Homogenous Water Oxidation Electrocatalysis by Peptoid-Cobalt Complexes

During past years, many efforts have been made to develop renewable and sustainable energy generation methods and eliminate the need for carbon-based energy. Hydrogen based fuels are produced from water splitting, and are considered efficient, reliable and sustainable. The most challenging part of water splitting is the water oxidation reaction, as it transfers 4 electrons. A water-oxidation catalyst (WOC) is needed for this reaction to be rapid and efficient.

Many WOCs based on transition-metals have been reported, but WOCs based on earth-abundant non-precious metals have higher economical potential and applicability. Cobalt catalysts are of high interest, as cobalt is abundant and cheap, and moreover, has easily changeable oxidation states, therefore can be used as catalyst in redox processes.

Our approach for developing a WOC is biomimetic, employing N-substituted glycine oligomers, which are peptide mimics named “peptoids”. Their efficient synthesis employs primary amines, enabling the incorporation of metal binding side chains, with a rationally designed specific sequence. Thus, peptoid-metal complexes can be obtained and used for catalysis.

In this study, different trimeric peptoid-cobalt complexes were synthesized, characterized and their electrocatalytic activity was investigated. These complexes are active in neutral pH and exhibit a fairly low overpotential (η=730 mV) in phosphate buffer. Moreover, by altering the metal-binding ligand of the peptoid, the catalytic properties are changed, indicating the significance of the organic ligands to the reactivity of the catalyst and enabling a tuning method of it.