In-situ electrochemical self-tuning of amorphous nickel molybdenum phosphate to crystal Ni-rich compound for enhanced overall water splitting

Developing bifunctional electrocatalyst with low-cost, high-activity, and durability towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is the key for large-scale hydrogen production . In this paper, a novel one-dimensional amorphous nickel molybdenum phosphate nanoarray (NiMoPO x ) is prepared on nickel foam via two-step reations. NiMoPO x exhibits excellent electrocatalytic activity than the state of the art Pt/C and RuO 2 . For overall water splitting reaction, NiMoPO x electrode couple achieves 1.55 V at 10 mA cm −2 for prolonged 50 h operation in 1.0 M KOH. The excellent bifunctional electrocatalytic properties come from the in-situ electrochemical surface self-tuning of NiMoPO x “precatalyst”. During the self-tuning process, the surface of amorphous NiMoPO x is in-situ transformed to metallic Ni and Ni(OH) 2 nanoparticles under HER and OER, leading to the formation of special heterostructure hybrid materials . Further investigations indicate that the in-situ produced metallic Ni nanoparticles favor the generatation of adsorbed H atom in water dissociation, therefore enhance the hydrogen evolution kinetics and activity. Meanwhile the in-situ formed Ni(OH) 2 nanoparticles become the actual surficial species to promote oxygen evolution reaction. This self-tuning method provides a new idea to develop high-performance electrocatalysts for some sustainable energy conversion systems, such as water splitting and metal-air batteries .