Positive Feedback Mechanism of Stability Degradation of the IrO2/TiO2 Electrocatalyst Induced by Inferior Catalytic Activity

Iridium (Ir)-based catalysts embracing both catalytic activity and stability are of great significance for scaling up the application of proton exchange membrane water electrolysis (PEMWE). Herein, supported IrO2 on TiO2 (IrO2/TiO2) with high specific surface area and electrolytic activity was prepared by adopting a chlorine (Cl)-free synthesis based on the Adams fusion method. The crucial influential factors of annealing temperature were systematically explored on the catalytic activity and stability of IrO2/TiO2. Although increasing annealing temperature is believed to be of benefit to the increase of crystallinity and nanoparticle size in the catalyst, thus improving the stability of the catalyst, the as-prepared catalyst annealed at high temperature exhibited inferior stability at a constant-current density working state. This result is mainly attributed to the adverse impact of the annealing process at high temperatures on the catalytic activity, in terms of decreasing the active surface area due to the aggregation effect and decreasing the intrinsic activity due to the formation of a highly crystalline structure. The inferior catalytic activity caused by the adverse impact can induce a large working voltage, which can accelerate the catalyst degradation via a positive feedback mechanism (PFM) beneath the electrocatalytic system consisting of 'catalytic activity–electrocatalytic performance (working voltage)–aging'. Besides, the influences of Cl residue on the catalytic activity and stability of the as-prepared IrO2/TiO2 were also investigated by substituting a Cl-free precursor using IrCl3 (IrO2/TiO2–Cl). It presented slightly inferior initial oxygen evolution reaction (OER) electrocatalytic performance to that using a Cl-free precursor, perhaps due to the strong adsorption of Cl residue on IrO2 nanoparticles. However, the stability of the as-prepared IrO2/TiO2–Cl deteriorates significantly in chronopotentiometric measurement probably due to the PFM. Consequently, catalytic activity and stability are of equal significance; both the annealing temperature and Cl residue need to be fine-tuned to achieve an optimal combination of catalytic activity and stability.