N-Doping Fe-C@Nb₂CT_x MXenes with High Stability and Strong Activity for Sodium-Ion Storage and Overall Water Splitting

The development of highly stable and strongly active electrode materials for sodium-ion batteries (SIBs) and overall water splitting (OWS) is critical in sustainable energy storage and conversion systems. Here, a new electrode material N-Fe-C@Nb₂CT_x is introduced, with a layered sandwich structure consisting of N-doping Fe-MOF derived-nanorods (Fe-C) and Nb₂CT_x MXenes. Specifically, Nb₂CT_x obtained by etching Nb₂AlC with HF acid is used as the main body to construct the layered sandwich structure with Fe-C as the filler. Benefiting from this structure, Fe-MOF grows in situ within Nb₂CT_x, which restrains MXenes aggregation and stacking and also alleviates the bulk effect of sodium-ion embedding/de-embedding, thus improving its stability. Again, the more exposed active sites from the layered sandwich structure and N-doping introduction ensure high reactivity as electrode materials. In addition, Fe-C nanorods strengthen the linkage between the Nb₂CT_x layers and N-doping enhances the ion/electron transport rate, thereby boosting the effective mass transfer and electrical conductivity. Density functional theory (DFT) calculations show that Fe-C and N-doping help increase the density of states (DOS) and material electrical conductivity. Meanwhile, the generated oxygen species (*OH and *O) in OER are captured by in situ FT-IR test. As a result, the N-Fe-C@Nb₂CT_x electrochemical test displays good electrochemical performance in SIBs and OWS.