Tailoring the electronic structure of Ni5P4/Ni2P catalyst by Co2P for efficient overall water electrolysis

The advancement of highly-active bifunctional electrocatalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for reducing costs and improving efficiency. Phosphides, as the representative of bifunctional catalysts, can be used for HER and OER by virtue of the special metal/phosphorus coordination mode and the ordered surface reconstruction. However, the inappropriate adsorption/desorption energy for intermediates, poor reaction kinetics and scant activation analysis limit their large-scale application. Here, we developed a novel Ni/Co phosphide multi-component heterostructure catalyst on Ni foam (Co2P/NixPy@NF) through hydrothermal treatment and low temperature phosphorization. Benefitting from open hierarchical structures, abundant active sites, rapid mass/charge transfer rates, and modified electronic structures, the optimal catalyst exhibits excellent activity and high stability towards HER (155 mV overpotential in 1.0 M KOH and 175 mV overpotential in 0.5 M H2SO4 at 100 mA·cm−2), OER (300 mV in 1.0 M KOH at 100 mA·cm−2), and overall water electrolysis (1.74 V cell voltage in 1.0 M KOH at 100 mA·cm−2). Post-stability analysis further reveals that hydroxide and oxyhydroxide are generated on catalysts' surfaces during HER and OER, respectively, in alkaline electrolytes. These activation processes result in the catalysts' surfaces forming new heterostructures which reorganize the electronic structure. These morphology optimizations, heterostructure engineering and investigation of activation reported here have been effective strategies for designing and exploring hybrid materials as fabulous catalysts to generate renewable energy.