Defect Stability of IrO2 (110) Under Acidity and Anodic-Bias

Dissolution of Ir is recognized as the main driving force of the stability issue for the state-of-the-art IrO₂ catalyst working under acidic conditions with anodic bias. However, a critical understanding of the lattice defects in IrO₂ bulk and its surface that drives the Ir dissolution is lacking, probably due to the difficulty of experiments to quantify the points defects in a single-crystal oxides with a well-defined surface. Here we use a computational approach, i.e. a first-principles based calculations of defect energy in combination of the classical thermodynamic model under the real electrochemical environment, to resolve the defect stability within IrO₂ that eventually drives the structure collapse. We started with applying the standard and simple computational hydrogen electrode (CHE) approach, where electron and proton transfers are always coupled, to the bulk lattice defect of IrO₂and constructed the bulk defect Pourbaix diagram. Then we moved on to the (110) surface and considered the relevant electrochemical factors including the electrode surface solvation and charging, and the dielectric and ionic response from the electrolyte. A detailed mapping of the surface defect stability w.r.t the applied electrode potential and pH were obtained. The computational study is reported to our experimental collaborators and asks for experimental evidence.