Observing the reconstruction of cobalt oxide model catalyst in electrocatalytic water oxidation

Oxygen evolution reaction (OER) is the rate-determining step in water electrolysis. Surface reconstruction induced by external environments and potentials has been proven to enable inactive OER pre-catalysts to become superior oxides/oxyhydroxides that are comparable to the benchmark IrO2/RuO2 catalysts. However, it is still highly challenging to operando probe the reconstruction and precisely identify the true active sites due to the complex composition and structural diversity of practical catalysts. To address the issue, three cobalt-based OER model catalysts are prepared by different treatments of commercial cobalt foil via ultra-high vacuum approaches. The derived Co3O4-film model catalyst exhibits a substantially improved OER activity compared with the other two counterparts, Co-metal and acid etching cobalt sample. Multiple vacuum-connected technologies, including quasi-in situ XPS and time-of-flight secondary ion mass spectroscopy, are conducted and reveal the quantitative compositions and structures of the three-dimensional (3D) active oxides/oxyhydroxides layer reconstructed near the surface. The results suggest that the hydroxyl species and oxygen vacancies coordinated to reversible Co2+ sites within superficial layer are responsible for the OER activity. This study provides valuable insights for the near-surface investigation of model catalysts in OER reconstruction.