Electrocatalytic Water Oxidation by a Highly Active and Robust α‐Mn 2 O 3 Thin Film Sintered on a Fluorine‐Doped Tin Oxide Electrode

As a water oxidation catalyst, α‐Mn 2 O 3 has higher activity than other manganese oxides. However, the robustness of the catalyst supported on conducting electrodes has only been tested for a short time (1 h) and it shows a gradual decrease in activity. Furthermore, the turnover number (TON) and turnover frequency (TOF) have not been reported. Herein, we optimized the preparation of transparent nanocrystalline α‐Mn 2 O 3 on a fluorine‐doped tin oxide (FTO) electrode, and this resulting catalyst shows, in neutral aqueous 0.1  m potassium phosphate buffer solution, a high electrocatalytic water oxidation activity with a TON of 230, a TOF of 5.3×10 −3  s −1 based on the all‐Mn content, and a TOF of 2.1 s −1 based on the amount of surface‐active Mn with a Faradic efficiency of 96.7 % at an overpotential of 470 mV. The robustness of the α‐Mn 2 O 3 /FTO electrocatalyst was tested for a long time (80 h) without a decrease in activity.