BiOCl atomic layers with electrons enriched active sites exposed for efficient photocatalytic CO2 overall splitting

Photocatalytic CO₂ splitting into value-added chemicals using solar energy is a promising strategy to address the greenhouse effect and energy challenges. However, existing photocatalysts often suffer from poor activity due to limited exposure of active sites and rapid recombination of photogenerated charge carriers. Now, researchers from Xi’an Jiaotong University and Tamkang University, led by Professor Shaohua Shen, have developed a novel BiOCl atomic layer structure (BOCNSs-i) that significantly enhances photocatalytic CO₂ splitting performance. Their findings, published in Nano-Micro Letters, demonstrate a remarkable improvement in CO production rates and offer new insights into the design of high-performance photocatalysts.

Why BiOCl Atomic Layers Matter

• Enhanced Photocatalytic Performance: The exfoliated BiOCl atomic layers (BOCNSs-i) exhibit a significantly improved photocatalytic activity for CO₂ overall splitting, producing CO and O₂ at a stoichiometric ratio of 2:1. The CO evolution rate reaches 134.8 µmol g^-1 h^-1 under simulated solar light (1.7 suns) and 13.3 mmol g^-1 h^-1 under concentrated solar irradiation (34 suns).
• Efficient Charge Carrier Transfer: The reduced thickness of BOCNSs-i enhances charge carrier separation and transfer by shortening the diffusion distance and increasing the built-in electric field intensity.
• Active Site Exposure: The introduction of oxygen vacancies (VO) enriches the electron density at Bi sites, facilitating the activation of CO₂ molecules and lowering the energy barrier for the rate-determining step (RDS) of the reaction.

Innovative Design and Mechanisms

• Preparation of BOCNSs-i: Hydrothermally synthesized BiOCl nanosheets (BOCNSs) were exfoliated into ultrathin nanosheets (BOCNSs-w) and atomic layers (BOCNSs-i) via ultrasonication in water and isopropanol, respectively. The exfoliation process significantly reduced the thickness of the nanosheets, enhancing their specific surface area and exposure of active sites.
• Charge Carrier Dynamics: Steady-state photoluminescence (PL) and time-resolved transient PL decay spectra revealed that the average lifetime of photogenerated carriers was prolonged in BOCNSs-i compared to bulk BOCNSs, indicating more efficient charge separation.
• In Situ Spectroscopic Investigations: In situ XPS and DRIFTS experiments demonstrated that electrons enriched Bi sites in BOCNSs-i effectively activated CO₂ molecules, reducing the energy barrier of the RDS. The presence of H₂O vapor during the reaction facilitated the exchange of oxygen atoms between H₂O and CO₂, further enhancing the photocatalytic performance.

Future Outlook

• Scalability and Practical Applications: The scalable synthesis of BOCNSs-i and their excellent stability under concentrated light irradiation highlight their potential for practical applications in solar-driven CO₂ conversion.
• Mechanistic Insights: This study provides a comprehensive understanding of the molecular and atomic fundamentals of photocatalytic CO₂ splitting, offering valuable insights for the rational design of high-performance photocatalysts.
• Further Research: Future work may focus on exploring other layered materials and optimizing reaction conditions to further enhance photocatalytic efficiency and selectivity.

Stay tuned for more exciting developments from Professor Shaohua Shen and the team at Xi’an Jiaotong University as they continue to push the boundaries of photocatalysis for sustainable energy solutions!