Hydrogen serves as a promising alternative carbon-free fuel and is an essential building block for industrial and agricultural processes. Currently, 95% of industrial H2 derives from fossil-fuel cracking, which is environmentally unsustainable. As such, the development of hydrogen evolution reactions (HER) from water/acid for H2 production and hydrogen oxidation reaction (HOR) catalyst for H2 consumption are significant. The utility of H2 as an energy storage/recovery agent has been exploited since the earliest forms of life through reactions at the metal-sulfur cores of Marcetta’s favorite metalloenzymes, hydrogenases (H2ases). While H2ases and most synthetic HER catalyst are proposed to operate via metal-hydride intermediates, we have developed two generations of ligand-centered HER catalysts employing ligand-centered reactions learned from Marcetta. The first generation catalyst, Re(PS)3 (PS = diphenylphosphinebenzenethiolato) relies on the redox non-innocence of the thiolate ligands, which direct electron/proton activity onto the ligand framework initiating a movement of charge through the cis-sulfur atoms, culminating in H-atom release and H2 evolution via radical coupling. The second generation catalysts employ a redox-active, conjugated bis(thiosemicarbazone) ligand with the first row transition metal Cu and the non-transition metal Zn. The Cu catalyst evolves H2 via radical coupling associated with homolytic N-H bond cleavage, while the Zn catalyst invokes hydride-proton coupling associated with heterolytic N-H bond cleavage. Reaction mechanisms are supported by cyclic voltammetry including digital simulations and kinetic isotope effect studies and density functional theory computation.

Hydrogen evolution without metal-hydrides: Ligand-centered HER catalysts with transition metals and non-transition metals

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.