Negative charging of transition-metal phosphides via strong electronic coupling for destabilization of alkaline water

Abstract

Heterogeneous electrocatalysis typically involves charge transfer between surface active sites and adsorbed species. Therefore, modulating the surface charge state of an electrocatalyst can be used to enhance performance. A series of negatively charged transition-metal (Fe, Co, Ni, Cu,and NiCo) phosphides were fabricated by designing strong electronic coupling with hydr(oxy)oxides formed in situ. Physicochemical characterizations, together with DFT computations, demonstrate that strong electronic coupling renders transition-metal phosphides negatively charged. This facilitates destabilization of alkaline water adsorption and dissociation to result in significantly improved H₂ evolution. Negatively charged Ni₂ P/nickel hydr(oxy)oxide for example exhibits a significantly low overpotential of 138 mV at 100 mA cm⁻² , superior to that without strong electronic coupling and also commercial Pt/C.