Ammonium Tetrathiomolybdate: A Versatile Catalyst for Hydrogen Evolution Reaction from Water under Ambient and Hostile Conditions

The lack of catalysts that can selectively reduce protons to produce hydrogen from water in the presence of oxygen and other conventional inhibitors of hydrogen evolution reaction (HER) has been a fundamental problem stalling the development of a practical hydrogen economy. Ammonium tetrathiomolybdate (ATM), a common laboratory reagent, spontaneously assembles on Au electrodes. Atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy data indicate formation of multiple layers of ATM which are stable over a wide pH range for days. These assemblies can produce hydrogen with very low onset potentials. It shows a turnover rate of 1.4 s(-1) and turnover number >5 X 10(4) in pH 7 at 180 mV overpotential. The pH dependence of the peak potential suggests that the generation of H-2 from water proceeds likely via a ligand based proton coupled electron transfer process which precludes inhibition by O-2. The ATM functionalized Au electrodes are found to efficiently catalyze HER in saline rich, CO saturated, and sulfide rich water sources with minimal inhibition of catalytic activity.