Transformation of a Cobalt Carbide (Co₃C) Oxygen Evolution Precatalyst

We report on the fabrication of cobalt carbide (Co3C) particles via a wet-chemical synthetic procedure and also describe their electrochemical oxidation to amorphous Co oxide particles that can be used as oxygen evolution reaction (OER) catalysts. Metal chalcogenide, carbide, and pnictide materials have been investigated recently, but there is some controversy regarding the composition of the actual electrocatalytic material. Carbides, in particular, have not been heavily studied as OER catalysts, and their catalytic nature is still an open question. In an effort to contribute to the clarification of the catalytic particle composition during OER, we have thoroughly characterized the elemental composition of the cobalt carbide particles at various times during OER testing and found that the particles are first converted to a transitory core–shell structure (Co3C core–amorphous Co oxide shell) followed by the gradual but complete conversion to an amorphous Co oxide particle during additional electrochemical OER testing. This amorphous Co oxide particle (derived from Co3C) maintains the shape of the original parent Co3C particle and exhibits a high electrochemically active surface area (ECSA). Moreover, the amorphous Co oxide particle derived from Co3C shows a higher geometric OER activity than either commercial Co oxide particles or Co3C–CoOx core–shell particles. We also observe that the fully oxidized Co3C shows the same intrinsic activity as commercial Co oxide particles when normalized by the ECSA. Accordingly, the amorphous Co oxide particles produced from Co3C possesses a porous nanostructure capable of electrocatalytically oxidizing water within the internal pores of the particles.