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Biomass carbon materials, which are environmentally friendly, have received significant attention and rapidly developed in the field of electrochemical devices. In this study, rice husk carbon (RHC) was prepared using calcination and activation methods, and a layer of nickel–cobalt double hydroxide (NiCo-LDH) was grown on the surface of RHC using a hydrothermal method, resulting in the formation of the NiCo-LDH@RHC composite. The open nanoflower structure and the synergistic effect between RHC and NiCo-LDH increased the conductivity and stability of the electrode material, as well as its specific capacitance. The NiCo-LDH@RHC electrode delivered a high specific capacity of 8542.5 mF cm−2 at a current density of 2 mA cm−2 with a good cycling stability of 80.45% across 5000 cycles. Furthermore, a high-performance all-solid-state asymmetric supercapacitor (ASC) was assembled using Fe2O3/CC as the anode material and NiCo-LDH@RHC as the cathode material. It displayed a high energy density of 61.44 μW h cm−2 at a power density of 3.99 mW cm−2 and an excellent cycle retention rate of 86.54% after 10 000 cycles. This research demonstrates that NiCo-LDH@RHC is an environmentally friendly and high performance electrode material with great development potential. [ABSTRACT FROM AUTHOR]

Although cobalt pyrophosphate (Co2P2O7) has shown promise as a potential electrocatalyst for the oxygen evolution reaction (OER), its electrocatalytic activity for the oxygen reduction reaction (ORR) has rarely been explored. In this work, a novel composite catalyst with in situ grown Co2P2O7 on nitrogen-doped graphene nanosheets (Co2P2O7/N-rGO) was fabricated by a facile one-step pyrolysis method. Pyrolysis temperature was found to have a significant effect on the morphology, structure and ORR performance of the composites. The catalyst fabricated at 800 °C (Co2P2O7/N-rGO-800) presented ultrasmall Co2P2O7 nanocrystals (below 5 nm) anchored on N-rGO and the highest pyridinic-N proportion. Benefiting from the full exposure of active sites on the ultrasmall Co2P2O7 nanocrystals, abundant pyridinic-N species and the synergistic effect of Co2P2O7 and N-doped graphene, optimized Co2P2O7/N-rGO-800 not only demonstrates excellent ORR catalytic activity with a positive cathodic peak potential (0.823 V vs. 0.833 V of the commercial Pt/C catalyst), but also shows superior durability and methanol crossover resistance to Pt/C in alkaline solution. In addition, the composite catalyst also exhibits reasonable oxygen evolution reaction (OER) performance and impressive OER stability in KOH solution. These findings suggest that the Co2P2O7/N-rGO catalysts may be promising candidates as oxygen electrocatalysts for future energy conversion applications. [ABSTRACT FROM AUTHOR]