Sub-Nanometer Cobalt on Tungsten Titanium Carbide MXene (W2TiC2Tx): An Electrocatalyst for Highly Efficient and Stable Alkaline Hydrogen Evolution at Industrial-Scale Current Density.

Developing non-precious electrocatalysts that simultaneously deliver high activity, long-term durability, and industrial operability remains the critical challenge for the alkaline hydrogen evolution reaction (HER). Herein, a structurally well-defined two-dimensional metal carbide MXene, tungsten titanium carbide (W2TiC2Tx), is synthesized for the first time via the W2TiAlC2 MAX-phase precursor. Cobalt loading combined with rational modulation of local atomic configurations and metal-support interactions (MSI) enables the construction of a highly active and robust Co/W2TiC2 HER catalyst. The optimized Co/W2TiC2-700 exhibits small overpotentials of 63 and 191 mV at 10 and 100 mA cm- 2, and outstanding long-term durability of over 1000 h stable hydrogen production at 4000 mA cm- 2. In a flow-cell MEA electrolyzer, Co/W2TiC2 delivers near-unity hydrogen Faradaic efficiency across a wide current range (50-400 mA cm- 2) while requiring significantly lower cell voltages than commercial Pt/C. Quasi-in-situ XPS, XANES, and EXAFS analyses reveal that thermal modulation induces the transformation of Co from isolated atoms and large nanoparticles into uniform sub-nanometer particles anchored on the outer tungsten layers. DFT calculations identify Co-W interfacial sites as the primary active centers. This work highlights the critical role of rational design and utilization of MSI in MXene-supported catalysts for electrochemical water splitting.