Polyoxometalate-based manganese clusters as catalysts for efficient photocatalytic and electrochemical water oxidation

- A series of different manganese-containing POMs were synthesized and characterized by multiple experiments.
- The catalytic water oxidation activities of Mn-containing POMs were investigated in photochemical and electrochemical manner.
- For the first time, we implemented EIS to confirm the differences between POM containing Mn and the equivalent Mn2+ (aq.).
- Multiple experiments confirm that [Mn3(H2O)3(SbW9O33)2]12− is a homogeneous molecular catalyst.

A manganese containing polyoxometalate (POM) [Mn3(H2O)3(SbW9O33)2]12− (1) was synthesized and characterized in detail. The photocatalytic activity of 1 is definitely better than other manganese containing POM water oxidation catalysts reported so far according to oxygen yield, whereas the analogues [Mn3(H2O)5(PW9O34)2]9− (2) and [Mn3(H2O)3(AsW9O33)2]12− (3) show no to slight photocatalytic O2 evolution amount. Meanwhile, the electrocatalytic activities of 1-3 were investigated in 80 mM pH 9.0 borate buffer, which follows the catalytic activity order of 1 > 2 > 3. Multiple experiments including UV−vis absorption, catalysts aging experiments, tetra-n-heptylammonium nitrate (THpANO3) toluene extraction, electrochemical experiments and capillary electrophoretic measurements results confirm that catalyst 1 is a homogeneous molecular catalyst. No Mn2+ (aq.) or manganese oxide under the reaction conditions of photocatalytic and electrochemical water oxidation was detected.

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