Two-Dimensional, Few-Layer Phosphochalcogenide, FePS₃: A New Catalyst for Electrochemical Hydrogen Evolution over Wide pH Range

A layered MPS 3 -type compound, FePS 3, is introduced as an electrocatalyst for hydrogen evolution reaction (HER). The non-noble metal-based FePS 3 is a semiconductor that could be solvent exfoliated into few-layer, two-dimensional (2D) nanosheets. The 2D thin sheets exhibit very good catalytic activity and stability toward HER over a wide pH range of acidic, alkaline, phosphate buffer, and 3.5 wt % aqueous NaCl solutions. The Tafel slope and exchange current density in acidic medium are determined to be ∼(45–50) mV dec –1 and 1 ± 0.2 × 10 –3 A cm –2, respectively. The stability of the catalyst is found to be very good. Density functional theory calculations reveal P and S as favorable hydrogen adsorption sites. This material opens up a new class of ternary, layered semiconductors for various electrocatalytic studies and might also become important from a device physics point of view.