Architecture of Biomimetic Water Oxidation Catalyst with Mn₄CaO₅ Clusterlike Structure Unit

Mn₄CaO₅ cluster in green plant is considered as the ideal structure for water oxidation catalysis. However, this structure is difficult to be constructed in heterogeneous catalyst because of its distorted spatial structure and unique electronic state. Herein, we report the synthesis of two-dimensional biomimetic Ca-Mn-O catalyst with Mn₄CaO₅ clusterlike structure through ultrasonic-assisted reduction treatment toward Ca-birnessite. The synergistic effect between ultrasonic and reduction successfully reduced the Mn oxidation state in Ca-birnessite without breaking the structure of MnO₂ monolayers, forming a regular two-dimensional structure with Mn₄CaO₅ cubanelike structure unit for the first time. The biomimetic catalyst shows a superior water oxidation activity (turnover frequency = 3.43 s^-1), which is the best in manganese-based heterogeneous catalyst to date. This work provides a new strategy for the precise synthesis of specific structure and exhibits a great prospect of biomimic in heterogeneous catalyst.