Acetaldehyde Production via Photocatalytic Heterolytic Dehydrogenation of Ethanol Accelerated by Tuning Lewis Acid–Base Pairs over CsGeX₃ (X = Cl, Br, I) Halide Perovskites

Photocatalytic hydrogen (H2) production from ethanol offers the dual advantages of low energy consumption and the cogeneration of high-value chemicals. However, challenges remain in enhancing product selectivity and elucidating the precise reaction pathway. In this study, lead-free halide perovskites CsGeX3 (X = Cl, Br, I) were synthesized and utilized for the simultaneous generation of H2 and acetaldehyde via photocatalytic ethanol oxidation under UV and visible light irradiation. Among them, CsGeI3 is reported for the first time as a highly effective photocatalyst, exhibiting the highest activity for both the hydrogen evolution reaction (HER) and the ethanol oxidation reaction (EOR). Under UV light irradiation for 3 h, CsGeI3 achieves H2 and acetaldehyde yields of 97.74 and 92.08 μmol g– 1, respectively, with an apparent quantum yield (AQY) of 2.31% for H2. Optical characterization and density functional theory (DFT) calculations revealed that the Lewis acid–base properties of CsGeI3 are mainly governed by the halogen component, enabling the selective activation and cleavage of the α-C–H and O–H bonds in ethanol, promoting heterolytic reactions that enhance the formation of both H2 and acetaldehyde. This study provides new insights into the application of lead-free halide perovskites in tunable solar fuel generation and selective value-added chemical synthesis.