Insights into Charge Transfer at the Cluster/semiconductor Interface for In-Depth Understanding the Role of Atomically Precise Silver Cluster

A cluster/semiconductor model is built for exploring the role of noble metal clusters in a photocatalytic system. The incorporation of an atomically precise nanocluster, e.g. Ag₄₄(SR)₃₀, onto a large band gap semiconductor such as TiO₂ allows to obtain a clear interface and thus simplify the system. The composite is employed for photocatalytic H₂ generation. It’s found that changing the light source from visible light to simulated sunlight leads to an enhancement by three orders of magnitude. The H₂ production rate reaches 7.4 mmol/h/g_catalyst which is five times higher than that of Ag nanoparticles modified TiO₂ and even comparable to that of the similar conditioned Pt nanoparticle modified TiO₂. Energy band alignment and transient absorption spectroscopy, together with other studies, reveal that the role of the metal clusters is different from both organometallic complexes and plasmonic-nanoparticles. A type-II heterojunction charge transfer route is achieved under UV-vis irradiation, in which the cluster serves as small band gap semiconductor. The type-II photosystem has a more efficient charge separation ability, which contributes significantly to the enhanced catalytic performance. This finding endows the clusters a broad platform as cocatalysts rather than merely photosensitizers in the applications of light energy conversion.