Self-Activation of a Polyoxometalate-Derived Composite Electrocatalyst for the Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction (OER) is a key step to access "green hydrogen" by splitting water into O-2 and H-2. Here, we present a molecule-in-material integration concept based on immobilizing the polyoxometalate (POM) anion ([Co-4(H2O)(2)(PW9O34)(2)](10-)) as a molecular precursor on commercial TiO2 (P25) nanoparticles using the cationic polymer polyethylenimine (PEI) as a linking agent. The resulting composite shows promising electrocatalytic OER performance in 0.1 M aqueous KOH solution over prolonged periods (>10 h), during which a remarkable self-activation is observed, leading to a decreased OER overpotential, increased current density, and high Faradaic efficiency (91 +/- 1%). Mechanistic studies shed light on the underlying reasons for this self-activation and show that the formation of a highly active cobalt oxide and/or hydroxide catalyst and an increase in the electrocatalytically active surface area as well as electrical conductivity are the main contributing factors. The reported approach enables the scalable fabrication of POM-derived composite electrocatalysts, while self-activation could be a viable route to the more robust and more active electrocatalysts for challenging energy-conversion reactions.