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

A manganese containing polyoxometalate (POM) [Mn-3(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 [Mn-3(H2O)(5)(PW9O34)(2)](9-) (2) and [Mn-3(H2O)(3)(AsW9O33)(2)](12-) (3) show no to slight photocatalytic O-2 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 (THpANO(3)) 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. (C) 2017 Elsevier B.V. All rights reserved.