Molecular Coordination Programs Coupled Vacancies in PbCrO4 Photoanodes for Photoelectrochemical Water Splitting

Photoelectrochemical water splitting requires photoelectrodes that combine highly ordered crystalline frameworks with controlled point-defect chemistry, efficient charge transfer and utilization. However, solution-based crystal growth often produces uncontrolled point-defect populations, making it challenging to construct coupled-vacancy configurations within a crystalline lattice. Herein, we report a molecular‑coordination strategy employing the ionic‑liquid 1‑butyl‑3‑methylimidazolium tetrafluoroborate ([BMIM]BF4) to modulate Pb2+ precursor coordination and redirect the crystallization pathway of PbCrO4. Coordination-mediated reshaping of the nucleation energy landscape drives rapid single-phase crystallization of PbCrO4 and preferentially induces the formation of surface-enriched coupled Pb-O vacancy configurations. These coupled vacancy motifs reorganize the near-surface electronic structure and alter the energetic distribution of surface defect states, thereby promoting interfacial hole injection and charge utilization. Compared with the photoanode prepared without [BMIM][BF4], the ionic‑liquid modified PbCrO4-IL photoanode exhibits a 3.4-fold enhancement in photocurrent density, increasing from 1.1 to 3.7 mA cm-2 under identical conditions. The optimized NiFeCoOx‑decorated photoanode further delivers a photocurrent density of 4.05 mA cm-2 at 1.23 V vs. RHE under AM 1.5 G simulated sunlight, reaching an applied‑bias photon‑to‑current efficiency (ABPE) of 1.65%. This work demonstrates molecular coordination as an effective route to program synergistic vacancy architectures in oxide semiconductors for photoelectrochemical energy conversion.