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

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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.

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