Manipulating the d-band centers of transition metal phosphides through dual metal doping towards robust overall water splitting

Abstract

Integrating bifunctional electrocatalysts into one electrolytic cell for water electrolysis has exhibited great convenience and high efficiency in green hydrogen production. However, the opportune adsorptions of intermediate oxygen and hydrogen species on catalytic active sites are prerequisites for the design of high-performing bifunctional electrocatalysts to simultaneously drive oxygen and hydrogen evolution reactions (OER/HER). In this work, we developed a dual metal doping strategy to manipulate the d-band centers of non-precious transition metal phosphides aiming at optimal intermediate adsorption towards robust overall water splitting. The Ni and Mn atom incorporated FeP nanoarrays (Ni–Mn–FeP) were grown directly on NiFe foam via sequential etching-depositing and phosphorization processes. As for the well-known sluggish OER process, Ni–Mn–FeP only requires an overpotential of 185 mV to deliver 10 mA cm⁻² in alkaline media. Meanwhile, the HER can also be driven at a low overpotential of 103 mV. In particular, when bifunctional Ni–Mn–FeP as both the cathode and anode is assembled into an electrolytic cell, the electrolysis current of 100 mA cm⁻² can be easily achieved at a low cell voltage of 1.55 V and the stability at 500 mA cm⁻² can last for 360 h, implying great prospects for large-scale applications. The d-band center theory indicated that the intrinsic high electroactivity of bifunctional Ni–Mn–FeP should arise from the doping induced notable promotions in *O to *OOH conversion and H* adsorption processes. The collaboration approach of codoped low-valence and high-valence metals may inspire the development of high-performance and versatile catalysts.