Electrocatalytic hydrogen production from neutral water using an aqueous Ni(ii) pincer complex†
Abstract
Water is the exemplary source for sustainable H2 production and provides an ideal solvent for this electrocatalytic reaction. In neutral pH, aqueous saline solution, the NiII diminopyridiine precatalyst, [Ni(κ3-2,6-{PhNCMe}2(NC5H3))Br2] 1, electrocatalytically produced H2 with an onset voltage of −1.0 V (387 mV overpotential) versus Ag/AgCl. In anhydrous acetonitrile solution, trifluoroacetic acid supplied protons for H2 production with an overpotential of 555 mV. Computational analysis (DFT) provided insight into the identities of the catalysts and supported the non-innocent role of the ligand in the reduction chemistry. Mechanistic propositions for these observations, also supported computationally, suggested proton transfer to the dz2-based orbital of the reduced Ni(I) complex to generate a square planar Ni(II). A second proton transfer led to formation of a Ni(II) dihydrogen complex.