Strain-Triggered Distinct Oxygen Evolution Reaction Pathway in Two-Dimensional Metastable Phase IrO 2 via CeO 2 Loading.

A strain engineering strategy is crucial for designing a high-performance catalyst. However, how to control the strain in metastable phase two-dimensional (2D) materials is technically challenging due to their nanoscale sizes. Here, we report that cerium dioxide (CeO 2 ) is an ideal loading material for tuning the in-plane strain in 2D metastable 1T-phase IrO 2 (1T-IrO 2 ) via an in situ growth method. Surprisingly, 5% CeO 2 loaded 1T-IrO 2 with 8% compressive strain achieves an overpotential of 194 mV at 10 mA cm -2 in a three-electrode system. It also retained a high current density of 900 mA cm -2 at a cell voltage of 1.8 V for a 400 h stability test in the proton-exchange membrane device. More importantly, the Fourier transform infrared measurements and density functional theory calculation reveal that the CeO 2 induced strained 1T-IrO 2 directly undergo the *O-*O radical coupling mechanism for O 2 generation, totally different from the traditional adsorbate evolution mechanism in pure 1T-IrO 2 . These findings illustrate the important role of strain engineering in paving up an optimal catalytic pathway in order to achieve robust electrochemical performance.