Ambient\nAir-Synthesized CsPbBr<sub>3</sub> Nanocrystals\nCoupled with TiO<sub>2</sub> Film as an Efficient Hybrid Photoanode\nfor Photoelectrochemical Methanol-to-Formaldehyde Conversion

Due\nto its exceptional optoelectronic properties in the visible\nspectrum, cesium lead bromide (CsPbBr<sub>3</sub>) perovskite has\nattracted considerable attention in solar-driven organic transformations\nvia photoelectrochemical (PEC) cells. However, the performance of\nthe devices is adversely affected by electron–hole recombination\noccurring between a transparent conductive substrate, such as fluorine-doped\ntin dioxide (FTO), and a perovskite layer. Herein, to mitigate this\nissue, a compact layer of titanium dioxide (TiO<sub>2</sub>) was employed\nas both an electron transport layer and a hole blocking layer to diminish\ncharge recombination while facilitating electron transfer in such\nperovskite material. At the oxidation peak potential of 0.70 V vs\nAg/AgNO<sub>3</sub>, a hybrid photoanode of CsPbBr<sub>3</sub>/TiO<sub>2</sub>/FTO exhibited a significant increase in photocurrent density,\nfrom 15 to 41 μA/cm<sup>2</sup>, compared to a configuration\nwithout a TiO<sub>2</sub> layer. Furthermore, the introduction of\nmethanol as a hole scavenger in the PEC system using the hybrid photoanode\nfacilitated the separation of electron–hole pairs, which led\nto an enhanced photocurrent density of 60 μA/cm<sup>2</sup> and\npromoted the production of formaldehyde. High-performance liquid chromatography\n(HPLC) confirmed the generation of formaldehyde at a concentration\nof 26.69 μM with a Faradaic efficiency of 92% under an applied\npotential of 0.50 V vs Ag/AgNO<sub>3</sub> for 60 min of PEC reaction.\nIn addition to the enhanced PEC performance achieved from this hybrid\nphotoanode, CsPbBr<sub>3</sub> nanocrystals (NCs) in this work were\nsynthesized by the modified one-pot method under ambient air, where\nhighly uniform and high-purity NCs were obtained. This work signifies\nthe groundbreaking exploration of CsPbBr<sub>3</sub> NCs with TiO<sub>2</sub> as a photoelectrode material in the organic-based PEC cells,\nwhich efficiently improved the interfacial charge transfer within\nthe photoanode for the conversion of methanol to formaldehyde, marking\na significant advancement in the field.