Oxygen evolution reaction efficiently catalyzed by a quasi-single-crystalline cobalt fluoride

Abstract

Surface engineering for the active phase of metal (oxy)hydroxide species formation in the oxygen-evolution reaction (OER) catalysts is significant for water splitting reaction in hydrogen fuel generation. Herein, we demonstrate the OER efficiently catalyzed by a novel quasi-single-crystalline cobalt fluoride, and reveal its surface structure evolution during the OER process that is instructive for catalysis process understanding and novel catalysts design. Because of strong ionic bonding dissociation driven by the chemical and electrochemical conditions, the structural evolution can readily generate such an active phase during the OER process. The X-ray photoelectron spectroscopy, in-situ Raman spectrum and microscopic observation confirm the structure evolution from pure cobalt fluoride to cobalt oxy/hydroxide over their surface, and the chemical anionic reconstruction induced cobalt oxy/hydroxide passive layer formation. The 3D nanoflower nanostructure can efficiently expose more active sites and increase mass transportation by expanding the contact surface to the electrolyte. Remarkably, no activation is required to reach stable catalytic performance. It only needs an overpotential as low as 285 mV to afford 10 mA cm−2 with a small Tafel slope of 60 mV dec-1, outperforming the state-of-the-art IrO2 catalyst and some analogs transitional metal-based catalyst. It also shows excellent stability. The current findings are instructive in understanding OER catalytic reaction and active Co-based catalysts fabrication.