Abstract
Hydrogen (H2) is considered the most promising clean energy source to replace conventional fossil fuels. Despite the exceptional catalytic activity of Pt-group metals, the high cost and relatively low durability of these noble metal-based catalysts remain key bottlenecks for sustainable hydrogen production at the industrial scale. In this report, we synthesized a new type of MXene, tungsten titanium carbide (W2TiC2). By loading cobalt (Co) onto the surface of W2TiC2, we developed a highly effective and stable catalyst for alkaline hydrogen evolution reaction (HER). The optimized catalyst exhibited a small overpotential of 62.58 mV at 10 mA/cm2 and a low Tafel slope of 44.34 mV/dec. At high current density of 100 mA/cm2 and 1000 mA/cm2, the low overpotentials of 191.18 mV and 407.72 mV were achieved, significantly outperforming the commercial Pt/C electrode. Under both current ranges, our catalyst exhibited excellent stability of 500 h at 10 mA/cm2 and for 100 h at 1000 mA/cm2 without any obvious degradation. In flow cell tests, by pairing with Ni foam, our catalyst also required much lower cell voltage than commercial Ni foam||Pt/C and maintained ~ 100% H2 faradaic efficiency over the 15h continuous tests from 100 to 400 mA/cm2. X-ray absorption near edge structure (XANES) demonstrated a temperature induced redistribution of Co on MXenes from single sites and large nanoparticles (NPs) to uniform small NPs. Density functional theory (DFT) calculations, combined with X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS), revealed that the HER activity was sensitive to the coordination environment of Co on W2TiC2, and the Co-W interface is the likely HER active site . This work sheds light on structure design and utilization of metal-support interaction (MSI) in MXene-supported metal catalysts for the efficient electrochemical water splitting at industrial scale.