Improving the electrocatalytic activity of cobalt oxide with bismuth for acidic oxygen evolution reaction

Abstract

Highly durable, low-cost electrocatalysts for acidic oxygen evolution reaction (OER) are very essential for the commercial success of proton exchange membrane-based water electrolysis. The catalysts currently available for this reaction are mainly based on noble metals such as iridium (Ir) and ruthenium (Ru), which are notoriously unstable under acidic OER conditions, besides their high cost. Herein, we demonstrate that the incorporation of the main group metal bismuth (Bi) in cobalt oxide improves the latter's overall catalytic activity towards acidic OER without reducing its stability. Among the Bi-doped cobalt oxide catalysts synthesized with different Co : Bi ratios, the one with a Co : Bi ratio of 9 : 1, denoted Co₉BiO_x, exhibits the best performance with an overpotential of 540 mV at the current density of 10 mA cm⁻² at pH 1. This catalyst is also reasonably stable for about 45 hours while driving the reaction at a current density of 5 mA cm⁻². X-ray photoelectron spectroscopic studies and density functional theory-based calculations indicate that the Bi sites in these materials are catalytically active for acidic OER. In addition, the versatility of Bi in enhancing the catalytic activity of transition metal oxides towards acidic OER is demonstrated with Bi-doped iron oxides and nickel oxides.