Ternary Pentlandites as Hydrogen Evolution Catalysts in Alkaline Media

Metal sulfides are promising alternatives to noble metal electrocatalysts for water-based hydrogen evolution. Pentlandites, notably, exhibit high activity in acidic environments. To explore their potential in alkaline conditions, pentlandite electrodes are tested in both conventional three-electrode setups and scaled up to a 12.6 cm² membrane electrode assembly (MEA). Optimized pentlandites with a stochiometry of M9S8r containing Fe, Ni, and Co, show reduced overpotentials for hydrogen evolution with higher Fe and Ni contents. However, a minimum Co content of three equivalents is necessary for peak hydrogen evolution reaction activity with -0.40 V versus reversible hydrogen electrode at -300 mA cm². Stability assessments via X-ray photoelectron and Raman spectroscopy reveal minor surface changes for Fe and Ni species but significant leaching of cobalt from CO4.5S8 surfaces postelectrolysis. Selected pentlandite catalysts are integrated into MEAs, with Fe4CO3Ni2S8 achieving 1 A cm ² at 2.2 V with minimal potential decay of 50 μV h1 alongside a La0.8Sr0.2CoO3 anode. These findings underscore the suitability of pentlandite catalysts for water splitting at industrial scales under alkaline conditions.