Cactus-like NC/Co_xP electrode enables efficient and stable hydrogen evolution for saline water splitting

Designing efficient and robust catalysts for hydrogen evolution reaction (HER) is imperative for saline water electrolysis technology. A catalyst composed of Co_xP nanowires array with N-doped carbon nanosheets (NC) was fabricated on Ni foam (NF) by an in-situ growth strategy. The material is designated as NC/Co_xP@NF. In the preparation process, Co(OH)₂ nanowires were transformed into a metal organic framework of cobalt (ZIF-67) on NF by the dissolution-coordination of endogenous Co²⁺ and 2-methylimidazole. The resulting cactus-like microstructure gives NC/Co_xP@NF abundant exposed active sites and ion transport channels, which improve the HER catalytic reaction kinetics. Furthermore, the interconnected alternating nanowires and free-standing nanosheets in NC/Co_xP@NF improve its structural stability, and the formation of surface polyanions (phosphate) and a NC nanosheet protective layer improve the anti-corrosive properties of catalysts. Thus, the NC/Co_xP@NF has an excellent performance, requiring overpotentials of 107 and 133 mV for HER to achieve 10 mA cm⁻² in 1.0 mol L⁻¹ KOH and 1.0 mol L⁻¹ KOH + 0.5 mol L⁻¹ NaCl, respectively. This in-situ transformation strategy is a new way of constructing highly-efficient HER catalysts for saline water electrolysis.