Modulation of the Electronic Properties of Co₃O₄ through Bi Octahedral Doping for Enhanced Activity in the Oxygen Evolution Reaction

Developing a highly active and stable electrocatalyst for the oxygen evolution reaction (OER) is essential for efficient hydrogen production through anion exchange membrane water electrolysis powered by renewable electricity. Recently, there has been a renewed interest in designing electrocatalysts based on their work function optimization. The insights into the materials' electronic properties gained from developing other heterogeneous catalysts, such as those used for N₂O decomposition, can be thus leveraged to enhance the performance of the OER electrocatalysts. Knowing that Bi enhances the catalytic activity of Co₃O₄ in N₂O decomposition, where the surface electronic properties play a crucial role, we hypothesized that it might also improve the electroactivity of the OER electroactivity. Therefore, we synthesized Bi-doped Co₃O₄ with different bismuth contents and studied the sample with a complementary set of physicochemical, electrochemical, and computational techniques. We found that promoting Co₃O₄ with atomically dispersed bismuth enhances its OER electrocatalytic properties by reducing the energy of the potential-determining step and improving electron charge transfer properties. Bismuth atoms enter octahedral sites in Co₃O₄, creating Bi active centers and enhancing the activity of vicinal Co sites in the OER. The Bi and modified Co centers are characterized by increased binding energy of the intermediate state of the metal-oxygen intermediate and increased density of states at the Fermi level. The former reduces the overpotential required for the OER, whereas the latter improves the reaction kinetics by decreasing the charge transfer resistance.