A durable and pH-universal self-standing MoC-Mo₂C heterojunction electrode for efficient hydrogen evolution reaction

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC-Mo₂C catalytic electrode prepared via a one-step electro-carbiding approach using CO₂ as the feedstock. The outstanding HER performances of the MoC-Mo₂C electrode with low overpotentials at 500 mA cm^-2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 ^oC) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)-Mo₂C (101) heterojunctions that have a ΔG_H* value of -0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties.