Size- and Shape-Dependent Activity of Metal Nanoparticles as Hydrogen-Evolution Catalysts: Mechanistic Insights into Photocatalytic Hydrogen Evolution

Authors

  • Dr. Hiroaki Kotani,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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  • Ryo Hanazaki,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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  • Dr. Kei Ohkubo,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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  • Dr. Yusuke Yamada,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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  • Prof. Dr. Shunichi Fukuzumi

    Corresponding author
    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
    2. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
    • Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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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 (ket) 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 (ket(H)/ket(D)=0.47). The linear dependence of ket 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[BOND]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.

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