Optimized bimetallic nickel-iron phosphides with rich defects as enhanced electrocatalysts for oxygen evolution reaction

Exploring low-cost and outstanding bimetallic phosphides to substitute noble metals as electrocatalysts for oxygen evolution reaction (OER) in alkaline media is essential for renewable energy technologies. Herein, bimetallic nickel-iron phosphides nanoparticles (P-NiFe-800 NPs) with rich defects have been synthesized through gas annealing at 800 °C and phosphorization using uniform nickel-iron nanocubes (NiFe NCs) as precursor. At optimized calcination temperature, the obtained P-NiFe-800 NPs are composed of uniform nanoparticles with the rough surface, which suggests the larger surface area and more exposed rich active sites than other samples for OER. The introduction of P element to binary nickel-iron metals can optimize the crystalline and electronic structures of NiFe NCs and thus enhance electrocatalytic properties. Owing to the distinct morphological structure and synergistic effect between nickel-iron and phosphorus, P-NiFe-800 NPs demonstrate superior electrocatalytic activities for OER with lower overpotential of 270.1 mV to achieve a current density of 10 mA cm^-2, smaller Tafel slope of 39 mV dec^-1, lower electrochemical impedance spectroscopy (EIS) value, bigger determined double-layer capacitance (C_dl) of 2130 uF cm^-2 and prominent stability than NiFe NCs, NiFe-600 NPs, NiFe-700 NPs, NiFe-800 NPs, NiFe-900 NPs, P-NiFe NCs, P-NiFe-600 NPs, P-NiFe-700 NPs and P-NiFe-900 NPs. The optimized phosphorization is helpful for fabricating the bimetallic phosphides as efficient catalysts for OER.