3D Architectures of Quaternary Co-Ni-S-P/Graphene Hybrids as Highly Active and Stable Bifunctional Electrocatalysts for Overall Water Splitting

Developing low-cost, highly active, and stable bifunctional electrocatalysts is a challenging issue in electrochemical water electrolysis. Building on 3D architectured electrocatalysts through structural and compositional engineering is an effective strategy to enhance catalytic activities as well as stability and durability. Herein, 3D architectures of quaternary Co-Ni-S-P compounds coupled with graphene ((Co_{1− x}Ni_x)(S_{1− y}P_y)₂/G) electrocatalysts are proposed, in which nanosheets are self-assembled to form 3D architectures with round and flat doughnut-like shapes, toward overall water splitting. Benefiting from the 3D architectures and Ni, P substitution, (Co_{1− x}Ni_x)(S_{1− y}P_y)₂/G exhibits superior electrocatalytic activities with low overpotentials of 117 and 285 mV at 10 mA cm⁻² and Tafel slopes of 85 and 105 mV dec⁻¹ for hydrogen and oxygen evolution reactions, respectively, in alkaline media. In addition, minimal increases in overpotential are observed, even after the 10 000th voltammetric cycle and continuous chronopotentiometric testing over 50–100 h, confirming the high stability and durability of (Co_{1− x}Ni_x)(S_{1− y}P_y)₂/G. When used as both cathode and anode, (Co_{1− x}Ni_x)(S_{1− y}P_y)₂/G achieves excellent overall water splitting performance with a cell potential as low as 1.65 V, reaching a current density of 10 mA cm⁻² with no obvious decay after 50 h, demonstrating that (Co_{1− x}Ni_x)(S_{1− y}P_y)₂/G is an efficient bifunctional electrocatalyst for overall water splitting.