Regulating Ir−O Covalency to Boost Acidic Oxygen Evolution Reaction

Abstract

The unsatisfactory oxygen evolution reaction (OER) activity of IrO2 has intensively raised the cost and energy consumption of hydrogen generation from proton exchange membrane water electrolyzers. Here, the acidic OER activity of the rutile IrO2 is significantly enhanced by the incorporation of trivalent metals (e.g., Gd, Nd, and Pr) to increase the Ir−O covalency, while the high-valence (pentavalent or higher) metal incorporation decreases the Ir−O covalency resulting in worse OER activity. Experimental and theoretical analyses indicate that enhanced Ir−O covalency activates lattice oxygen and triggers lattice oxygen-mediated mechanism to enhance OER kinetics, which is verified by the finding of a linear relationship between the natural logarithm of intrinsic activity and Ir−O covalency described by charge transfer energy. By regulating the Ir−O covalency, the obtained Gd-IrO2–δ merely needs 260 mV of overpotential to reach 10 mA cm−2 and shows impressive stability during a 200-h test in 0.5 м H2SO4. This work provides an effective strategy for significantly enhancing the OER activity of the widely used IrO2 electrocatalysts through the rational regulation of Ir−O covalency.