Universal Interfacial Engineering via Amorphous Inorganic Binders: Passivating Surface States and Accelerating Hole Transfer across Metal Oxide Photoanodes in Photoelectrochemical Water Oxidation

High Resolution Image Download MS PowerPoint Slide Interfacial engineering of photoanodes is essential for efficient solar water splitting; however, many existing strategies rely on complex, multistep processes or hydrothermal growth, limiting scalability and reproducibility. Here, we present a universal interfacial engineering platform based on a sub-2 min acidic redox-assisted deposition (ARD) of an amorphous inorganic binder, cobalt–manganese oxyhydroxide (CMOH). Using two-step-fabricated BiVO 4 as a literature-standard benchmark, we demonstrate that an ultrathin CMOH overlayer markedly enhances photoelectrochemical (PEC) water oxidation performance. The conformal CMOH coating (∼3.5 nm) is deposited under ambient conditions via a simple dip-coating process and is broadly applicable to metal oxide photoanodes, including BiVO 4, WO 3, and ZnO. The CMOH-modified BiVO 4 photoanode delivers a high photocurrent density of ∼6.0 mA cm –2 and a hole-transfer efficiency of ∼82% at 1.23 V RHE, together with a remarkable applied bias photon-to-current efficiency (ABPE) of 1.68% at 0.66 V RHE . These enhancements originate from effective surface-state passivation by the CMOH overlayer, leading to over a 4-fold reduction in the surface recombination rate constant, as revealed by intensity-modulated photocurrent spectroscopy (IMPS). In addition, the reduced Tafel slope (78.5 mV dec –1 ) suggests that the CMOH layer promotes interfacial charge transfer and enhances the water oxidation kinetics of the BiVO 4 photoanode. This work elucidates the critical role of amorphous CMOH oxygen evolution catalysts in mediating photoinduced charge-carrier dynamics and establishes a facile and scalable strategy to broadly enhance the PEC performance of metal oxide photoanodes for large-scale solar fuel production.