Low-Cost Nanostructured Iron Sulfide Electrocatalysts for PEM Water Electrolysis

In the context of increased application of proton exchange membrane electrolyzers, the development of cheap and long-lived transition-metal hydrogen evolution reaction electrocatalysts is required to circumvent nonsustainable platinum-based electrocatalysts. Herein we report the synthesis and characterization of robust iron–sulfide nanoparticles from low-cost precursors (i.e., FeCl 3 and thiourea) using an easily scalable soft synthesis technique, which can achieve electrocatalysis. In the series of nanoparticles studied, we show that pyrite FeS 2 is the most active, in comparison with greigite Fe 3 S 4 and pyrrhotite Fe 9 S 10, in a three-electrode electrochemical cell, the electrocatalysis starting at an overpotential of ∼180 mV. These three materials exhibit a very stable behavior during the catalysis, with no activity decrease for at least 5 days. Fe x S y catalysts have been tested in a PEM electrolysis single cell, and pyrite FeS 2 allows achievement of a current density of 2 A/cm 2 at a voltage of 2.3 V.