A Co-containing polyoxogermanotungstate for alkaline electrocatalytic water oxidation†

Efficient electrocatalysts for the oxygen evolution reaction (OER) are paramount to the development of electrochemical devices for clean energy and fuel conversion. However, due to the complicated structures of heterogeneous electrocatalysts, it is a great challenge to elucidate the intrinsic activity of the catalytic sites on their surfaces. In this work, we report the synthesis and characterisation of a 9-Co(II)-containing trimetric cyclic polyoxogermanotungstate cluster, K₉Na₃H₇[Co₉(H₂O)₆(OH)₃(SeO₃)₂(B-α-GeW₉O₃₄)₃]·39H₂O (Co₉-POT), which exhibits distinct physicochemical properties and a well-defined single-crystal structure. The triangular nonacobalt(II)-oxo cluster {Co₉(H₂O)₆(OH)₃(SeO₃)₂} ({Co₉Se₂}) in Co₉-POT consists of three identical quasi-cubane {Co₃O₄} subunits capped by two SeO₃²⁻ anions. Co₉-POT exhibits electrocatalytic activity for the alkaline OER, with a turnover frequency (TOF) of the catalytically active site Co of 0.18 s⁻¹ at an overpotential of 400 mV. In situ operational Raman and electrochemical impedance spectroscopy techniques explicitly capture the dynamic evolution of the OER process. This work provides insights into the structure–performance relationship in the OER process and the design of electrocatalysts with high atomic activity.