Theoretical Prediction and Experimental Verification of IrOx Supported on Titanium Nitride for Acidic Oxygen Evolution Reaction

Reducing iridium (Ir) catalyst loading for acidic oxygen evolution reaction (OER) is a critical strategy for large-scale hydrogen production via proton exchange membrane (PEM) water electrolysis. However, simultaneously achieving high activity, long-term stability, and reduced material cost remains challenging. To address this challenge, we develop a framework by combining density functional theory (DFT) prediction using model surfaces and proof-of-concept experimental verification using thin films and nanoparticles. DFT results predict that oxidized Ir monolayers over titanium nitride (IrO_x/TiN) should display higher OER activity than IrO_x while reducing Ir loading. This prediction is verified by depositing Ir monolayers over TiN thin films via physical vapor deposition. The promising thin film results are then extended to commercially viable powder IrO_x/TiN catalysts, which demonstrate a lower overpotential and higher mass activity than commercial IrO₂ and long-term stability of 250 h to maintain a current density of 10 mA cm^-2. The superior OER performance of IrO_x/TiN is further confirmed using a proton exchange membrane water electrolyzer (PEMWE), which shows a lower cell voltage than commercial IrO₂ to achieve a current density of 1 A cm^-2. Both DFT and in situ X-ray absorption spectroscopy reveal that the high OER performance of IrO_x/TiN strongly depends on the IrO_x-TiN interaction via direct Ir-Ti bonding. This study highlights the importance of close interaction between theoretical prediction based on mechanistic understanding and experimental verification based on thin film model catalysts to facilitate the development of more practical powder IrO_x/TiN catalysts with high activity and stability for acidic OER.