Extraordinary Structural Reconstruction of Nanolaminated Ta 2 FeC 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+1 X 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+1 X n layers and single-atom-thick A layers. The resulting Ta 2 FeC 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 Ta 2 FeC MAX phase toward its surface, forming a Ta 2 FeC@Ta 2 C@FeOOH heterostructure. Through density functional theory (DFT) calculations, this study has found that the incorporation of Ta 2 FeC@Ta 2 C not only enhances the conductivity of FeOOH but also reduces the covalency of Fe─O bonds, thus alleviating the oxidation of Fe 3+ and O 2- . This implies that the Ta 2 FeC@Ta 2 C@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 M 2 AX@M 2 X@AOOH-based catalysts for oxygen evolution.