Regulating Electronic Structure of Sub-2 nm IrO 2 Nanocrystals with N Atoms for Enhanced Acidic Oxygen Evolution Performance

One of the key factors hindering the commercial application of proton exchange membrane water electrolysis is the high cost and low performance of anodic Ir-based electrocatalysts. Here we report an excellent Ir-based electrocatalyst consisting of sub-2 nm IrO2 nanocrystals (NCs) attached to porous $N$-doped carbon supports $\left(S N-I r O_{2} / P N C\right)$, exhibiting a high oxygen evolution reaction (OER) activity with a low overpotential of $259 \text{mV}\left(10 \text{mA} \cdot \text{cm}^{-2}\right)$ and high mass activity of $2.936 \text{mA} \cdot \mu_{g_{I r}}{ }^{-2}$ at an overpotential of 300 mV and excellent stability of $20 h$ in acidic electrolytes. The formation of sub-2 nm $\text{IrO}_{2} \text{NCs}$ with an average size of about 1 nm is mainly attributed to the porosity of the $N$-doped carbon substrate. Physicochemical characterization results show that the introduction of $N$ atom plays an important role in regulating the electronic structure of sub-2 nm IrO2 NCs, which is conducive to improving the catalytic performance. Density functional theory calculations reveal that the adsorption of the active site Ir to the intermediate oxygen-containing species is weakened after the introduction of $N$ atom into the carbon support, thus reducing the reaction free energy of the rate-determining step toward OER.