Regulating Metal-Support Interaction via WO3 Crystal Phase Engineering for Enhanced Acidic Water Oxidation.

Metal-support interaction (MSI) is pivotal in tuning the intrinsic activity and structural stability of heterogeneous catalysts, yet precise control of MSI strength remains a major challenge. Herein, we demonstrate crystal-phase engineering of WO3 supports-monoclinic (M-WO3), orthorhombic (O-WO3), and tetragonal (T-WO3)-to modulate MSI in Ir single-atom catalysts. The three WO3 crystals exhibit distinct distortion degrees (M-WO3 > O-WO3 > T-WO3), where stronger distortion enhances Ir activity but compromises stability. Notably, O-WO3 achieves an optimal modulation balance: the moderate W─O bond strength and distortion induce the strongest MSI, elevating the Ir oxidation state to +5.74, shortening the Ir─O bond, and reinforcing Ir─O covalency. Such favorable electronic and structural modulation substantially promotes intrinsic oxygen evolution reaction (OER) activity. The O─WO3─Ir catalyst exhibits a low overpotential of 219 mV at 10 mA cm-2 and demonstrates outstanding acidic OER stability, with a cumulative operation time over 1000 h under sequential testing at different current densities. The optimized MSI promotes high-valence Ir formation, accelerates *OO intermediate generation, and suppresses Ir dissolution, thereby addressing sluggish kinetics and unstable active sites. This work provides new insights into regulating MSI strength via crystal-phase engineering to advance durable and efficient acidic OER catalysts.