Designed formation of hierarchical core-shell NiCo2S4 @NiMoO4 arrays on cornstalk biochar as battery-type electrodes for hybrid supercapacitors

Cornstalk biochar (CB) has a highly hollow and porous structure, which can provide large specific surface area, shorten the ion transport path, facilitate rapid charge transmission and enhance the material conductivity. In this paper, core-shell NiCo2S4 @NiMoO4 arrays supported on the surface of cornstalk biochar (NMONCS@CB) were prepared. The combination of NiCo2S4 @NiMoO4 and cornstalk biochar removes the poor conductivity limitations of NiCo2S4 @NiMoO4. At the same time, synergistic effects significantly widen the operating potential window of the composite and enhance the energy density. The electrode material has excellent electrochemical properties (1447 F·g−1 at the current densities of 5 mA·cm−2) and good stability (specific capacitance reduction limited to 12% after 10,000 cycles). A NMONCS@CB//CB supercapacitor was fabricated using NMONCS@CB as cathode, CB as anode and nickel foam as current collector. This device has a high energy density (78.23 Wh·kg−1 at 184.49 W·kg−1) and good stability (the specific capacitance decreased by only 20% after 10,000 cycles). Two identical devices connected in parallel can power a red LED (1.8 V) for 30 min.