Mechanism Modeling and Structural Investigation of Spinel Oxides as a Catalyst for Oxygen Evolution Reaction

Water electrolysis is a well-established method to produce hydrogen from the renewable energy sources. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are the two important processes that are involved in electrochemical water splitting process that, in case of large-scale, is greatly hindered by the sluggish anodic OER. Spinel oxides (AB2O4) are promising non-noble catalyst materials that needs further study in this field. Using density functional theory (DFT), Nickel ferrite, NiFe2O4, and Cobalt ferrite, CoFe2O4, were extensively investigated, and the mechanism and energetics of OER with wide set of intermediates and mechanistic pathways along with critical (rate-determining) O-O bond formation barriers and transition-state structures were quantitatively modelled as the first comprehensive study on selected spinel oxides in the literature. Moreover, expanding the work, the surface structures of the low-index facets of a set of spinel oxides (NiFe2O4, CoFe2O4, NiCo2O4, ZnCo2O4) were investigated with periodic DFT+U calculations under following conditions: bare surfaces under vacuum, and adsorbate-covered facets for CoFe2O4 under OER. The plausible surface configurations as candidates for both resting and intermediate states under different conditions were derived and this information were used to build optimal nanoparticle shape via the Wulff construction, fulfilling the goal of prediction of nanoparticle shape and ordering under operating conditions. Core Level Shift (CLS) simulations were also performed to provide a link between the binding energy measured in photoemission experiments and the atomistic bonding models.