Ambient Air-Synthesized CsPbBr₃ Nanocrystals Coupled with TiO₂ Film as an Efficient Hybrid Photoanode for Photoelectrochemical Methanol-to-Formaldehyde Conversion

Due to its exceptional optoelectronic properties in the visible spectrum, cesium lead bromide (CsPbBr₃) perovskite has attracted considerable attention in solar-driven organic transformations via photoelectrochemical (PEC) cells. However, the performance of the devices is adversely affected by electron-hole recombination occurring between a transparent conductive substrate, such as fluorine-doped tin dioxide (FTO), and a perovskite layer. Herein, to mitigate this issue, a compact layer of titanium dioxide (TiO₂) was employed as both an electron transport layer and a hole blocking layer to diminish charge recombination while facilitating electron transfer in such perovskite material. At the oxidation peak potential of 0.70 V vs Ag/AgNO₃, a hybrid photoanode of CsPbBr₃/TiO₂/FTO exhibited a significant increase in photocurrent density, from 15 to 41 μA/cm², compared to a configuration without a TiO₂ layer. Furthermore, the introduction of methanol as a hole scavenger in the PEC system using the hybrid photoanode facilitated the separation of electron-hole pairs, which led to an enhanced photocurrent density of 60 μA/cm² and promoted the production of formaldehyde. High-performance liquid chromatography (HPLC) confirmed the generation of formaldehyde at a concentration of 26.69 μM with a Faradaic efficiency of 92% under an applied potential of 0.50 V vs Ag/AgNO₃ for 60 min of PEC reaction. In addition to the enhanced PEC performance achieved from this hybrid photoanode, CsPbBr₃ nanocrystals (NCs) in this work were synthesized by the modified one-pot method under ambient air, where highly uniform and high-purity NCs were obtained. This work signifies the groundbreaking exploration of CsPbBr₃ NCs with TiO₂ as a photoelectrode material in the organic-based PEC cells, which efficiently improved the interfacial charge transfer within the photoanode for the conversion of methanol to formaldehyde, marking a significant advancement in the field.