title: A Nickel Dithiolate Water Reduction Catalyst Providing Ligand-Based Proton-Coupled Electron-Transfer Pathways.
abstract: A nickel pyrazinedithiolate ([Ni(dcpdt)2]2-; dcpdt=5,6-dicyanopyrazine-2,3-dithiolate), bearing a NiS4core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330-400 mV at pH 4-6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92-100 %. The electrochemical and DFT studies reveal that diprotonated one-electron-reduced species (i.e., [NiII(dcpdt)(dcpdtH2)]-or [NiII(dcpdtH)2]-) forms at pH<6.4 via ligand-based proton-coupled electron-transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low-valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Motooka 744, Nishi-ku, Fukuoka, 819-0395, Japan.|International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Koshiba
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Motooka 744, Nishi-ku, Fukuoka, 819-0395, Japan.|International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Japan.
authors.forename: Kosei
authors.initials: K
authors.lastname: Yamauchi
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Motooka 744, Nishi-ku, Fukuoka, 819-0395, Japan.|International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Japan.|Center for Molecular Systems (CMS), Kyushu University, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Sakai
keywords: artificial photosynthesis; hydrogen evolution; nickel complexes; proton-coupled electron transfer (PCET); pyrazine