A bioinspired soluble manganese cluster as a water oxidation electrocatalyst with low overpotential

The electrocatalytic oxidation of water is a challenging step towards the production of hydrogen as an alternative fuel. In nature, water oxidation is catalysed by a high oxidation state Mn4CaO x cluster. The corresponding industrial development of manganese catalysts for water oxidation is very attractive due to the low cost of this metal. A few manganese complexes have been previously explored as water oxidation catalysts using various chemical oxidants in homogeneous and heterogeneous systems. Efficient electrochemical water oxidation catalysed by a soluble manganese-oxo cluster, however, has not been achieved. Here, we report the synthesis and characterization of [Mn12O12(O2CC6H3(OH)2)16(H2O)4] (Mn12DH), a unique example within this class of compounds in being both highly soluble and stable in water. We demonstrate that Mn12DH, which is readily prepared from cheap and environmentally benign starting materials, is a stable homogeneous water oxidation electrocatalyst operating at pH 6 with an exceptionally low overpotential of only 334 mV. During photosynthesis, nature uses an enzyme with a manganese–calcium core for water oxidation. Here, the authors report the synthesis of a stable, water-soluble manganese cluster that acts as a homogeneous water oxidation electrocatalyst, displaying low overpotential and high Faradaic efficiency.