Design and synthesis of Ni-Co-X(X = O, S, P)/Co(OH)2 core/shell layered nanosheets as multifunctional electrodes for hydrogen electrocatalysts and supercapacitors

The requirements of the morphology and material properties in common make it possible to integrate the two functional electrodes, hydrogen electrocatalyst and supercapacitor, into one material system. The order of electrochemical performance of core materials was ranked as NiCoP > NiCo2S4 > NiCo2O4. By constructing core/shell heterostructure, Ni-Co-X/Co(OH)2 composites achieved the boost of electrochemical performance than individual Ni-Co-X. Particularly, the NiCoP/Co(OH)2 composite synthesized under optimal conditions presented both excellent catalytic activity and charge storage capability. The NiCoP/Co(OH)2 composite needed small overpotential of 73 mV to drive current density of 10 mA cm−2 in 1 M KOH, displayed Tafel slope of 75 mV dec−1 and long-term stability over 15 h without obvious fluctuation. Moreover, the NiCoP/Co(OH)2 composite showed high specific capacitance of 1604 F g−1 at 1 A g−1, delivered remarkable rate capability of 81.8 % at 20 A g−1 and cyclic stability with 91.8 % capacity retention over 5000 cycles. The impressive electrochemical properties of NiCoP/Co(OH)2 composite is attributed to the enriched active sites, enhanced electronic conductivity and strong synergistic effect. Our research provides insights and effective strategies for the design and synthesis of integrated electrodes for hydrogen electrocatalysts and supercapacitors.