Stability and Activity of Cobalt Antimonate for Oxygen Reduction in Strong Acid

Guided by computational Pourbaix screening and high-throughput experiments aimed at the development of precious-metal-free fuel cells, we investigate rutile CoSb₂O₆ as an electrocatalyst for oxygen reduction in 1 M sulfuric acid. Following 4 h of catalyst conditioning at 0.7 V vs RHE, operation at this potential for 20 h yielded an average current density of -0.17 mA cm^-2 with corrosion at a rate of 0.04 nm hour^-1 that is stoichiometric with catalyst composition. Surface Pourbaix analysis of the (111) surface identified partial H coverage under operating conditions. The Sb active site has an HO^∗ binding free energy of 0.49 eV, which is near the peak of the kinetic 4e^- ORR volcano for transition-metal oxides in acidic conditions. The experimental demonstration of operational stability and computational identification of a reaction pathway with favorable energetics place rutile CoSb₂O₆ among the most promising precious-metal-free electrocatalysts for oxygen reduction in acidic media.