Electrocatalytic Application of 3d Transition Metal Complexes for Efficient Hydrogen Generation

Abstract

The production of hydrogen gas through green processes such as electrolysis is crucial in shifting away from fossil fuel derivatives, in order to enhance the viability of hydrogen as a sustainable energy alternative. This work investigates several complexes based primarily on 3d transition metals, in particular Mn, Fe, Ni, Cu, and additionally Mo for their electrocatalytic capabilities towards hydrogen evolution reactions (HER) with the electrolysis of water as the ideal proton source. A secondary proton source, acetic acid, was also investigated. In particular, the complexes explored were pyridine-based bidentate and tridentate Mn(I), Mo(0) and Mo(VI) species, macrocyclic quinquedentate complexes of Mn(II), Fe(III), Ni(II), Cu(II), and open-ended tetradentate complexes for Ni(II) and Cu(II). Four unreported crystal structures, using single crystal X-ray diffraction analysis, for Mn(II), Fe(III) and Ni(II) complexes were found. This research cumulated in the creation of a NiO/Ni(OH)₂ film electrodeposited onto a FTO glass electrode, with the source material being an open-ended tetradentate Ni(II) complex in 0.1 M KCl aqueous solution. This Ni-derived film provided good HER performance for the electrolysis of water in 0.1 M KCl solution, with results providing an average of 46.7 μmol of hydrogen as detected by GC TCD with the electrode held at -1.2 V (vs. Ag/AgCl) over 1 hr, with a Faradaic efficiency of ~96%.