Doping is an efficient method to promote the electronic conductivity and improve the capacitive performance of electrodes for further energy conversion. Herein, by doping heteroelement metal ions, an ultrathin Y (yttrium)-doped α-Ni(OH)2 nanosheet electrode with a large surface area and hierarchical porous structure is fabricated via a facile approach. The Y-doped α-Ni(OH)2 nanosheets exhibit a high specific capacitance of 1860 F g−1 at a current density of 1 A g−1 mainly due to the increased electronic conductivity of the increased Ni3+ species, as evidenced by density functional theory calculations. As a result, the asymmetric supercapacitor device based on the Y-doped α-Ni(OH)2 nanosheet electrode demonstrates both a remarkably high energy density (58.4 W h kg−1) and power density (754.56 W kg−1).

•A proposal of novel polarization modeling and performance optimization of MHDCFC.•Effect of anodic compartment height on ohmic polarization is firstly described.•The model predicts the main affecting parameters of cell performance.•The performance of cell with graphite is better than that using activated carbon.An electrochemical model for a molten sodium hydroxide direct carbon fuel cell (MHDCFC) is developed based on electrochemical reaction dynamics, mass transfer, and electrode processes in the cell. Activated carbon and graphite are considered the main fuels, and static and dynamic parameters describing polarizations are taken into account for valuation and optimization of cell performance. Asymmetric reaction compartments are used in the MHDCFC, and the effect of the anodic compartment height on polarization is described first. The cell performance mainly depends on temperature (T), the pressures in the anodic (Pan) and cathodic compartments (Pcat), the anodic compartment height (H1), and the fuel type. Besides, cell performance is affected by ohmic polarization, anode activation polarization, cathode concentration polarization, and cathode activation polarization, in order of precedence. At Pan of 1.8 atm, Pcat of 1.7 atm, H1 of 0.06 m, and T of 773–973 K, the efficiencies (e) of the cells with activated carbon and graphite are higher than 50% at current densities of 0–500 A m−2 and 0–700 A m−2, respectively. The maximum power densities (e > 50%) are achieved for activated carbon and graphite and reach 367.6626 W m−2 and 498.9687 W m−2, respectively.

The preparation of porous materials from renewable energy sources is attracting intensive attention due to in terms of the application/economic advantage, and pore structural design is core in the development of efficient supercapacitors or available porous media. In this work, we focused on the transformation of natural biomass, such as cotton, into more stable porous carbonaceous forms for energy storage in practical applications. Biomorphic cotton fibers are pretreated under the effect of NaOH/urea swelling on cellulose and are subsequently used as a biomass carbon source to mold the porous microtubule structure through a certain degree of calcining. As a merit of its favorable structural features, the hierarchical porous carbon fibers exhibit an enhanced electric double layer capacitance (221.7 F g–1 at 0.3 A g–1) and excellent cycling stability (only 4.6% loss was observed after 6000 cycles at 2 A g–1). A detailed investigation displays that biomass-swelling behavior plays a significant role, not only in improving the surface chemical characteristics of biomorphic cotton fibers but also in facilitating the formation of a hierarchical porous carbon fiber structure. In contrast to traditional methods, nickel foams have been used as the collector for supercapacitor that requiring no additional polymeric binders or carbon black as support or conductive materials. Because of the absence of additive materials, we can further enhance capacitance. This remarkable capacitive performance can be due to sufficient void space within the porous microstructure. By effectively increasing the contact area between the carbon surface and the electrolyte, which can reduce the ion diffusion pathway or buffer the volume change during cycling. This approach opens a novel route to produce the abundantly different morphology of porous biomass-based carbon materials and proposes a green alternative method to meet sustainable development needs.Keywords: binderless; biomass-swelling; carbon fibers; cellulose; hierarchical porous carbon; supercapacitor

In this study, we used a direct ultrasonic modified nickel foam in sulfuric acid, which achieved a simple and rapid binder-free electrode, improving the electronic transmission in the electrolyte. It produced a bed of electroactive nickel hydroxide and sulphide with a unique needle-like microstructure, which grew vertically on the surface of the Ni foam straight into the electrolyte, not only increasing the contact interface area between the active material and the electrolyte but also shortening the diffusion length of the ions. The obtained product possesses outstanding electrochemical performance, having a high specific capacitances of 6 F cm−2 at a current density of 5 mA cm−2, which can still retain 2.2 F cm−2, even at a current density as high as 40 mA cm−2. Furthermore, it has excellent cyclic stability with only 5% loss after 1000 cycles.

Coral-like Ni0.9Co1.92Se4 nanostructured materials have been prepared through a simple and controlled two-step solvothermal method, which present a handsome electrochemical performance. The specific capacitance reaches 1021.1 F g−1 under the current density of 2 mA cm−2 over a 0.5 V electrode potential window with an areal capacitance of 6.43 F cm−2. A superior rate capability of 77% is achieved with discharge rates increasing from 2 to 50 mA cm−2, as well as a good cycling stability of 88.39% after 5000 cycles. Furthermore, a good energy density of 26.29 W h kg−1 is achieved under the power density of 265 W kg−1 when assembled into a Ni0.9Co1.92Se4//AC asymmetric supercapacitor with the operating potential window extended to 1.5 V. The high performance can be attributed to the coral-like architectures with rich redox reactions, high conductivity and transport rate for both electrons and electrolyte ions. Our results suggest that the coral-like Ni0.9Co1.92Se4 nanostructured electrode materials may be a good choice for supercapacitors.

Oxygen storage capacity is influenced by the morphology and crystal-plane(s) of CeO2, which can thus affect the ability of this material to oxidise carbon monoxide. To investigate the effect of different morphologies/crystal-planes of CeO2 on the electrocatalytic performance of DMFCs (Direct Methanol Fuel Cell), three different types of CeO2 nanocrystals with different crystal-planes were synthesised and later assembled into Pt–xCeO2/Graphene composites with graphene and Pt nanoparticles as the electrocatalyst for DMFCs. According to the HRTEM images, the original morphology and crystal-plane structures of CeO2 are essentially maintained in the three types of Pt–xCeO2/Graphene composite catalysts investigated in this work. The catalytic performance of the Pt–xCeO2/Graphene composites for methanol electrocatalytic oxidation was investigated by a series of electrochemical measurements. Compared with the other catalysts, Pt–rCeO2/Graphene demonstrates superior catalytic activity (onset potential: 0.15 V) and the strongest resistance to poisoning by carbonaceous species (If/Ib: 2.11). The results of H2-TPR shows that rCeO2 with the {110} facet has the best surface reducibility among the xCeO2 with different facets being investigated, which provides a rationale for the superior performance of the Pt–rCeO2/Graphene catalyst. This study indicates that metallic oxides with a suitable crystal plane and shape can effectively enhance the electrocatalytic performance of Pt-based catalysts for methanol electrooxidation.

The design and development of nanomaterials has become central to the advancement of pseudocapacitive performance. Many one-dimensional nanostructures (1D NSs), two-dimensional nanostructures (2D NSs), and three-dimensional hierarchical structures (3D HSs) composed of these building blocks have been synthesized as pseudocapacitive materials via different methods. However, due to the unclear assembly mechanism of these NSs, reports of HSs simultaneously assembled from two or more types of NSs are rare. In this article, NiCo2O4 multiple hierarchical structures (MHSs) composed of 1D nanowires and 2D nanosheets are simply grown on Ni foam using an ordered two-step hydrothermal synthesis followed by annealing processing. The low-dimensional nanowire is found to hold priority in the growth order, rather than the high-dimensional nanosheet, thus effectively promoting the integration of these different NSs in the assembly of the NiCo2O4 MHSs. With vast electroactive surface area and favorable mesoporous architecture, the NiCo2O4 MHSs exhibit a high specific capacitance of up to 2623.3 F g–1, scaled to the active mass of the NiCo2O4 sample at a current density of 1 A g–1. A nearly constant rate performance of 68% is achieved at a current density ranging from 1 to 40 A g–1, and the sample retains approximately 94% of its maximum capacitance even after 3000 continuous charge–discharge cycles at a consistently high current density of 10 A g–1.Keywords: binder-free electrode; hierarchical structure; hydrothermal synthesis; nickel foam; spinel nickel cobaltate; supercapacitor

Electrochemical oxidative carbonylation of methanol with CO to dimethyl carbonate from heterogeneous electrocatalyst was studied at normal temperature and pressure. For the purpose of decrease the crystalline size and the agglomerative force of metal-organic framework (MOF), this paper first introduced graphite oxide (GO) into MOF/GO hybrid material with enhanced electrocatalytic performance and the stability of electrocatalyst for the dimethyl carbonate (DMC) synthesis. The introduction of GO is important to build the hybrid materials with synergistic properties. The composite materials and its parent materials were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and the electrochemical property of the samples was measured. The results show that the MOF/GO was active for the electrolytic reaction and could be reused at least five times. A plausible Cu(II)/Cu(I) electrocatalytic cycle mechanism was proposed.

The unique composite of Ni@NiO core/shell structure and active carbon (AC) had been synthesized through a two-step method. The Ni2+ was first reduced to Ni on the surface of AC supporter. Then the NiO shell was obtained after the following oxidized treatment. The transmission electron microscopy (TEM) observed that Ni@NiO particles with thin shell were sporadically dispersed on AC surface without vast reaggregation. And the electrochemical impedance spectroscopy (EIS) showed that Ni@NiOcore-shell/AC composite had higher electrical conductivity. Thus, the outside thin NiO shell would expose more electroactive surface and shorten the ionic diffusion distance. While the Ni core could accelerate the electronic transport due to its low contact resistance. When employed as supercapacitor electrodes, Ni@NiOcore-shell/AC composite exhibited a high specific capacitance of ca. 700 F g−1 at 0.5 A g−1 and remained above 90% of the initial capacity after 1000 cycles at 1 A g−1. The high specific capacitance and long cycle life of the hybrid structure made it alternative for energy storage systems.

•We first demonstrated the application of MOF materials to synthesis of DMC.•A novel heterogeneous catalyst for electro-synthesis of DMC.•The Cu(II)-based MOF has an excellent catalytic activity and stability.The development of heterogeneous catalysts, such as metal-organic frameworks (MOFs), may overcome most of the problems associated with homogeneous catalysts. A Cu-based MOF with mixed ligands was synthesized, and its electrocatalytic activity for the oxidative carbonylation of methanol was studied. This study demonstrates for the first time that a Cu-based MOF can actively electrocatalyze methanol into dimethyl carbonate (DMC). A self-designed electrolytic cell was constructed for electrocatalysis experiments. The as-synthesized Cu-based MOF showed a pair of redox peaks at ca. + 0.3 V. This paper utilizes a new approach for synthesizing DMC in a heterogeneous catalytic system.

•Hair was directly carbonized by environmental and energy-saving methods.•Hair was utilized to prepare nitrogen-doped carbon materials for supercapacitor.•A new approache for preparing nitrogen-rich active carbon from biomass waste of hair-like precursor.•Hair-based carbon having a non-crystalline layered structure and excellent capacitive performance.Hair, a high-nitrogen energetic material, is utilized as a precursor for nitrogen-doped porous carbon. The preparation procedures for obtaining carbon from hair are very simple, namely, reductant or deionized water activation process followed by hair carbonization under argon atmosphere at 800 °C for 2 h. The samples are characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption, and X-ray photoelectron microscopy. The carbon samples are tested as electrode materials in supercapacitors in a three-electrode system. The carbon (soaked in deionized water at 80 °C) presents relatively low specific surface areas (441.34 m2 g−1) and shows higher capacitance (154.5 F g−1) compared with nitrogen-free commercial activated carbons (134.5 F g−1) at 5 A g−1. The capacitance remains at 130.5 F g−1 even when the current load is increased to 15 A g−1. The capacitance loss is only 5% in 6 M KOH after 10,000 charge and discharge cycles at 5 A g−1. It is the unique microstructure after activation processing and electroactive nitrogen functionalities that enable the carbon obtained through a simple, ecological, and economical process to be utilized as a potential electrode material for electrical double-layer capacitors.

Electrochemical carbonylation of methanol to dimethyl carbonate (DMC) at room temperature and atmospheric pressure in a self-fabricated two-compartment electrolytic cell was achieved using CuCl2–2,2′-bipyridyl as catalyst. The reaction mechanism was analyzed, and the influence factors such as supporting electrolyte, anode potential, and concentration of supporting electrolyte and CuCl2–2,2′-bipyridyl were evaluated. The proper conditions for the electrosynthesis of DMC were obtained, in which the content of DMC was 0.1279%, the current efficiency of DMC was 76.4%, and the amount of DMC was 0.3161 mmol. In the distilled anolyte after reaction no other species but CH3OH and DMC were found via gas chromatography.

Copper-ceria hybrid composite electrode prepared by electrochemical co-deposition was examined for their redox process and electrocatalytic activities towards the oxidation of methanol. The structure and morphology of electrodes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. XRD pattern of the copper-ceria hybrid composite electrode exhibited some diffraction peaks of CeO2 and SEM micrograph showed that it was composed of grains and flakes. The energy dispersive spectroscopy (EDS) spectrum of this area also showed the presence of cerium. Cyclic voltammetry, CO stripping and chronoamperometry were performed to characterize electrocatalytic property of the prepared samples. In cyclic voltammetry studies and chronoamperometry, copper-ceria hybrid composite electrode towards oxidation of methanol showed a significantly higher response and long term stability. CO stripping results indicated the facile removal of intermediate poisoning species CO in the presence of CeO2, which was helpful for CO and methanol electro-oxidation.CO stripping voltammograms recorded in 0.1 mol/L NaOH solution at 10 mV/s on Cu/Cu (1) and Cu-CeO2/Cu hybrid composite (2) electrode

The one-step electrochemical deposition of highly dispersed platinum nanoparticles on graphene to fabricate a new Pt/EG/GC modified electrode for formaldehyde determination in aqueous solution. Catalyst surface morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), the composition analysis was carried out on energy-dispersive X-ray spectroscopy (EDS). The electrochemical performances of the electrode were investigated by cyclic voltammetry, and clear amperometric responses were obtained in the scan process. The correlation coefficient was 0.998 of the linear relation between current values and concentrations, the Pt/EG/GC electrode exhibited a low limit of detection (0.04 mM), high sensitivity (0.0162 mA mM−1) and long working life. These characteristics make the Pt/EG/GC electrode appropriate for the formaldehyde determination based on formaldehyde electric catalytic oxidation.

Due to their physicochemical properties, Tm2O3 nanoparticles have been employed in bioanalytical applications. In this report, body-centered shaped Tm2O3 nanoparticles with size of about 10 nm were successfully synthesized by the hydrothermal homogeneous method and used as a novel electrochemical biosensing platform for glucose based on a Tm2O3–Nafion modified electrode. Transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) were used to characterize the Tm2O3 nanoparticles, and cyclic voltammetry (CV) was used to investigate the electrochemical behavior of the modified electrode. The experimental results showed that glucose oxidase (GOD) immobilized on the Nafion–Tm2O3 film achieved direct electron transfer with an apparent heterogeneous electron transfer rate constant (ks) of 3.27 ± 0.43 s−1 and kept its bioactivity. Confirmation of the retained bioactivity can be demonstrated by its bioelectrocatalytic activity to the reduction of dissolved oxygen. The GOD/Tm2O3/Nafion/GC electrode displayed potential application for the fabrication of glucose biosensors with a linear glucose response up to 7 mM. Additionally, the biosensor based on the Tm2O3 nanoparticle-modified electrode exhibited good stability and selectivity. The successful practice of using the Tm2O3 modified electrode for the direct electrochemical analysis of proteins and the bioelectrocatalytic activity of enzymes offers an efficient strategy and a new promising platform for the application of rare earth oxide materials in the field of electrochemical sensors.

•NiSe2 counter elecrode for dye-sensitived solar cell.•First ever prepared NiSe2 counter electrode by a novel one-step hydrothermal electrochemical deposition method.•The power conversion efficiency of NiSe2 CE reached 8.24%.The hydrothermal electrochemical deposition (HED) synthesis NiSe2 as counter electrode(CE) of dye-sensitized solar cells(DSSCs), which shows excellent catalytic activity in reduction of triiodide. Hydrothermal and electro-deposition(ED) have been widely used to synthetize NiSe2, herein, we fistly introduce the HED to produce the NiSe2 material as the CE of DSSCs. In addition, cyclic voltammetry(CV) curves, Tafel plots and electrochemical impedance spectroscopy(EIS) indicated that HED-NiSe2 as CE shows better electrocatalytic activity for reduction of iodine/iodide electrolyte than ED-NiSe2 and Pt. The DSSC fabricated by the HED-NiSe2 CE displays a solar-to-electricity conversion efficiency of 8.24% comparing with 7.68% the convention Pt as reference, and significant higher than that of based on the ED-NiSe2(7.97%). Furthermore, we demonstrate that the HED method is a promising way to design and synthesize advanced CE materials for utilizing solar energy.

•The Ni and Co-based composite is applied for pseudocapacitor electrode.•The metallic NiCo2O4 improves the conductivity of the composite.•The composite has 4.625 F cm−2 areal capacitance and 94.66% capacity retention.Poor electronic and ionic conductivities of electrode limit the development of pseudocapacitor. In this study, the NiCo2O4 nanowires array @ NiCo(OH)2 nanosheets growth on Ni foam as a binary composite electrode is synthesized by hydrothermal and electrodeposition methods to improve the electrochemical performance of pseudocapacitor. In the composite electrode, the NiCo2O4 exhibits metallic properties, which is verified by the first principles calculation, and is responsible for the high conductivity of the composite electrode. Electrochemical measurements demonstrate the NiCo2O4 @ NiCo(OH)2 electrode exhibits a high areal capacitance of 4.625 F cm−2 at 1 mA cm−2 (2890.6 F g−1 at 0.625 A g−1) and an excellent cycling stability (maintaining 94.66% capacity after 5000 cycles at 10 mA cm−2). Therefore, this work further extends the research on high conductive architecture electrode and shed some light on the design of applied materials for the future practical energy storage devices.

Doping is an efficient method to promote the electronic conductivity and improve the capacitive performance of electrodes for further energy conversion. Herein, by doping heteroelement metal ions, an ultrathin Y (yttrium)-doped α-Ni(OH)2 nanosheet electrode with a large surface area and hierarchical porous structure is fabricated via a facile approach. The Y-doped α-Ni(OH)2 nanosheets exhibit a high specific capacitance of 1860 F g−1 at a current density of 1 A g−1 mainly due to the increased electronic conductivity of the increased Ni3+ species, as evidenced by density functional theory calculations. As a result, the asymmetric supercapacitor device based on the Y-doped α-Ni(OH)2 nanosheet electrode demonstrates both a remarkably high energy density (58.4 W h kg−1) and power density (754.56 W kg−1).

The one-step electrochemical deposition of highly dispersed platinum nanoparticles on graphene to fabricate a new Pt/EG/GC modified electrode for formaldehyde determination in aqueous solution. Catalyst surface morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), the composition analysis was carried out on energy-dispersive X-ray spectroscopy (EDS). The electrochemical performances of the electrode were investigated by cyclic voltammetry, and clear amperometric responses were obtained in the scan process. The correlation coefficient was 0.998 of the linear relation between current values and concentrations, the Pt/EG/GC electrode exhibited a low limit of detection (0.04 mM), high sensitivity (0.0162 mA mM−1) and long working life. These characteristics make the Pt/EG/GC electrode appropriate for the formaldehyde determination based on formaldehyde electric catalytic oxidation.