Unraveling Dynamic Interplay on Defective Indium Sites During CO2 Photoreduction

Why It Matters

The work demonstrates how precise defect engineering can overcome kinetic bottlenecks in photocatalytic CO₂ reduction, offering a pathway to more efficient solar fuel production.

Key Takeaways

• S vacancies enrich electrons on neighboring indium sites
• Operando XPS and IR reveal CO₂ adsorption dynamics
• In‑CO inversion hinders CO desorption on defective In₂S₃
• O substitution suppresses CO inversion, boosting activity fivefold

Pulse Analysis

Defect engineering has emerged as a cornerstone of modern heterogeneous catalysis, yet the exact role of individual vacancies in shaping reaction pathways often remains elusive. In the case of indium sulfide (In₂S₃), a semiconductor prized for its visible‑light response, creating sulfur vacancies not only modifies the electronic structure but also generates localized indium sites with heightened electron density. These electron‑rich sites act as strong anchors for CO₂ molecules, facilitating their activation and subsequent conversion under illumination. By leveraging operando X‑ray photoelectron spectroscopy alongside infrared spectroscopy, the study captures real‑time changes at the atomic level, providing a rare glimpse into the dynamic surface chemistry that drives photocatalysis.

The spectroscopic investigations uncovered a sequential transformation of adsorbed CO₂ into *COOH and then *CO intermediates, mirroring classic CO₂ reduction mechanisms. However, a novel and detrimental phenomenon was identified: an "upside‑down" inversion of the *CO binding configuration from In‑*CO to In‑*OC. This inversion creates a kinetic trap, severely limiting CO desorption and thus throttling overall catalytic turnover. The discovery underscores how subtle alterations in surface geometry can have outsized effects on product release, a factor often overlooked in catalyst design.

To address the inversion bottleneck, the researchers introduced oxygen atoms to replace residual sulfur at the defect sites, effectively tuning the electronic environment of the indium centers. This O‑substitution stabilizes the conventional In‑*CO binding mode, preventing the inversion and enabling a five‑fold increase in CO evolution rates compared with pristine In₂S₃. The findings not only provide a concrete strategy for boosting photocatalytic efficiency but also illustrate the broader potential of operando techniques to rationally engineer defect landscapes. As the push for sustainable solar fuels intensifies, such insights will be pivotal in guiding the next generation of high‑performance, defect‑tailored catalysts.