Wheel-shaped icosanuclear Cu-containing polyoxometalate catalyst: Mechanistic and stability studies on light-driven hydrogen generation

In this paper, we report the synthesis and characterization of a wheel-shaped icosanuclear-containing polyoxometalate (POM), K12Li13[Cu20Cl(OH)24(H2O)12(P8W48O184)]·22H2O (K12Li13-Cu20P8W48). The resulting cation-exchanged tetrabutylammonium salt of the polyoxoanion Cu20P8W48 (TBA-Cu20P8W48) exhibits high efficiency for visible-light-driven H2 production in the presence of an [Ir(ppy)2(dtbbpy)][PF6] photosensitizer and a triethanolamine electron donor. Under optimal conditions, the turnover number for H2 production reaches ∼2892 after 5 h of photocatalysis and thereafter continuously increases to ∼13400 in a long-term 120 h reaction, representing the best performance among all reported transition-metal-substituted POM catalysts. Mechanistic studies confirm the existence of reductive and oxidative quenching processes, of which the reductive quenching pathway is dominant. Various stability tests demonstrate that the TBA-Cu20P8W48 catalyst slowly dissociates Cu ions under turnover conditions; however, both the starting TBA-Cu20P8W48 and its molecular decomposition products are dominant active species for efficient and long-term H2 production.