Synchrotron Radiation in Situ X-ray Absorption Fine Structure and in Situ X-ray Diffraction Analysis of a High-Performance Cobalt Catalyst Towards the Oxygen Reduction Reaction

Transition metal-based composites are one of the most important electrocatalysts because of their rich redox chemistry. The reaction kinetics of a redox couple is dependent on the chemical valence and is a key issue in electrocatalytic performance. In this study, a metallic Co catalyst was synthesized by pyrolyzing Co(OH)(2). The effect of the chemical valence of Co on the oxygen reduction reaction ( ORR) was investigated by comparing the electrocatalytic properties of three Co-based catalysts containing Co-0, Co2+, and Co3+. The electrocatalytic properties were evaluated mainly by linear scan voltammetry (LSV) and a direct borohydride fuel cell (DBFC) where the Co-based catalysts were used as cathodes. The LSV results show that the ORR peak current density increases with a decrease in chemical valence. The DBFC with the Co-0 cathode exhibits highest power density and good durability. In situ X-ray diffraction combined with in situ X-ray absorption fine structure tests was carried out to reveal the dynamic microstructure evolution of the Co-0 cathode during ORR. The in situ results clearly demonstrate the evolution of metallic Co to Co(OH) (2) and then to CoOOH during the ORR.