Molecular-Orbital-Based Verification of Water Photo-Splitting on Pt-Loaded TiO2: Effective Formation of HOOH and Reduced Platinum Cluster as Precursors of O2 and H2. (25th October 2017)

• Record Type: Journal Article
• Authors: Yanagida, Shozo; Yanagisawa, Susumu; Yamashita, Koichi; Jono, Ryota; Segawa, Hiroshi
• Is Part Of: ECS transactions. Volume 80:Number 10(2017)
• Page Start: 1091
• Page End: 1112
• Publication Date: 2017-10-25
• Subjects: Electrochemistry -- Periodicals; Electrochemistry; Periodicals; Electronic journals; Electronic journal; 541.37
• DOI: 10.1149/08010.1091ecst
• Languages: English
• ISSNs: 1938-5862

Abstract

Abstract : Sayama and Arakawa reported in 1997 that Pt-loaded nc-TiO2 catalyzes effective H2 O photo-splitting occurring in aqueous sodium carbonate solutions (pH8~11.5). Sayama and Arakawa's H2 O photo-splitting is now verified by density-functional theory-based molecular modeling (DFT/MM), where Yamashita-Jono's nc-TiO2 model of [HOTi9 O18 H], hydrated hydroxide anion model of [HO - &H2 O] and platinum triangular pillar model of [Pt6 ] are employed. At first, hydroxyl anion of HO - &H2 O is verified to undergo endothermic one-electron transfer oxidation, giving hydrogen peroxide of HOOH&(H2 O)2 via formation of hydroxyl radical of HO . &H2 O and its coupling. As for verification of electron-transfer reduction of Pt6 cluster for the H2 O photo-splitting to H2, the van der Waals complex of [Pt6 ] with nonpolar H2 O trimer model of [ts-(H2 O)3 ] is molecular-modeled, and highly exothermic electron transfer reactions verify the effective H2 formation via formation of hydrogen radical on [Pt6 ]. As the model of Pt-loaded nc-TiO2 catalyst, van der Waals and Coulomb interaction-based complex of [HOTi9 O18 H] with [Pt6 ] and [HO - &H2 O] is successfully molecular-modeled, and the molecular orbital energy structure rationalizes that the effective water-splitting catalysis should occur via effective electron transfer from HOMO of [HO - &H2 O] to LUMO of [Pt6 ] when the catalyst is photo-energized. DFT/MM also verifies successive oxidation of HOOH to 3 O2 and photo-regeneration of HOOH via radical anion of O2 .- that could be produced from 3 O2 under UV irradiance of Sayama and Arakawa's photocatalysis systems.