Metal-organic-framework template-derived hierarchical porous CoP arrays for energy-saving overall water splitting

Highlights: • MOF-based growth-etching-phosphorization strategy was used to fabricate CoP. • The MOF-derived CoP displays 3D hierarchical porous arrays. • Outstanding HER, OER and UOR performance was achieved. • The CoP catalyst delivers 10 mA cm⁻² at an ultralow voltage of 1.38 V in urea. Developing highly active and low-cost electrocatalysts with superior durability is attractive but challenging for energy-saving electrolytic hydrogen generation via water electrolysis. Herein, a novel metal-organic framework (MOF)-based growth-etching-phosphorization strategy is reported to construct hierarchical porous CoP nanostructure arrays on nickel foam substrate (HP-CoP NA/NF) for overall water splitting (OWP). Interconnected 2D cobalt-based MOF are fabricated via an aqueous solution reaction at room temperature, and then solid MOFs are uniformly converted into porous CoP arrays with hierarchical 3D configuration through a Co²⁺−etching process with subsequent phosphorization treatment. This unique array architecture is beneficial for providing highly exposed active sites, shortening ion diffusion path and promoting gas release during the electrochemical reactions. Resultantly, this MOFs-derived CoP catalyst exhibits an outstanding electrocatalytic activity in catalyzing not only hydrogen and oxygen evolution reactions with the low overpotentials of 70 and 258 mV at 10 mA cm⁻², respectively, but also some other small molecules electro-oxidation reactions, especially for urea oxidation reaction. Furthermore, the two-electrode electrolyzer comprising bifunctional HP-CoP NA/NF electrode delivers a current density of 10 mA cm⁻² at an ultralow cell voltage of 1.38 V in the presence of urea, which is 180 mV smaller than that of pure water splitting. This work introduces a reference for the development of MOF-derived hierarchical nanostructured catalysts for energy-saving water splitting.