Construction of Bi Nanoparticles Loaded BiOCl Nanosheets Ohmic Junction for Photocatalytic CO<sub>2</sub> Reduction

Abstract: The continuous increase in the consumption of coal, oil, and natural gas has not only led to the depletion of unsustainable energy sources, but has also caused excessive CO2 emissions, thus resulting in serious energy crises and climate issues. In such a scenario, it is imperative to explore clean and sustainable energy conversion technologies to address the escalating energy demands and environmental crises. Photocatalytic CO2 conversion, inspired by natural photosynthesis, utilizes solar energy to convert CO2 and water into valuable chemicals. After decades of development, artificial photosynthesis has emerged as a green, cost-effective, and sustainable approach to achieving carbon neutrality. However, the challenges of low carrier separation efficiency and insufficient active sites in photocatalysts remain significant hurdles in achieving high-performance CO2 photoreduction. To address this challenge, the integration of metal nanoparticles with semiconductors to create an Ohmic junction can enhance electron-hole migration by the assist of interfacial electric field (IEF). In this study, an Ohmic junction photocatalyst is constructed by in situ formation of Bi nanoparticles on the surface of BiOCl nanosheets through a solvothermal process. The composition and morphology of the photocatalysts were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) was employed to assess the light absorption performance of the photocatalyst. Transient photocurrent response, electrochemical impedance spectroscopy (EIS), and electron spin resonance (ESR) were utilized to evaluate the efficiency of electron-hole transfer. The distinct work function difference between Bi nanoparticles and BiOCl nanosheets leads to favorable charge transfer characteristics within the formed Ohmic junction, significantly improving the utilization efficiency of photogenerated carriers. Besides, the Bi nanoparticles serve as co-catalysts, enhancing the activation of inert CO2. As a result, the optimized Bi/BiOCl composite (Bi/BiOCl-2) exhibits enhanced generation rates of CO (34.31 µmol∙g−1) and CH4 (1.57 µmol g−1) during 4-hours of irradiation, which is 2.55 and 4.76 times compared to pristine BiOCl nanosheets, respectively. Isotope tracer experiments suggest that the obtained carbon-based products are generated through CO2 photoreduction in the presence of water molecule under irradiation. Moreover, in situ Fourier-transform infrared spectroscopy (in situ FTIR) results indicate the formation of *CHO, *CH3O, b-CO32−, m-CO32−, HCO−3, HCOOH, *COOH, and HCOO− species during the CO2 reduction process and a possible mechanism for CO2 photoreduction into CO and CH4 is proposed based on these findings. After 25-hours of CO2 photoreduction reaction, the yields of CO and CH4 continue to increase. Furthermore, the stability of the prepared material is confirmed by XRD pattern, XPS analysis, and TEM image. These outcomes underscore an effective strategy for constructing advanced photocatalysts tailored for high-performance solar-driven CO2 reduction.