Interfacial Regulation by a NiOₓ Overlayer Enables Enhanced Near-Infrared Photoelectrochemical Water Splitting

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Photoelectrochemical (PEC) water splitting provides a promising pathway for sustainable hydrogen production. However, the inefficient use of near-infrared (NIR) light, which accounts for nearly half of the solar spectrum, remains a major limitation to overall energy conversion efficiency. Here, we present a NIR-responsive dye-sensitized photoanode enabled by a boron–dipyrromethene–carbazole-based organic sensitizer (1), combined with a thin NiOₓ overlayer that acts as both an oxygen evolution reaction (OER) cocatalyst and an interface regulator. The NiOₓ layer, deposited via low-temperature pulsed laser deposition, exhibits low crystallinity and mixed Ni2+/Ni3+ valence states, as confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. Adding the NiOₓ overlayer results in a 1.9-fold increase in photocurrent density and significantly better photostability. Electrochemical testing indicates that NiOₓ alters interfacial charge–transfer kinetics and the local electrochemical environment, thereby improving carrier utilization and reaction efficiency. The multilayer photoanode retains a measurable photocurrent response at 850 nm, demonstrating its capability to extend PEC activity into the NIR region. This work elucidates the synergistic functions of NiOₓ in interfacial charge regulation and catalytic kinetics, offering a viable strategy for NIR-driven solar fuel conversion. Additionally, it establishes the longest-wavelength photoelectrocatalytic performance reported to date for non-noble-metal dye-sensitized systems.

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