Operando Spectroscopic Analysis of CoP Films Electrocatalyzing the Hydrogen-Evolution Reaction

Transition metal phosphides exhibit high catalytic activity towards the electrochemical hydrogen-evolution reaction (HER) and resist chemical corrosion in acidic solutions. For example, an electrodeposited CoP catalyst exhibited an overpotential, η, of -η < 100 mV at a current density of -10 mA cm^(-2) in 0.500 M H_2SO_4(aq). To obtain a chemical description of the material as-prepared and also while effecting the HER in acidic media, such electrocatalyst films were investigated using Raman spectroscopy and X-ray absorption spectroscopy both ex-situ as well as under in-situ and operando conditions in 0.500 M H_2SO_4(aq). Ex-situ analysis using the tandem spectroscopies indicated the presence of multiple ordered and disordered phases that contained both near-zero valent and oxidized Co species, in addition to reduced and oxygenated P species. Operando analysis indicated that the active electrocatalyst was primarily amorphous and predominantly consisted of near-zero-valent Co as well as reduced P