Unraveling the stability and coverage-dependent OER activity of antimony oxide phases: a surface Pourbaix perspective

Abstract

Deciphering the catalytic potential of antimony (Sb) and antimony oxides (SbxOy) requires fundamental understanding of their surfaces under the oxidative conditions of the oxygen evolution reaction. Using DFT calculations we constructed surface Pourbaix diagrams for Sb(012), (1 - Sb2O3(121), alpha - SbO2(112), and Sb2O5(11- 1) surfaces, mapping their potential-pH equilibria. While Sb and Sb2O3 exhibit broad potential-pH stability, Sb2O5 is restricted to acidic media, and SbO2 is prone to aqueous decomposition. We reveal a coverage-dependent activity crossover: Sb2O5 excels at low coverage (eta = 0.45 V), whereas (1 - Sb2O3 outperforms (eta = 0.63 V) under high-coverage, "self-consistent" conditions. This study establishes thermodynamic framework for designing robust SbxOy catalysts.