Polyaniline/graphene (PANI/graphene) composites are the most investigated electrode materials for supercapacitors, owing to their high specific capacitance and excellent rate performance. However, a specific capacitance larger than the theoretical limit of the composite has been frequently reported for PANI/graphene composites, and the reason for this over-high capacitance has not been understood. In this work, after systematically investigating the evolution of the electrochemical and spectral properties of PANI/graphene, we prove that the hydroxyl- or amino-terminated oligoanilines generated from degradation of PANI possess a large specific capacitance (>1000 F g−1), and they significantly increase the total specific capacitance of the composite electrode. Graphene in the composite serves as a conductive matrix for electron transport between the low-conductivity hydroxyl or amino-terminated oligoanilines and the current collector. Based on the above results, we put forward a suggestion for simultaneously improving the specific capacitance and cycling stability of the PANI/graphene composites. A PANI/reduced graphene oxide composite material with a specific capacitance of 719 F g−1 at 1.4 A g−1 and 91.3% capacitance retention after 10 000 cycles is obtained.

Graphene foams (GFs) have attracted increasing attention because they combine the unique properties of cellular materials and the excellent performance of graphene. The preparation of GFs depends mainly on the self-assembly of graphene or graphene oxide sheets, and designing and controlling the cell morphology of GFs, which determines their properties, remain a challenge. Here, we report a novel strategy for preparing GFs with a hierarchical porous structure. Our preparation method involves mechanically foaming a graphene oxide dispersion with the assistance of a surfactant, followed by lyophilization and thermal reduction. These novel GFs possess large cells created using the bubbles as templates and small pores around the edges of the cells resulting from the self-assembly of the graphene oxide sheets. Because of their unique cell structure, the GFs exhibit an ultra-low density, high porosity, good electrical conductivity, and excellent elasticity. In particular, these GFs exhibit a very large absorption capacity (600–1500 g g−1) for oils and organic solvents. Our work explores a new strategy for controlling the cell morphology and improving the performance of GFs; the results may shed new light on the relationship between the structure and properties of 3D graphene assemblies.

Electroactive polymers constitute an important class of electrode materials for supercapacitors based on pseudocapacitance. However, it is difficult to utilize low-conductive electroactive polymers in supercapacitors, although these polymers may have large theoretical specific capacitance. In this article, we designed and prepared a novel type of electrode material, with a unique structure of low-conductive electroactive polyhydroquinone (PHQ) coated on a highly conductive three-dimensional (3D) porous graphene hydrogel (GHG). PHQ–GHG composites were prepared via a one-step reaction between graphene oxide and hydroquinone under mild conditions. Because PHQ has a large theoretical specific capacitance, and GHG possesses a 3D porous structure, large specific surface area and high electrical conductivity, the composites showed a high specific capacitance of 490 F g−1 at a current density of 24 A g−1, as well as excellent rate performance and cycling stability. These results demonstrate that PHQ–GHG composites are promising electrode materials for supercapacitors, and the method developed in this paper paves a new way for utilizing those electroactive polymers of low electrical conductivities in supercapacitors.

The self-discharge (SDC) process of active electrolyte enhanced supercapacitors (AEESCs) was investigated systematically. The AEESC with hydroquinone as an active electrolyte showed higher specific capacitance but much faster SDC compared with electronic double layer supercapacitors. The electrode process of the above AEESC was studied, and the mechanism of the SDC process was investigated quantitatively. The migration of the active electrolyte between two electrodes of the device was found to be the primary reason for the fast SDC. Two strategies were designed to suppress the migration of the active electrolyte. Following these strategies, two new AEESCs were fabricated, with a Nafion® membrane as the separator and CuSO4 as the active electrolyte. The two AEESCs showed both high specific capacitances and longer SDC times, demonstrating that the problem of poor energy retention of AEESCs was successfully solved.

An electrochemical supercapacitor with a polymeric active electrolyte was designed and fabricated in this work. A water-soluble conducting polymer, sulfonated polyaniline (SPAni), was used in the supercapacitor as the active electrolyte and a semipermeable membrane was employed as the separator of the device. It was found that SPAni in the electrolyte can provide pseudocapacitance via its reversible electrochemical redox reaction. Owing to the good stability of SPAni, the supercapacitor has a long cycling life. Moreover, the migration of SPAni between the two electrodes was blocked by the semipermeable membrane separator, thus self-discharge caused by the shuttle effect of SPAni was suppressed. The research in this paper demonstrates the possibility of using a polymer as the active electrolyte in a supercapacitor and has paved a new way to achieve active electrolyte enhanced supercapacitors with high capacitance and good energy retention.

Suitable electrode interfacial layers are essential to the high performance of perovskite planar heterojunction solar cells. In this letter, we report magnetron sputtered zinc oxide (ZnO) film as the cathode interlayer for methylammonium lead iodide (CH3NH3PbI3) perovskite solar cell. Scanning electron microscopy and X-ray diffraction analysis demonstrate that the sputtered ZnO films consist of c-axis aligned nanorods. The solar cells based on this ZnO cathode interlayer showed high short circuit current and power conversion efficiency. Besides, the performance of the device is insensitive to the thickness of ZnO cathode interlayer. Considering the high reliability and maturity of sputtering technique both in lab and industry, we believe that the sputtered ZnO films are promising cathode interlayers for perovskite solar cells, especially in large-scale production.Keywords: electron transport layer; flexible solar cell; short circuit current

In this paper, a green and facile method based on substrate-enhanced electroless deposition is designed for the fabrication of three-dimensional (3D) metal nanoparticle@graphene hydrogel (MNP@GHG) composites. A galvanic cell was constructed by inducing nickel foam as the substrate of GHG, to enhance the deposition of MNPs via galvanic cell reaction. Various MNPs with redox potential higher than that of Ni, including Au, Pt, Pd and Cu, were successfully deposited onto GHG. The produced gold nanoparticles/GHG composite showed good electrocatalytic activity and was used to fabricate an amperometric sensor towards uric acid with good sensitivity.

Water pollution is one of the most pervasive problems afflicting people throughout the world, while adsorption is the most widely used method to remove the contaminants from water. Here, in this paper, we report an eco-friendly graphene oxide–chitosan (GO–CS) hydrogel as a new type of adsorbent for water purification. The GO–CS hydrogels were prepared via self-assembly of GO sheets and CS chains. A three-dimensional network composed of GO sheets crosslinked by CS was found in GO–CS hydrogels. The GO–CS composite hydrogels showed high adsorption capacity towards different contaminants, including cationic and anionic dyes, as well as heavy metal ions. The mechanism of the dye adsorption was investigated with a spectral method, and an electrostatic interaction was found to be the major interaction between ionic dyes and the hydrogel. The influence of the hydrogel composition on the adsorption capacity towards different adsorbates was also studied. Finally, it was demonstrated that the GO–CS hydrogel can be used as column packing, to fabricate a column for water purification by filtration.

Porous composites based on basic aluminum sulfate and graphene hydrogel (BAS@GHG) were prepared via homogeneous precipitation of BAS in GHG, and used as adsorbents for fluoride removal from water. The BAS@GHG composites have a porous structure with a chemically converted graphene three dimensional network coated by a thin layer of amorphous BAS. These composites showed high adsorption capacities of up to 33.4 mg g−1 at equilibrium fluoride concentrations of 10.7 mg L−1 and temperatures of 298 K, higher than those of previously reported graphene and aluminum-based adsorbents. The adsorption kinetics and isotherm were analyzed by fitting experimental data with pseudo-first-order kinetics, the Weber–Morris model and Langmuir equations. The effects of temperature, pH value, and co-existing anions on the adsorption of fluoride were also investigated.

Chemically converted graphene–room temperature ionic liquid (CCG–RTIL) porous materials were prepared by electrochemical reducing graphene oxide followed by solvent exchange. The resulted CCG–RTIL materials possess 3D porous structure with textured surface, and show good stability in air. Under laser irradiation the temperature of CCG–RTIL materials increased rapidly and significantly, indicating the high photothermal conversion ability of these materials. The influence of CCG–RTIL thickness on the photothermal conversion performance was investigated. These CCG–RTIL materials were used as light absorbers to modify thermoelectric devices, forming light-driven thermoelectric generators, and significantly enhanced the performance of these devices. This work suggests that CCG–RTIL porous materials prepared by this electrochemical method are promising light absorbers for solar electric generation and other photo-thermo-electric conversion devices.

A general method for the fabrication of three-dimensional (3D) porous graphene-based composite materials is reported. This method involves two consecutive electrochemical steps. Firstly, 3D graphene (ERGO) porous material is prepared electrochemically by reducing a concentrated graphene oxide dispersion. Subsequently, the second component is electrochemically deposited onto this 3D ERGO matrix, yielding graphene-based 3D porous composite material. The prepared graphene-based composite materials have a conductive graphene network as the matrix, onto which the second component is homogeneously coated. Conducting polymers, noble metal nanoparticles and metal oxide were successfully incorporated into ERGO architectures, demonstrating the versatility of this method. Taking the ERGO–polyaniline composite as an example, the influence of deposition rate on the morphology of the composite was investigated. Finally, the application of the composite materials prepared with our method was discussed. The high surface area and low electrolyte transport resistance make these electrosynthesized composites suitable electrode materials for electrochemical devices. The ERGO–polyaniline composite electrode showed a high specific capacitance of 716 F g−1 at 0.47 A g−1, and this capacitance could be maintained at 502 F g−1 as the discharge current density was increased up to 4.2 A g−1.

Water pollution is one of the most pervasive problems afflicting people throughout the world, while adsorption is the most widely used method to remove the contaminants from water. Here, in this paper, we report an eco-friendly graphene oxide–chitosan (GO–CS) hydrogel as a new type of adsorbent for water purification. The GO–CS hydrogels were prepared via self-assembly of GO sheets and CS chains. A three-dimensional network composed of GO sheets crosslinked by CS was found in GO–CS hydrogels. The GO–CS composite hydrogels showed high adsorption capacity towards different contaminants, including cationic and anionic dyes, as well as heavy metal ions. The mechanism of the dye adsorption was investigated with a spectral method, and an electrostatic interaction was found to be the major interaction between ionic dyes and the hydrogel. The influence of the hydrogel composition on the adsorption capacity towards different adsorbates was also studied. Finally, it was demonstrated that the GO–CS hydrogel can be used as column packing, to fabricate a column for water purification by filtration.

An electrochemical supercapacitor with a polymeric active electrolyte was designed and fabricated in this work. A water-soluble conducting polymer, sulfonated polyaniline (SPAni), was used in the supercapacitor as the active electrolyte and a semipermeable membrane was employed as the separator of the device. It was found that SPAni in the electrolyte can provide pseudocapacitance via its reversible electrochemical redox reaction. Owing to the good stability of SPAni, the supercapacitor has a long cycling life. Moreover, the migration of SPAni between the two electrodes was blocked by the semipermeable membrane separator, thus self-discharge caused by the shuttle effect of SPAni was suppressed. The research in this paper demonstrates the possibility of using a polymer as the active electrolyte in a supercapacitor and has paved a new way to achieve active electrolyte enhanced supercapacitors with high capacitance and good energy retention.

A general method for the fabrication of three-dimensional (3D) porous graphene-based composite materials is reported. This method involves two consecutive electrochemical steps. Firstly, 3D graphene (ERGO) porous material is prepared electrochemically by reducing a concentrated graphene oxide dispersion. Subsequently, the second component is electrochemically deposited onto this 3D ERGO matrix, yielding graphene-based 3D porous composite material. The prepared graphene-based composite materials have a conductive graphene network as the matrix, onto which the second component is homogeneously coated. Conducting polymers, noble metal nanoparticles and metal oxide were successfully incorporated into ERGO architectures, demonstrating the versatility of this method. Taking the ERGO–polyaniline composite as an example, the influence of deposition rate on the morphology of the composite was investigated. Finally, the application of the composite materials prepared with our method was discussed. The high surface area and low electrolyte transport resistance make these electrosynthesized composites suitable electrode materials for electrochemical devices. The ERGO–polyaniline composite electrode showed a high specific capacitance of 716 F g−1 at 0.47 A g−1, and this capacitance could be maintained at 502 F g−1 as the discharge current density was increased up to 4.2 A g−1.

Porous composites based on basic aluminum sulfate and graphene hydrogel (BAS@GHG) were prepared via homogeneous precipitation of BAS in GHG, and used as adsorbents for fluoride removal from water. The BAS@GHG composites have a porous structure with a chemically converted graphene three dimensional network coated by a thin layer of amorphous BAS. These composites showed high adsorption capacities of up to 33.4 mg g−1 at equilibrium fluoride concentrations of 10.7 mg L−1 and temperatures of 298 K, higher than those of previously reported graphene and aluminum-based adsorbents. The adsorption kinetics and isotherm were analyzed by fitting experimental data with pseudo-first-order kinetics, the Weber–Morris model and Langmuir equations. The effects of temperature, pH value, and co-existing anions on the adsorption of fluoride were also investigated.

Chemically converted graphene–room temperature ionic liquid (CCG–RTIL) porous materials were prepared by electrochemical reducing graphene oxide followed by solvent exchange. The resulted CCG–RTIL materials possess 3D porous structure with textured surface, and show good stability in air. Under laser irradiation the temperature of CCG–RTIL materials increased rapidly and significantly, indicating the high photothermal conversion ability of these materials. The influence of CCG–RTIL thickness on the photothermal conversion performance was investigated. These CCG–RTIL materials were used as light absorbers to modify thermoelectric devices, forming light-driven thermoelectric generators, and significantly enhanced the performance of these devices. This work suggests that CCG–RTIL porous materials prepared by this electrochemical method are promising light absorbers for solar electric generation and other photo-thermo-electric conversion devices.

Graphene foams (GFs) have attracted increasing attention because they combine the unique properties of cellular materials and the excellent performance of graphene. The preparation of GFs depends mainly on the self-assembly of graphene or graphene oxide sheets, and designing and controlling the cell morphology of GFs, which determines their properties, remain a challenge. Here, we report a novel strategy for preparing GFs with a hierarchical porous structure. Our preparation method involves mechanically foaming a graphene oxide dispersion with the assistance of a surfactant, followed by lyophilization and thermal reduction. These novel GFs possess large cells created using the bubbles as templates and small pores around the edges of the cells resulting from the self-assembly of the graphene oxide sheets. Because of their unique cell structure, the GFs exhibit an ultra-low density, high porosity, good electrical conductivity, and excellent elasticity. In particular, these GFs exhibit a very large absorption capacity (600–1500 g g−1) for oils and organic solvents. Our work explores a new strategy for controlling the cell morphology and improving the performance of GFs; the results may shed new light on the relationship between the structure and properties of 3D graphene assemblies.

Electroactive polymers constitute an important class of electrode materials for supercapacitors based on pseudocapacitance. However, it is difficult to utilize low-conductive electroactive polymers in supercapacitors, although these polymers may have large theoretical specific capacitance. In this article, we designed and prepared a novel type of electrode material, with a unique structure of low-conductive electroactive polyhydroquinone (PHQ) coated on a highly conductive three-dimensional (3D) porous graphene hydrogel (GHG). PHQ–GHG composites were prepared via a one-step reaction between graphene oxide and hydroquinone under mild conditions. Because PHQ has a large theoretical specific capacitance, and GHG possesses a 3D porous structure, large specific surface area and high electrical conductivity, the composites showed a high specific capacitance of 490 F g−1 at a current density of 24 A g−1, as well as excellent rate performance and cycling stability. These results demonstrate that PHQ–GHG composites are promising electrode materials for supercapacitors, and the method developed in this paper paves a new way for utilizing those electroactive polymers of low electrical conductivities in supercapacitors.