1 of the DMG-0.15–PNA-0.15 sample at 3 A g−1, which is nearly two times higher than that of the PNA-0.15 sample (183.6 F g−1) in the PNA + KOH system and nearly three-fold capacitance of the carbon-blank (132.3 F g−1) in the KOH system at the same current density. Furthermore, the specific capacitance still can reach up to 260.0 F g−1 even at 40 A g−1 with a 67.4% capacitance retention ratio. Besides, the DMG-0.15–PNA-0.15 sample exhibits an exceptional capacitance retention of 113% after 5000 charge/discharge cycles by virtue of the potential activated process, which clearly reveals the excellent cycling stability. These remarkable enhancements are ascribed to the synergistic effects of novel additives of PNA and DMG.

High performance nitrogen-doped porous carbon for supercapacitors, named as Gelatin–Mg–Zn-1:5:3, has been successfully prepared via a dual-template carbonization method, without any physical/chemical activation process, in which gelatin serves as both carbon/nitrogen source, and low cost Mg(NO3)2·6H2O and Zn(NO3)2·6H2O as dual templates. It is revealed that the carbonization temperature, and the mass ratio of gelatin–Mg(NO3)2·6H2O–Zn(NO3)2·6H2O plays a crucial role in the determination of surface area, pore structure and the correlative capacitive behavior of the Gelatin–Mg–Zn-1:5:3 sample. It displays a high BET surface area of 1518 m2 g−1, large total pore volume of 4.27 cm3 g−1, and large average pore width of 11.3 nm. In a three electrode system, using 6 mol L−1 KOH solution as electrolyte, we can achieve a high specific capacitance of ca. 284.1 F g−1 at a current density of 1 A g−1 and high capacitance retention of ca. 31.2% is obtained at 150 A g−1, indicating high rate capability. It also possesses a high capacitance retention of ca. 96.1% even after charging/discharging for 10000 cycles. More importantly, a two electrode system, using [EMIm]BF4/AN (weight ratio of 1:1) as electrolyte, has been adopted for the Gelatin–Mg–Zn-1:5:3 sample with different operation temperatures of 25/50/80 °C. As a result, wide voltage windows, broad operation temperatures, and high cycling stability achieved in the two electrode system make it possible for practical application under extreme conditions.

A hard–soft dual templates method has been developed for the first time to prepare porous carbons by the direct carbonization of phenol formaldehyde resins (PFs), Zn(NO3)2·6H2O and polyvinyl butyral (PVB) at 1000 °C under Ar gas, in which PFs serve as the carbon source. More importantly, Zn(NO3)2·6H2O and PVB acting as hard and soft template, respectively, can be readily removed through the evaporation process, resulting in pure carbon without any post-treatment, commonly employed. The PF-Zn-PVB-1:5:1 sample has a total BET surface area of 864 m2 g−1, and a total pore volume of 0.76 cm3 g−1. An electrode based on the porous carbons exhibits the high specific capacitances of 174.7 F g−1 and 152.8 F g−1 at the current densities of 0.5 and 1.0 A g−1, respectively. It also exhibits a superior rate capability, with high specific capacitance retention at ca. 63.1% at a high current density of 20 A g−1. Significantly, about 96.2% is retained after charging and discharging for 10000 cycles, revealing its long-term electrochemical stability. The hard–soft dual templates method proposed in the present work is straightforward and effective, and can be utilized to synthesize porous carbons on a large scale for the application of high performance supercapacitors.

Producing nanoporous carbons that possess high porosity and superior electrochemical performance is a challenge for scientists. In this work, a simple and efficient template carbonization method, without any physical/chemical activation treatment, has been implemented to produce nanoporous carbons doped with nitrogen species. 4-(4-Nitrophenylazo)resorcinol serves as a carbon/nitrogen source and Mg(OH)2 as a hard template. All resultant carbon samples are amorphous, highly porous in nature and display sheet-like nanostructures. The carbon-1:3-L sample whose precursor is obtained by solution method exhibits better porosity, and larger nitrogen content, than those obtained by solid state method (the carbon-1:3-S sample). The carbon-1:3-L sample exhibits large specific surface area (SBET) of 1427.7 m2 g−1, and high total pore volume (VT) of 5.91 cm3 g−1, whereas those of the carbon-1:3-S sample are of 1036.6 m2 g−1 and 4.76 cm3 g−1, respectively. Notably, the present pore volumes are much higher than most of the previously reported for nanoporous carbons. As a consequence, the carbon-1:3-L sample delivers superior electrochemical behaviors, whose specific capacitance reaches up to 378.5 F g−1 when measured at 1 A g−1 in a three-electrode system, compared with that of 263.4 F g−1 of the carbon-1:3-S sample. The present Mg(OH)2-assisted template carbonization method is simple and easy to operate, indicating its potential application for producing nanoporous carbons.

As a generalized synthetic protocol, porous carbons have been for the first time prepared by a direct carbonization of polyacrylate–metal complexes. The case of magnesium polyacrylate was emphatically studied. It reveals that the carbonization temperature can play a crucial role in the determination of surface areas, pore structures, surface functionalities of porous carbons as well as the correlative capacitive performances. The carbon-Mg-900 sample exhibits a high surface area of 942 m2 g−1 and a large total pore volume of 1.90 cm3 g−1, with a high specific capacitance of 262.4 F g−1 at 0.5 A g−1 in 6.0 mol L−1 aqueous KOH electrolyte. Moreover, it displays high capacitance retention even of 33.5% at 100 A g−1, and long-term cycling ability (∼91.3% retention after 5000 cycles). More importantly, the present synthetic strategy can be extended to prepare other polyacrylate–metal complexes, such as calcium polyacrylate and aluminum polyacrylate. The carbon-Al-900 sample can exhibit a high surface area of 1556 m2 g−1 and a large total pore volume of 0.97 cm3 g−1. To sum up, the carbon samples derived from magnesium polyacrylate possess the highest capacitive performances as supercapacitor electrode materials.

In this work, a series of porous carbon materials with hierarchical porosities have been synthesized via a template carbonization method, in which cheap CaCO3 serves as a template and glucose as a carbon precursor. During the carbonization process, CO2 produced by the decomposition of the CaCO3 template can act as an internal activating agent, significantly improving microporosity and mesoporosity. All the carbon materials obtained by regulating the ratio of glucose to CaCO3 exhibit the amorphous features with a low graphitization degree. Among them, the carbon-1:2 sample shows a high BET surface area of up to 818.5 m2 g−1 and a large total pore volume of 1.78 cm3 g−1 as well as a specific capacitance of 107.0 F g−1 at 1 A g−1. In addition, a series of hydroquinone (HQ), p-aminophenol (PAP) and p-nitrophenol (PNP) as novel redox additives that can produce pseudo-capacitances have been added into the KOH electrolyte for promoting the total capacitive performances via redox reactions at the electrode–electrolyte interface. As expected, a 2.5-fold increase in the galvanostatic capacitance of 240.0 F g−1 in the HQ-0.5 electrolyte occurs, compared with the conventional KOH electrolyte. Similarly, the PAP-0.5 electrolyte and the PNP-0.5 electrolyte also show a high specific capacitance of 184.0 F g−1 at 2 A g−1 (156.6 F g−1 at 3 A g−1) and 153.0 F g−1 at 3 A g−1, respectively. Additionally, the three kinds of electrolytes exhibit excellent cyclic stability. The remarkable improvement of supercapacitors is attributed to the quick reversible Faradaic reactions of amine and hydroxyl groups adhering to the phenyl rings, which largely accelerates electron migration and brings additional pseudocapacitive contribution for carbon-based supercapacitors.

In this work, we demonstrate a novel and general synthetic approach for producing nanoporous carbon materials, using adipic acid and zinc powder as raw materials. The mass ratio and carbonization temperature have crucial effects on the structure and electrochemical behavior of the carbon samples. The optimum sample is carbon-1:2-700; it is amorphous in nature and has a high BET surface area of 1426 m2 g−1 and a very large pore volume of 5.92 cm3 g−1. What's more, the sample takes on sheet-like structures entirely composed of nanopores. The electrochemical performance is measured in a three-electrode system using 6 mol L−1 KOH as the electrolyte, and a two-electrode system using [EMIm]BF4/AN as the electrolyte, respectively. In the three-electrode system, it delivers a high specific capacitance of 373.3 F g−1 at a current density of 2 A g−1. Furthermore, it displays a good cycling durability of 93.9% after 10000 cycles. In the two-electrode system, the voltage window has been largely broadened and a series of temperature-dependent measurements are adopted. More importantly, the present synthetic method can be extended to other chemical substances as carbon precursors to produce porous carbon, which can greatly enrich the field of porous carbon synthesis as well as their application as supercapacitors.