One-pot synthesis of cobalt pyrophosphate nanoparticles combined with mesoporous carbon for asymmetric supercapacitors

One-pot synthesis of the cobalt pyrophosphate (Co2P2O7) nanoparticles combined with mesoporous carbon was fabricated via a simple lyophilization followed by carbonization as an electrode material for asymmetric supercapacitors. Benefiting from nitrogen-rich polyethyleneimine (PEI) polymer as both C and N source and glutaraldehyde as a crosslinking agent, a three-dimensional hierarchical porous structure with dominant mesopores and a few micropores was obtained. It is important to note that glutaraldehyde acts not only to increase porous structure but also to enhance the graphitization of PEI. The electrochemical properties of the Co2P2O7 electrode were investigated in 6 M KOH and displayed excellent electrochemical properties due to the synergistic effect of Co2P2O7 nanoparticles and nitrogen-doped mesoporous carbon layer. The amount of crosslinking agent exhibited a significant influence on the electrochemical properties of the electrode. When the amount of added glutaraldehyde was 200 μl, shown as Co2P2O7@N–C2, the best electrochemical performance was found. The ultrahigh specific capacitance of Co2P2O7@N–C2 was found at 10 mV/s as 384 F/g in a three-electrode configuration. Then, an asymmetric supercapacitor was successfully fabricated, using the Co2P2O7@N–C2 as cathode and the activated carbon (AC) as the anode, and it displayed maximum specific energy of 5.68 Wh/kg at a specific power of 325 W/kg and a maximum specific power of 6500 W/kg at a specific energy of 2.17 Wh/kg. These remarkable electrochemical performances can be ascribed to the nitrogen-doped carbon layer, better graphitization, and enhanced porous structure with abundant mesopores. This facile one-pot method can provide for integrating other transition metal pyrophosphates with nitrogen-doped carbon layer for high-performance supercapacitor electrodes.