Understanding the Role of Gold Nanoparticles in Enhancing the Catalytic Activity of Manganese Oxides in Water Oxidation Reactions

The Earth‐abundant and inexpensive manganese oxides (MnO x ) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnO x catalysts are still much lower than that of nanostructured IrO 2 and RuO 2 catalysts. Herein, we demonstrate that doping MnO x polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnO x /AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn 3+ species, a small amount of AuNPs (<5 %) in α‐MnO 2 /AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α‐MnO 2 .