Abstract
Appropriately designed catalysts help to minimise the energy required to convert the energy-poor feedstock H₂O into energy-rich molecular H₂. Herein, two families of pyridazine-based cryptates, mononuclear [MˡˡLi](BF₄)₂ and mixed metal dinuclear [MˡˡCuˡLi](BF₄)₃ (M = Fe, Co, Cu or Zn; Li is the Schiff base cryptand made by 2 : 3 condensation of tris(2-aminoethyl)amine and 3,6-diformylpyridazine), are investigated as potential electrocatalysts for the hydrogen evolution reaction (HER) in MeCN with acetic acid as the proton source. The synthesis and structures of a new mixed metal cryptate, [ZnˡˡCuˡLi](BF₄)₃, and the tetrafluoroborate analogue of the previously reported perchlorate salt of the mono-zinc cryptate, [ZnˡˡLi](BF₄)₂·0.5H₂O, are reported. Electrocatalytic HER testing showed that a deposit forms on the glassy carbon working electrode during electrolysis and it is the active species responsible for the very modest activity observed. The deposits formed by the heterobinuclear cryptates had higher activities (2.0 < TON₂ₕ < 3.5) than the deposits formed by the mononuclear cryptates (TON₂ₕ < 0.75). But unfortunately the control, using Cuˡ(MeCN)₄BF₄, had a similar TON₂ₕ (2.3) to those seen for the heterobinculear cryptates, which indicates that it is the deposit formed by the Cuˡ cation present in the heterobinuclear cryptates that is likely responsible for the observed, very modest, HER activity.