Structure manipulation of CoFe catalysts via V2CTx MXene interactions for improved alkaline oxygen evolution

Abstract Two-dimensional MXenes have emerged as promising support materials for electrocatalysts due to their high electrical conductivity and tunable surface chemistry. This study introduces a hydrothermal synthesis approach using NH ₄ F as an additive to fabricate CoFe@V ₂ CT _x composites with systematically varied vanadium content. The NH ₄ F-mediated hydrothermal method redirected crystallization from large catalytically inert crystals toward interfacially nucleated CoFOH and FeOOH phases at the V ₂ CT _x surface, reaching maximum abundance in the catalytically optimal composition CFV17. CFV17 demonstrated a reduced overpotential of 304 mV at 10 mA cm ⁻² , a reduction in charge transfer resistance, and the lowest Tafel slope in the series. Operando X-ray absorption spectroscopy at the Co and Fe K-edges confirmed that CFV17 achieved cobalt and iron oxidation states exceeding their Co ³⁺ and Fe ³⁺ references at 150 mV lower potential compared to pure CoFe, mechanistically justifying the enhanced OER activity. Post-stability ICP-OES analysis confirmed that V ₂ CT _x stabilizes the CoFe active phase against dissolution. This work establishes V–O–Fe interfacial coordination as the central mechanistic principle leading to OER enhancement in CoFe@V ₂ CT _x composites and demonstrates that the NH ₄ F hydrothermal synthesis route enables the compositional and interfacial control required to maximize this effect.