High‐Voltage‐Enabled Stable Cobalt Species Deposition on MnO2 for Water Oxidation in Acid

The design and maintenance of highly active sites in an acidic environment is vital and challenging for the oxygen evolution reaction (OER). In this work, it is found that the obtained CoO2 under high applied potential can be stable on MnO2 host in acidic environment, which may act as an effective means to solve the instability of cobalt-based electrocatalyst. The significant improvement of acidic OER activity (6.9 times) and stability (46.4 times) of 90-Co-MnO2 (treated by molten salt with more Co deposition sites) demonstrates the advantages of this approach. In situ Raman and the Pourbaix diagram suggest that the enhanced performance derives from the stable presence of CoO2 at the voltage >1.8 V versus reversible hydrogen electrode (RHE). However, when the potential is <1.8 V, the corresponding other cobalt species is too unstable to facilitate the OER. Density functional theorycalculations reveal that the deposited cobalt oxides can act as active sites, thus effectively reducing the reaction energy barrier of the rate-determining step. This work provides a new perspective for enhancing the stability of cobalt-based electrocatalyst. In the future, the dual consideration of applied potential and stable species of active element in the Pourbaix diagram may be a new direction for developing acid-stable electrocatalysts.