Facet- and Graphene-Support-Dependent Activity of Ta2O5 for Oxygen Evolution Reaction

Abstract

Ta2O5 is among the few metal oxides that are stable in acidic media, but, due to its insulating nature, its use in electrocatalytic oxygen evolution reaction (OER) has been less explored. Herein, density functional theory calculations were performed on three different Ta2O5 facets, pristine and with O or Ta defects. The goal was to identify strategies to improve the OER performance of Ta2O5 by establishing correlations with its intrinsic properties. The study revealed that the OER activity of Ta2O5 is facet-dependent according to the following trend (200) > (120) > (001), which correlated with the Ta density on the topmost atomic layer. The lowest overpotential, 0.61 V, was observed at the Ta-O site of the pristine (200) facet, followed by a Ta site on the same facet with a Ta defect (0.63 V). The moderate density of states (DOS) at the Fermi level and lower Ta site density on the (200) surface contributed to its higher performance compared to other facets. The correlation analysis conducted by considering Bader charge, d-band analysis of Ta sites, and valence electrons showed strong correlations for (120) surfaces, whereas (200) surfaces had moderate correlations. As a conductive phase is often added to insulating materials in experiments, the (200) Ta2O5/graphene heterostructure was also studied. An overpotential as low as 0.39 V was found for the Ta-O sites of the heterostructure. According to the partial DOS analysis, the improved OER performance of the heterostructure can be attributed to the shift in the d orbitals of Ta sites toward lower energies and the increase in the DOS intensity. This study offers valuable insights for designing Ta2O5-based electrocatalysts for OER in acidic media.