Solvothermal preparation of nickel-iron phosphides hollow nanospheres derived from metal-organic frameworks for water oxidation reaction

Abstract

Developing active and stable water oxidation electrocatalysts is desired to increase the efficiency of water electrolyzers. Nickel phosphides have been reported as pre-catalysts for water oxidation reaction. However, their catalytic activities can further be improved through morphology engineering and tuning electronic structures. Here, nickel-iron phosphides hollow nanospheres ((Ni1-xFex)2P, x = 0–0.35) were synthesized through solvothermal treatment of Ni-Fe metal-organic framework precursors with white phosphorus. The hollow nanospheres have diameters around 20–50 nm, with the crystalized structure resembles Ni2P phase. When used to catalyze the water oxidation reaction in 1 M KOH, the (Ni0.73Fe0.27)2P/Ni foam electrode exhibits best catalytic performance, with only 243 mV overpotentials to reach 10 mA cm−2 (loading 0.135 mgNi+Fe cm−2), and with a Tafel slope ~ 30 mV dec−1. The enhanced water oxidation activity is mainly owing to the electronic interaction between Ni and Fe. Ex-situ characterizations of the (Ni0.73Fe0.27)2P after water oxidation reaction reveal that surface phosphides are transformed into layered double hydroxides under anodic alkaline conditions. The solvothermal prepared (Ni1-xFex)2P hollow nanospheres can be a potential candidate as pre-catalysts for water oxidation reaction in water electrolyzers.