Iridium-Based Materials as an Electrocatalyst in Computational Investigation of Their Performance for Hydrogen and Oxygen Evolution Reactions

Electrocatalytic water splitting, a process that converts water into hydrogen and oxygen, underpins the development of sustainable and carbon-neutral energy systems. Despite substantial progress, there remains an incomplete atomistic understanding of the mechanisms by which noble-metal catalysts lower reaction overpotentials, thus hampering the rational design of cost-effective alternatives. In this study, we use density functional theory calculations in combination with the computational hydrogen electrode model to explore the catalytic properties of metallic iridium and its oxides (IrO2 and Ir2O3) on various crystallographic surfaces concerning the hydrogen and oxygen evolution reactions. The analysis indicates that variations in the oxidation state and surface coordination profoundly influence the adsorption energetics and catalytic efficacy. Among the investigated systems, IrO2 surfaces exhibit optimal adsorption energies for oxygen evolution intermediates, resulting in low overpotentials while maintaining moderate hydrogen evolution activity. In contrast, metallic Ir and Ir2O3(0001) facets display hydrogen evolution reaction activity comparable with pure Ir, yet their oxygen evolution reaction performance is hampered by the excessive stabilization of intermediates. The Ir2O3(101̅0) surface binds intermediates too strongly, leading to suboptimal activity for both reactions. Additionally, the preferred adsorption sites and charge-transfer characteristics are seen to vary significantly with surface termination, directly affecting the thermodynamics of intermediate formation. Together, these findings elucidate the interaction between surface structure, oxidation state, and electronic properties in dictating the electrocatalytic performance of iridium-based materials, providing valuable insights into the rational design of advanced catalysts for water splitting.