V₂CT_x MXene as a Sacrificial Promoter for NiFe Catalyst for Anion Exchange Membrane Electrolyzers

Nickel-iron layered double hydroxides (NiFe-LDH) show excellent activity, their poor conductivity limits practical implementation in electrolysers. Previous reports have shown that combining nickel-iron layered double hydroxide (NiFe-LDH) materials with MXenes significantly increases the oxygen evolution reaction (OER) activity, however, the rationale behind this is not clear. Herein, we report operando X-ray absorption spectroscopy (XAS) of V₂CT_x MXene-enhanced NiFe-LDH catalysts, revealing important insights into MXene-hydroxide synergy. Operando X-ray absorption reveals a two-step vanadium transformation: V₂CT_x initially oxidizes during hydrothermal synthesis, acting as a reducing agent that promotes ordered Fe₂NiO₄ formation, then undergoes further oxidation under OER conditions, to form mixed-valence V³⁺/⁴⁺/⁵⁺ oxide species that establish transient electronic coupling with NiFe active sites. Finally, the NiFe@V₂CT_x composites were tested in an Anion Exchange Membrane (AEM) electrolyzer over 144 h of continuous operation at 500 and 1000 mA cm^-2, with NF25 achieving degradation rates as low as 0.76 mV h^-1 at 1000 mA cm^-2. Postmortem tests reveal that V₂CT_x undergoes progressive dissolution during operation, yet the structurally modified NiFe electrodes retain superior activity relative to the unmodified reference throughout the full test duration. These findings demonstrate that V₂CT_x functions beyond passive conductive support as an active electronic participant whose structural legacy sustains durable performance even after vanadium leaching.