Hydrogen is considered to be a cleaner and sustainable energy alternative for the present carbon based petroleum fuels. If the electricity is generated in a renewable fashion, water electrocatalysis is an efficient way of hydrogen production. The current problem with this is that it uses rare and expensive materials like Pt as electrodes, which makes large-scale deployment seemingly very expensive. Research into more advanced materials has been of interest for the past few decades. Transition metal oxides for this purpose have been reported in many occasions as alternatives for expensive metals. Among them, cobalt oxide, which was reinvented by Nocera <i>et al</i>., has attracted much interest because of its stability, ease of preparation, and its efficiency at neutral pH. This catalyst is proposed to consist of cubane shaped motifs. Very recently, many other catalyst complexes with cobalt cubane motifs have also been reported.<br/>We have investigated the cobalt oxide catalysts with two cluster models. Based on experimental evidence, we modeled a minimum structural requirement of a cobalt dimer and a dimer of dimers in a cubane fashion. The resting state of the catalyst was modeled with Co(III) centers coordinated with octahedral geometry. We employed the B3LYP/KTZVP level of theory and extensively investigated possible reaction mechanisms that potentially can be promoted by these two cluster models. With our first principles calculations of the cobalt dimer complex we have observed that the lowest energy pathway proceeds through a geminal dehydrogenation of a μ-hydroxo moiety. The lowest energy pathway from the cubane core is a nucleophilic attack of a solvent water molecule to a Co(V)-O surface radical group.

Insights into cobalt oxide water oxidation catalysts: A theoretical perspective from model dimer and cubane complexes

249th National Meeting (2015)

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