Extending the Electrochemical Stability Window of Ti3C2Tz MXenes via Ta–Hf Co-Substitution for Durable Proton Exchange Membrane Fuel Cell Catalyst Supports

Abstract

MXenes are an emerging class of two-dimensional transition metal carbides with attractive electrical conductivity, surface chemistry tunability, and high surface area, making them promising candidates for electrocatalyst support materials in proton exchange membrane fuel cells. However, their practical use at positive electrochemical potentials is severely limited by rapid and irreversible oxidative degradation. Here, we demonstrate that introducing chemical disorder through oxyphilic metal co-substitution is an effective strategy to extend the electrochemical stability window of Ti3C2Tz MXenes. Hafnium- and tantalum–hafnium co-substituted MAX phases were synthesized and converted to corresponding MXenes, enabling systematic investigation of single and co-substitution effects. X-ray photoelectron spectroscopy reveals that Ta–Hf co-substitution suppresses titanium oxide formation and stabilizes the surface chemistry of the MXene. Electrochemical corrosion measurements show that the corrosion potential of optimized Ta–Hf co-substituted MXenes shifts positively by up to 94 mV relative to pristine Ti3C2Tz, accompanied by reduced anodic currents and delayed passivation. Operando element-resolved dissolution measurements further confirm suppressed metal leaching under anodic polarization. When employed as catalyst supports in proton exchange membrane fuel cells, Pt-loaded Ta–Hf co-substituted MXenes exhibit significantly improved durability during accelerated stress testing and anode reversal conditions compared to unsubstituted and singly substituted counterparts. These results establish oxyphilic metal co-substitution as a general materials design strategy for stabilizing MXenes under anodic conditions, enabling their application as durable catalyst supports in advanced fuel cell systems.