Phase-engineering terraced structure of edge-rich α-Mo₂C for efficient hydrogen evolution reaction

Molybdenum carbide (Mo₂C) nanomaterials have become potential candidates for hydrogen evolution reaction (HER) electrocatalysts. However, the electrocatalytic performance of powdery Mo₂C is restricted because of the insufficient active sites and structural integrity of the organic binders. In this study, α-Mo₂C nanosheets with a terraced structure and numerous edges were directly synthesized on a Cu/Mo substrate as a self-supported electrode and used as an electrocatalyst for HER without binder and transfer processes. The terraced α-Mo₂C nanosheets exposed numerous active sites with mixed polymorphs (1T and 1H phases) and Bernal (AB) stacking. They showed long-term stability and satisfactory HER activity, with overpotentials of 226, 324, and 294 mV vs. RHE (at a current density of 10 mA·cm⁻²) and Tafel slopes of 74, 104, and 63 mV/dec in 1.0 M KOH, 1.0 M PBS, and 0.5 M H₂SO₄, respectively. Density functional theory calculations revealed that the 1T-1H interface and Bernal stacking at the terraced α-Mo₂C enhance the electrocatalytic performance compared to 2D α-Mo₂C.