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.