Identifying Reactive Sites & Surface Traps in Solar Fuel production

Gathering information on the atomic nature of reactive sites and trap states is key to fine tuning catalysis and suppressing deleterious surface voltage losses in photoelectrochemical technologies for direct solar-to-fuel production. In a new “hot paper” published in Angewandte Chemie, Liu et al. combine spectroelectrochemical and computational methods to investigate a model photocathode from the promising chalcopyrite family: CuIn_0.3Ga_0.7S₂ (CIGS). Interestingly, it was found that voltage losses are linked to traps induced by surface Ga and In vacancies, whereas operando Raman spectroscopy revealed that catalysis occurred at Ga, In, and S sites (not Cu). This result establishes an important bridge between chalcopyrite's performance and its surface's chemistry, where avoiding formation of Ga and In vacancies is crucial for achieving high activity, and is a step towards inexpensive solar-driven H₂ production.