Wanyong Zhou

The glucose-assisted synthesis of a graphene nanosheet–NiO composite for high-performance supercapacitors

A green and facile approach was used for the synthesis of a graphene nanosheet NiO composite. Using glucose as the green reduction agent, graphene oxide was reduced to graphene and formed a membrane-like NiO–GNS–GC composite via a hydrothermal method. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the electrochemical performance of the composite was evaluated by cyclic voltammetry and galvanostatic charge–discharge. The obtained NiO–GNS–GC composite exhibits the highest specific supercapacitance of 1495 F g−1 at a current density of 0.5 A g−1 in 6 M KOH, which is much higher than that of pure NiO (478 F g−1) and pure GNS (92 F g−1) along with 90% specific capacitance remaining after 1000 cycles. This could be attributed to the layered sandwich nanostructure and the fact that during the hydrothermal process glucose transformed to a kind of amorphous carbon which, as a spacer, could stabilize the structure of the as-prepared GNS.

Effective microwave-assisted synthesis of graphene nanosheets/NiO composite for high-performance supercapacitors

A facile and fast strategy was used for synthesis of a petal-like graphene nanosheets (GNS)/NiO composite. Using this strategy, graphene oxide was reduced to graphene and formed the GNS/NiO composite via a microwave-assisted method without a complicated procedure and any controlling-agent. The product was characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analysis results have confirmed that petal-like NiO sheets are well dispersed on the surfaces of graphene nanosheets. The as-prepared composite was electrochemically tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy as an electrode material for supercapacitors. The GNS/NiO composite exhibits a specific supercapacitance of 799 F g−1 at a current density of 0.3 A g−1 in 6 M KOH electrolyte and a long cycle life, along with 90% specific capacitance remaining after 1000 cycles. The electrochemical performance of the composite was significantly improved compared to bare graphene and NiO. This could be attributed to their architecture. The results presented here suggest that the GNS/NiO composite could have potential applications in high energy storage systems.

Facile synthesis of Mn3O4-rGO hybrid materials for the high-performance electrocatalytic reduction of oxygen

In this study, a highly active oxygen reduction reaction (ORR) electrocatalyst (MG-15) of Mn3O4 nanoparticles (NPs) supported by reduced graphene oxide (rGO) has been fabricated through one-step microwave-assisted synthetic route. Upon microwave-assisted synthesis, the formation of Mn3O4 NPs and the reduction of GO occurs simultaneously. Transmission electron microscope (TEM) profile reveals that Mn3O4 NPs are uniformly distributed evenly on the winkled rGO sheets. The MG-15 hybrid materials show enhanced electrocatalytic activity compared to rGO, Mn3O4 NPs and the mixture of rGO and Mn3O4 NPs, which indicates that the synergistic effect of Mn3O4 and rGO enhances the overall performance. Additional, the oxygen reduction peak of the MG-15 catalyst in a 0.1M KOH solution is tested at -0.15V, which is more positive than Pt/C (-0.154V). The onset potential of the MG-15 is close to Pt/C. Most importantly, the mechanism analysis shows that it favors the 4e- pathway for ORR. Furthermore, the MG-15 also exhibit excellent durability and methanol.

High-performance supercapacitors based on conductive graphene combined with Ni(OH)2 nanoflakes

A green and facile strategy is reported for the synthesis of a three-dimensional (3D) graphene nanosheets (GNS)/Ni(OH)2 composite for use as a supercapacitor material. During this process, graphene oxide was reduced to graphene and Ni(OH)2 was attached in it to form the GNS/Ni(OH)2 composite via a chemical precipitation route without any complicated procedures. The product was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The analyses indicated that the Ni(OH)2 sheets were well interwoven on the surfaces of the graphene nanosheets. Furthermore, the composite was electrochemically tested by cyclic voltammetry, galvanostatic charge/discharge, specific capacitance, and by assessing its cycle life. The GNS/Ni(OH)2 composite exhibited a high specific supercapacitance of 2053 F g−1 at a current density of 0.3 A g−1 in 6 M KOH electrolyte and a long cycle life, along with 97% specific capacitance remaining after 1000 cycles. The GNS/Ni(OH)2 composite had superb electrochemical performance compared to bare Ni(OH)2, which could be attributed to its architecture. These results suggest that the GNS/Ni(OH)2 composite could have potential application as a supercapacitor material.

An effective bifunctional electrocatalysts: Controlled growth of CoFe alloy nanoparticles supported on N-doped carbon nanotubes

Exploring efficient and inexpensive bi-functional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a critical work for developing the fuel cells and the metal-air batteries. Nitrogen-doped carbon and transition metal (Fe or Co) has been demonstrated as promising catalyst due to the synergetic effect. In this work, the CoFe alloy nanoparticles supported on N-doped carbon nanotubes (CoFe@NCNTs) are synthetized by one-step annealing the precursors, without any templates. The as-prepared materials show both extraordinary electrocatalysis activity for ORR and OER in alkaline solution: a diffusion current density of -5.53 mA cm-2, approximate four-electron selectivity as ORR catalyst, a potential of 0.842 V at 10 mA cm-2. Specifically, the CoFe@NCNTs present a Tafel slope of 60.16 mV dec-1 as OER catalyst and the variance (ΔE) is below 1.017 V in 0.1 M KOH for the OER and ORR.