2D/2D BiVO4/CsPbBr3 S-scheme heterojunction for photocatalytic CO2 reduction: Insights into structure regulation and Fermi level modulation

Heterojunction construction is a universal and effective approach to achieve high-efficiency photocatalysts. Towards these well-designed heterojunctions, modulation on steering dynamic charge transfer holds great promise in further performance stimulation. Herein, 2D/2D BiVO4/CsPbBr3 S-scheme heterojunctions, of which CsPbBr3 nanosheets (NSs) are in-situ face-to-face grown onto BiVO4 NSs, are designed as cornerstones for further carrier managements. Briefly, with controllable heterostructure regulation, an intimate heterointerface between BiVO4 and CsPbBr3 NSs with similar size can be obtained accompanied with a maximally intensified interfacial interaction, largely boosting charge transfer across the interfacial conjunction. Moreover, by further tailoring the intrinsic O vacancy (VO••) of BiVO4, the gradient Fermi level shift towards its valence band is finely tuned, yielding an enlarged Fermi level gap and an enhanced internal electric field (IEF) over BiVO4/CsPbBr3 heterojunctions. Such an intensified IEF provides a powerful driving force for directional charge migration, resulting in high charge separation and utilization efficiency. Hence, the optimized BiVO4/CsPbBr3 S-scheme heterojunction features desirable accelerated dynamic carrier mobility, delivering comparably high CO2-to-CO conversion with a turnover number (TON) near 230 without any co-catalyst or sacrificial agent. The accelerated S-scheme charge transfer mechanism is revealed in detail by X-ray photoelectron spectroscopy (XPS), theoretical calculations, photo-irradiated Kelvin probe force microscopy and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).