Synthesis and characterization of metal-diaminobipyridine complexes as low-cost co-catalysts for photo-sensitized hydrogen evolution

• Published in: Inorganica Chimica Acta Vol. 482; pp. 821 - 829
• Main Authors: Chand Vagvala, Tarun, Ooyabe, Takashi, Sakai, Munetoshi, Funasako, Yusuke, Inokuchi, Makoto, Kurashige, Wataru, Negishi, Yuichi, Kalousek, Vit, Ikeue, Keita
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-10-2018; Elsevier Science Ltd
• Subjects: Catalysis; Catalysts; Chemical synthesis; Co-catalyst; Coordination compounds; Copper; Crystal structure; Diaminobipyridine; H2 evolution; Hydrogen; Hydrogen evolution; Low cost; Metal complex; Nickel; Protonation; Single crystals; Metal complex; Diaminobipyridine; H2 evolution; Co-catalyst; Crystal structure
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2018.07.022

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•Novel 4,4′-diamino-2,2′-bipyridyl complexes of Co(III), Ni(II), and Cu(II) were synthesized.•The activities of above complexes for photocatalytic hydrogen evolution were probed.•The Cu(II) complex showed much higher active co-catalyst effect than Co(III) and Ni(II) complexes.•The H2 evolution mechanism and redox potentials of metal complexes were elucidated.•The Cu complexes enhanced the activity of a benchmark K2PtCl4 system.
We synthesized novel 4,4′-diamino-2,2′-bipyridine (dabpy) complexes of Cu(II), Co(III), and Ni(II), and determined their molecular structures by single-crystal XRD analysis. As a result, we found that [Cu(dabpy)2]2+ had a four-coordinated Cu center and distorted square-planar geometry, while the Co(III) and Ni(II) complexes contained six-coordinated metal centers and exhibited an octahedral geometry. The prepared complexes were investigated as co-catalysts for H2 evolution from aqueous media in the presence of erythrosin B as a photosensitizer. Notably, the Cu(II) complex demonstrated a much higher co-catalyst activity than the corresponding Co(III) and Ni(II) species. Additionally, the H2 evolution mechanism and the redox potentials of the metal dabpy complexes were elucidated using electrochemical studies, and it was found that the reduction of protons to H2 was accompanied by a Cu(II)/Cu(I) redox reaction. In addition, it was suggested that the high co-catalyst activity of the Cu(II) complex was due to the low protonation-induced overpotential compared to those of Co(III) and Ni(II). Furthermore, the photo-sensitized H2 evolution activity of the metal complex/K2PtCl4 mixed systems were shown to exceed that of the K2PtCl4-only control system. The Cu(II) complex was found to be low-cost and effective co-catalyst for homogeneous H2 evolution system.