Effect of metal centers of complexes bearing bipyridine ligand for electrochemical- and photochemical-driven hydrogen evolution

In this work, two complexes with bipyridine ligand, [Co (bpy) 2 (SCN) 2 ] 1 and [Ni (bpy) 2 (SCN) 2 ] 2 have been prepared and well determined by single crystal X-crystallography, power X-ray diffraction (XRD), IR spectra, and so forth. Both exhibit good catalytic activity for electrochemical- and photochemical driven-hydrogen evolution. Complexes 1 and 2 can electro-catalyze H 2 evolution from a neutral buffer (pH 7.0) with a turnover frequency (TOF) of 699.6 and 1469 mol H 2 /mol catalyst/h at an overpotential (OP) of 837.6 mV, respectively. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid as a sacrificial electron donor, complexes 1 and 2 also can photo-catalyze H 2 evolution from water. Under an optimal condition, the turnover numbers (TONs) reach 10,600 (complex 1 ) and 15,180 (complex 2 ) mol of H 2 per mol of catalyst during 48-h irradiation, respectively. The average apparent quantum yields (AQYs) of complex 1 and complex 2 are 15.07% and 22.7%, respectively. Electrochemical and photochemical investigations show that the nickel complex has a higher activity for hydrogen evolution than that of the cobalt complex. These results can provide a new insight into design and manufacture of new H 2 -production catalyst. Highlights Reactions of bipyridine (bpy), KSCN and M II Cl 2 (M = Co and Ni) afford [Co (bpy) 2 (SCN) 2 ] 1 and [Ni (bpy) 2 (SCN) 2 ] 2 , respectively. Under an overpotential (OP) of 837.6 mV, 1 and 2 provide 699.6 and 1469 mol H 2 /mol catalyst/h from buffer solution, respectively. Complexes 1 and 2 also can photo-catalyze H 2 evolution with a turnover number (TON) of 10,544 and 15,160, respectively, respectively. Complex 2 exhibits a much higher catalytic efficiency for hydrogen production than 1 . The result is attributed to that nickel exhibits higher electronegativity than cobalt, amenable to binding to H + and hydrogen production, and a smaller bandgap in [Ni (bpy) 2 (SCN) 2 ] (1.104 eV) than in [Co (bpy) 2 (SCN) 2 ] (1.7443 eV).