Understanding the Role of Cr in Au Supported CoOx for Electrochemical Water Oxidation

Abstract

Oxygen evolution reaction (OER) remains the biggest chemical bottleneck in commercial application of electrochemical H2 production. Developing affordable, stable, and efficient catalysts requires systematic understanding of mechanistic pathways. In situ studies have increasingly become important towards solving this chemical bottleneck. Cobalt oxides have been reported as promising water oxidation anodes. Mixed metal oxides are interesting materials for heterogeneous catalysis as the valence state of individual metal cations can be tuned, affecting the catalytic activity. Cobalt oxide catalysts have been improved by addition of heteroatoms such as Fe and Ni.Herein, we have reported significant increase in activity of deposited (electroless) Cobalt oxide catalysts by addition of Cr. We have used Raman Spectroscopy to track the development of catalyst in situ. Our results showed that catalyst layers essentially develop in situ. Presence of Cr affects the redox behaviors of Cobalt oxides. Co[Cr]Ox/Au samples showed significantly high pre-OER oxidation features and reduced OER onset potential by ~150 mV. In situ spectroscopy showed that presence of Cr tends to stabilize the lower oxidation states of Co. At the OCP, Co[Cr]Ox/Au samples showed significant amounts of Co2+ species compared to pure CoOx/Au. Under conditions of OER, CoOx/Au showed significant amounts of Co4+ {CoO2} species whereas no such species were seen in the Cr containing sample, Co[Cr]Ox/Au. Using in situ studies, we could correlate the formation of a metastable Au-OOH species with the onset potential of OER, indicating that Au is intimately involved in the reaction mechanism of OER.Reference: Das, A; Mohapatra, B; Kamboj, V; Ranjan, C. ChemCatChem 2021, 13, 1 –12. DOI : 1002/cctc.202001889 Figure 1