ICS84

Preparation of soluble, manganese-based clusters as electrochemical catalysts for water oxidation

Naama Yamin Gluz Ahmad Najar
Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel

Water oxidation is considered to be a challenging step in the generation of molecular hydrogen as an alternative fuel. In this reaction, molecular oxygen is produced, alongside four protons and four electrons, which can be reduced to form the molecular hydrogen. In nature, water oxidation is catalysed by a high-oxidation-state Mn4CaOx cluster called Oxygen Evolving Complex (OEC). The corresponding industrial development of manganese-based water oxidation catalysts (WOCs) is very attractive because of the relatively low cost of manganese. Few manganese clusters have been studied as WOCs using various chemical oxidants in homogenous and heterogeneous systems. However, effective water oxidation catalysed by a soluble manganese cluster has not yet been achieved.

This research is focused on the development of two soluble manganese complexes, Mn12O12(O2CC6H3(OH)2)16(H2O)4 and Mn12O12(O2CC6H3(NH2)2)16(H2O)4. The complexes were developed through the structural emulation of the naturally-occurring OEC, and were used as electrochemical catalysts for water oxidation.

First, Mn12Acetate was prepared, a catalytic central cluster common to the two complexes. Then, the acetate molecules were then replaced by dihydroxybenzoic acid and diaminobenzoic acid in the first and second complex, respectively, in order to prevent cluster hydrolysis. Both complexes were characterized by MS, FTIR and UV-vis.

The efficiency of the two complexes as WOCs was examined by measuring the amount of molecular oxygen released during the reaction, after applying an electric potential determined through the use of cyclic voltammetry. It has been shown that the first complex (with the dihydroxybenzoic acid) and the second (with the diaminobenzoic acid) yielded Faradaic efficiencies of 0.61% and 3.27%, respectively. We conclude that further examination of the efficiency of the complexes should be made, by applying different electric potentials to activate water oxidation process.









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