Eutectoid-structured WC/W2C heterostructures: A new platform for long-term alkaline hydrogen evolution reaction at low overpotentials

One of the major challenges encountered in hydrogen evolution reaction (HER) electrocatalysis is the development of highly-efficient catalysts suitable for use in alkaline media. Tungsten carbide-based materials have long been advocated as potential alternatives to platinum (Pt) for HER process due to their "Pt-like" electronic structures. However, they exhibit significant HER activity mostly in acid but not in alkali. Herein, we report a robust synthetic method for directly growing a unique eutectoid-structured WC/W2C heterostructure (ES-WC/W2C) that can serve as a highly active electrocatalyst for alkaline HER via calcination of a special two-dimensional organic-inorganic tungsten precursor. This novel ES-WC/W2C catalyst exhibits high alkaline HER activity with an ultra-low onset-potential of 17 mV and a low overpotential of 75 mV at 10 mA/cm2 (ɳ10). It yields an ultra-high exchange current density of 0.58 mA/cm2, an enhancement of nearly 14- and 12-fold in comparison with the phase-pure WC and W2C, respectively. Even when normalized to the electrochemically active surface area (ECSA), the normalized current density (J0, normalized) is still significantly higher than the J0, normalized for phase-pure WC and W2C, demonstrating the substantial improvement of intrinsic activity by constructing such heterostructures. Moreover, it also exhibits an exceptionally stability in alkaline solutions, showing no evidence of significant degradation over 480 h (>20 days) of H2 production, far exceeding the stability of other tungsten carbide-based electrocatalysts. To the best of our knowledge, this is the first time such a eutectoid-structured material has been reported to efficiently catalyze the HER in alkaline solution.