title: Size- and shape-dependent activity of metal nanoparticles as hydrogen-evolution catalysts: mechanistic insights into photocatalytic hydrogen evolution.
abstract: The catalytic activity of Pt nanoparticles (PtNPs) with different sizes and shapes was investigated in a photocatalytic hydrogen-evolution system composed of the 9-mesityl-10-methylacridinium ion (Acr(+)-Mes: photocatalyst) and dihydronicotinamide adenine dinucleotide (NADH: electron donor), based on rates of hydrogen evolution and electron transfer from one-electron-reduced species of Acr(+)-Mes (Acr·-Mes) to PtNPs. Cubic PtNPs with a diameter of (6.3±0.6) nm exhibited the maximum catalytic activity. The observed hydrogen-evolution rate was virtually the same as the rate of electron transfer from Acr·-Mes to PtNPs. The rate constant of electron transfer (k(et)) increased linearly with increasing proton concentration. When H(+) was replaced by D(+), the inverse kinetic isotope effect was observed for the electron-transfer rate constant (k(et)(H)/k(et)(D)=0.47). The linear dependence of k(et) on proton concentration together with the observed inverse kinetic isotope effect suggests that proton-coupled electron transfer from Acr·-Mes to PtNPs to form the Pt-H bond is the rate-determining step for catalytic hydrogen evolution. When FeNPs were used instead of PtNPs, hydrogen evolution was also observed, although the hydrogen-evolution efficiency was significantly lower than that of PtNPs because of the much slower electron transfer from Acr·-Mes to FeNPs.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kotani
authors.forename: Ryo
authors.initials: R
authors.lastname: Hanazaki
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Yamada
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D000166:Acridines / Q000737:chemistry*; D002384:Catalysis; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D007554:Isotopes / Q000737:chemistry; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D015394:Molecular Structure; D009243:NAD / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*
chemical_list: C484398:9-mesityl-10-methylacridinium; D000166:Acridines; D007554:Isotopes; D009243:NAD; D010984:Platinum; D006859:Hydrogen; D007501:Iron