Extraordinary Structural Reconstruction of Nanolaminated Ta₂FeC MAX Phase for Enhanced Oxygen Evolution Performance

Renewable energy technologies, such as water splitting, heavily depend on the oxygen evolution reaction (OER). Nanolaminated ternary compounds, referred to as MAX phases, show great promise for creating efficient electrocatalysts for OER. However, their limited intrinsic oxidative resistance hinders the utilization of conductivity in M_n+1X_n layers, leading to reduced activity. In this study, a method is proposed to improve the poor inoxidizability of MAX phases by carefully adjusting the elemental composition between M_n+1X_n layers and single-atom-thick A layers. The resulting Ta₂FeC catalyst demonstrates superior performance compared to conventional Fe/C-based catalysts with a remarkable record-low overpotential of 247 mV (@10 mA cm^-2) and sustained activity for over 240 h. Notably, during OER processing, the single-atom-thick Fe layer undergoes self-reconstruction and enrichment from the interior of the Ta₂FeC MAX phase toward its surface, forming a Ta₂FeC@Ta₂C@FeOOH heterostructure. Through density functional theory (DFT) calculations, this study has found that the incorporation of Ta₂FeC@Ta₂C not only enhances the conductivity of FeOOH but also reduces the covalency of Fe─O bonds, thus alleviating the oxidation of Fe³⁺ and O^2-. This implies that the Ta₂FeC@Ta₂C@FeOOH heterostructure experiences less lattice oxygen loss during the OER process compared to pure FeOOH, leading to significantly improved stability. These results highlight promising avenues for further exploration of MAX phases by strategically engineering M- and A-site engineering through multi-metal substitution, to develop M₂AX@M₂X@AOOH-based catalysts for oxygen evolution.