Atomically precise Au25(GSH)18 nanoclusters versus plasmonic Au nanocrystals: Evaluating charge impetus in solar water oxidation

Atomically precise metal nanoclusters (NCs) have been deemed as an emerging class of metal nanomaterials owing to fascinating size-dependent physicochemical properties, discrete energy band structure, and quantum confinement effect, which are distinct from conventional metal nanoparticles (NPs). Nevertheless, metal NCs suffer from photoinduced self-oxidative aggregation accompanied by in-situ transformation to metal NPs, markedly reducing the photosensitization of metal NCs. Herein, maneuvering the generic instability of metal NCs, we perform the charge transport impetus comparison between atomically precise metal NCs and plasmonic metal NPs counterpart obtained from in-situ self-transformation of metal NCs in photoelectrochemical (PEC) water splitting reaction. For conceptual demonstration, we proposed two quintessential heterostructures, which include TNTAs-Au25 heterostructure fabricated by electrostatically depositing glutathione (GSH)-protected Au25(GSH)18 NCs on the TiO2 nanotube arrays (TNTAs) substrate, and TNTAs-Au heterostructure constructed by triggering self-transformation of Au25(GSH)18 NCs to plasmonic Au NPs in TNTAs-Au25 via calcination. The results indicate that photoelectrons produced over Au25 NCs are superior to hot electrons of plasmonic Au NPs in stimulating the interracial charge transport toward solar water oxidation. This is mainly ascribed to the significantly accelerated carrier transport kinetics, prolonged carrier lifespan, and substantial photosensitization effect of Au25 NCs compared with plasmonic Au NPs, resulting in the considerably enhanced PEC water splitting performance of TNTAs-Au25 relative to plasmonic TNTAs-Au counterpart under visible light irradiation. Our work would provide important implications for rationally designing atomically precise metal NCs-based photosystems toward solar energy conversion.