Selective phosphidation and reduction strategy to construct heterostructured porous nanorod of CoP coated on Mn₃O₄ as a bifunctional electrocatalyst for overall water splitting

Decent activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the same electrolyte have great practical significance in the development of clean and sustainable alternative energy. Herein, for the first time, heterostructured porous nanorod of CoP nanoparticles anchored on Mn3O4 porous nanorods (Mn₃O₄/CoP PNRs) was fabricated via a selective phosphidation and targeted reduction strategy from MnO2/Co₃O₄ precursor. Due to the in-situ conversion process, an interpenetrated interface Mn-O-Co-P are formed, which may induce a strong electronic coupling effect between CoP and Mn₃O₄, thus improving the charge transfer and electrocatalytic activity. Well, phosphorization can also modulate the surface structure of spinel Mn_x²⁺Mn_3-x³⁺O₄, which may enhance its electrical conductivity and inspire its activity. The heterostructured Mn₃O₄/CoP PNRs exhibits superior HER and OER activity, as evidenced by low overpotentials of 43 mV (vs. HER) and 306 mV (vs. OER), to achieve a current density of 10 mA cm⁻², small Tafel slopes of 28.9 mV dec⁻¹ (vs. HER) and 51.8 mV dec⁻¹ (vs. OER) in an alkaline medium. Impressively, an alkaline overall water-splitting electrolyzer made of this catalyst only requires a low cell voltage of 1.599 V to reach 10 mA cm⁻², which is comparable to the most cobalt phosphide-based catalysts.