High-Entropy MXenes as Next-Generation Electrocatalysts for Efficient and Durable Hydrogen Evolution

In this study, we systematically investigated the role of configurational entropy and morphological control in enhancing the electrocatalytic performance of MXenes for the hydrogen evolution reaction (HER). We successfully synthesized a series of MAX phase precursors with increasing entropy: low-entropy (single-metal) Ti₂AlC, V₂AlC, Nb₂AlC; a medium-entropy solid solution (Ti₁/₃V₁/₃Nb₁/₃)₂AlC; and a high-entropy (Ti₁/₄V₁/₄Nb₁/₄Ta₁/₄)₂AlC. X-ray diffraction analysis confirmed the successful formation of layered hexagonal MAX phases and their transformation into MXenes, with characteristic shifts in the (002) reflection indicating interlayer expansion. Scanning and transmission electron microscopies reveal the evolution from dense, plate-like MAX grains to exfoliated, accordion-like multilayered Ti₁/₂V₁/₂Nb₁/₂Ta₁/₂CT_z MXene and sheets with few-layered morphologies, while X-ray photoelectron spectroscopy demonstrates Al removal and the presence of mixed oxidation states for Ti, V, Nb, and Ta. The electrochemical analysis of HER revealed a clear trend of improved activity with increasing entropy. Single-metal MXenes exhibited overpotentials (η@10 mA/cm²) of 231–207 mV and Tafel slopes of 163–155 mV/dec. The medium-entropy (Ti₁/₃V₁/₃Nb₁/₃)₂CT_z MXene demonstrated enhanced performance (η ≈ 140 mV, Tafel slope ≈ 134 mV/dec), which was further surpassed by the high-entropy (multilayered) M-(Ti₁/₄V₁/₄Nb₁/₄Ta₁/₄)₂CT_z MXene (η ≈ 97 mV, Tafel slope ≈ 115 mV/dec). Exfoliating the high-entropy MXene into few-layered F- (Ti₁/₄V₁/₄Nb₁/₄Ta₁/₄)₂CT_z (F-Mxene) nanosheets yielded a tremendous enhancement, achieving an exceptional overpotential of 67 mV and a Tafel slope of 69 mV/dec. Alongside this superior activity, the high-entropy F-MXenes demonstrated tremendous electrochemical stability under prolonged operation, maintaining their performance for more than 55 h of continuous use. This combination of record-low overpotential, favorable kinetics, and robust durability establishes these compositionally complex, few-layered MXenes as a promising next-generation catalyst platform, paving the way for their application in efficient and sustainable hydrogen production systems.