MOF-derived Co(Ni)Ox species loading on two-dimensional cobalt phosphide: A Janus electrocatalyst toward efficient and stable overall water splitting

To achieve the requirement of "green chemistry'' in electrocatalysis, finely-adjusting the electronic structure of the electrocatalytic materials proves effective to highly expose surface active sites. In this study, Co(Ni)Ox species loaded on two-dimensional (2D) CoPx nanosheets are designed and fabricated as the Janus structure, and the optimized Co(Ni)Ox@CoPx-3 annealed at 600 °C with appropriate molar ratio (4:1 of Co(Ni)Ox:CoPx) achieved low overpotentials of 97 mV and 309 mV at 10 mA cm−2 for hydrogen and oxygen evolution reactions with reduced Tafel slopes of 19.12 mV dec−1 and 108.42 mV dec−1 in 1.0 M KOH. The excellent catalytic performances could be attributed to the rational design of the Janus structure between transition-metal-oxides and phosphide with regulated surface status eliminating structural hinderance, thus lowering overpotentials, impedance and Tafel slopes, enhancing active surface area and the sluggish kinetics in electrochemical overall water splitting. Vital heterojunctions of CoP/CoNi and CoP/CoNiO were unveiled by mechanistic investigation via density functional theory (DFT) indicating that the rational intrinsic design of Co(Ni)Ox@CoPx Janus electrocatalyst with tremendous potential could be utilized as low-cost and high-efficient water oxidation electrolyzers, which paves a way for the inherent improvement for transition-metal-based Janus electrocatalysts in overall water splitting.