A nickel complex, an efficient cocatalyst for both electrochemical and photochemical driven hydrogen production from water

Abstract Inspired by that nickel complexes can act as molecular catalysts for hydrogen generation from organic acid or water, we choose a nickel(II) complex, [Bz-4-MePy] 2 [Ni II (i-mnt) 2 ] 1 (i-mnt 2−  = iso-maleonitriledithiolate, Bz-4-MePy +  = 1-benzyl-4′-methylpyridinium ion) as a potential catalyst. Electro- and photochemical investigations show that this nickel complex can act as both an electrocatalyst and a photocatalyst for H 2 generation from water via an unstable nickel hydride intermediate. A homogeneous electrocatalytic system containing complex 1 can afford 577.4 mol of H 2 per mole of catalyst per hour (mol H 2 /mol catalyst/h) from neutral water at an overpotential (OP) of 837.6 mV. Together with CdS nanorod (CdS NR) as a photosensitizer, and ascorbic acid (H 2 A) as a sacrificial electron donor in a pH 3.5 aqueous solution, under photoirradiation with blue light (λ max  = 469 nm), complex 1 also can provide hydrogen with a turnover number (TON) of 55340 mol of H 2 per mole of catalyst during first 60 h irradiation. The highest apparent quantum yield (AQY) is ∼26.8% at 420 nm.