Defect phase in rutile IrO2 under OER condition

IrO₂ is the only candidate material for green hydrogen production through acidic water electro-splitting, due to its sufficient activity and stability under the harsh acidic and anodic conditions. However, overlong operation can gradually degrade the material with Ir dissolution to the liquid electrolyte solution. Similarly, lattice oxygen is also found to be able to participate in the redox process and leave the oxide lattice. IrO2 is shown as ultra-stable phase in the bulk Pourbaix diagram, e.g. at pH=1, it can sustain itself against fully dissolution up to U~2.0 V. However, experiments do find Ir species in the liquid solution, as well as lattice O species in the bubbling O2 gas through isotope mass spectrometry, atom probe, and titration within the bulk phase stability window. This comes to the question: Is the bulk Pourbaix missing any information capturing that or is it due to the defect in experimental samples? Theoretically, the bulk Pourbaix diagram always assumes line-compounds of all solid phases, excluding the possibility of introducing intrinsic lattice defects. This ignores the potential solubility or tolerance of lattice with its own defects, e.g. vacancies. In this talk, I will show you how we reconstruct the electrochemical stability diagram, by allowing the rutile lattice incorporating vacancies on both Ir and O sub-lattices. Through a statistical thermodynamic approach, we are able to generate the grand potential landscape of Ir1-xO2-y at any given pH and U. Both microscopic and macroscopic thermodynamic analysis of the defect phase stability will be given, with a conclusion drawn on how defect phase serves as the tunnel for phase stabilization, amorphization and dissolution.