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 Ni^II 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 d_z²-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.