Cobalt Phosphorous Trisulfide as a High-Performance Electrocatalyst for the Oxygen Evolution Reaction

Two-dimensional (2D) layered materials are currently one of the most explored materials for developing efficient and stable electrocatalysts in energy conversion applications. Some of the 2D metal phosphorous trichalcogenides (M 2 P 2 X 6 or MPX 3 in its simplified form) have been reported to be useful catalysts for water splitting, although results have been less promising for the sluggish oxygen evolution reaction (OER) due to insufficient activity or compromised stability. Herein, we report the OER catalysis of a series of M 2 P 2 X 6 (M 2+ = Mn, Fe, Co, Zn, Cd; X = S, Se). From the series of MPX 3, CoPS 3 yields the best results with an overpotential within the range of values usually obtained for IrO 2 or RuO 2 catalysts. The liquid-phase exfoliation of CoPS 3 even improves the OER activity due to abundant active edges of the downsized sheets, accompanied by the presence of surface oxides. The influence of the OER medium and underlying substrate electrode is studied, with the exfoliated CoPS 3 reaching the lowest overpotential at 234 mV at a current density of 10 mA/cm 2, also able to sustain high current densities, with an overpotential of 388 mV at a current density of 100 mA/cm 2, and excellent stability after multiple cycles or long-term operation. Quantum chemical models reveal that these observations are likely tied to moieties on CoPS 3 edges, which are responsible for low overpotentials through a two-site mechanism. The OER performance of exfoliated CoPS 3 reported herein yields competitive values compared to those reported for other Co-based and MPX 3 in the literature, thus holding substantial promise for use as an efficient material for the anodic water-splitting reaction.