POLYOXOMETALATES AS ACTIVE WATER OXIDATION CATALYSTS IN NEUTRAL CONDITIONS

2017 edition

Marta Blasco Ahicart

Finding a solution to the increasing energy demand worldwide is, arguably, the biggest challenge that scientists are facing in the present decade[1]. A straightforward approach to face this problem is the development of an artificial photosynthesis device, where water is splitted into its main elements, H2and O2, using renewable energy. These products can be transformed afterwards, by fuel cell technology, into water and energy. One of the bottlenecks in this field is the lack of a cheap, robust and efficient catalyst for the oxygen evolution reaction (OER). In this work we study the activity towards OER in neutral conditions of three polyoxometalate species based on earth-abundant metals when incorporated into carbon/hydrocarbon electrodes: {Co9(H2O)6(OH)3(HPO4)2(PW9O34)3}16- (Co9)[2], {Co4(H2O)2(PW9O34)2}10 (Co4 Keggin)[3] and {Co4(H2O)2(P2W15O56)2}10 (Co4 Wells-Dawson).

Polyoxometalates (POMs) are an extensively studied class of discrete polyoxoanionic molecules built from fragments of high-valent metal oxides. They have been proposed as potential candidates for water oxidation catalysis[4], although its stability in homogeneous conditions has been put into doubt. That is the reason why a suitable strategy to obtain insoluble cesium salts of these compounds has been developed. These new species are active towards OER in heterogeneous conditions and its genuine activity during the catalytic process is determined by several characterization analyses after electrocatalytic experiments.

[1] Lewis, N. S.; Nocera, D. G.; Powering the planet: Chemical challenges in solar energy utilization. Proceedings of the National Academy of Sciences of the United States of America 2006, 103 (43), 15729-15735.

[2] Goberna-Ferrón, S.; Vigara, L.; Soriano-López, J.; Galán-Mascarós, J. R.; Identification of a Nonanuclear {CoII9} Polyoxometalate Cluster as a Homogeneous Catalyst for Water Oxidation. Inorganic Chemistry 2012, 51 (21), 11707-11715.

[3] Yin, Q.; Miles Tan, J.; Besson, C.; Geletii, Y. V.; Musaev, D. G.; Kuznetsov, A. E.; Luo, Z.; Hardcastle K. I.; Hill, C. L.; A fast soluble carbon-free molecular water oxidation catalyst based on abundant metals. Science 2010, 328, 342-345.

[4] Soriano-López, J.; Goberna-Ferrón, S.; Vigara, L.; Carbó, J. J.; Poblet, J. M.; Galán-Mascarós, J. R.; Cobalt Polyoxometalates as Heterogeneous Water Oxidation Catalysts. Inorganic Chemistry 2013, 52 (9), 4753-4755.