Turning etching by-products into active sites: <i>In situ</i> construction of MoB/ZnS heterostructures for high-rate sodium-ion capacitors

High-performance sodium-ion capacitor anodes require the simultaneous achievement of rapid kinetics and structural robustness. However, conventional MBene synthesis involves the wasteful removal of metallic etching by-products and hazardous acid washing, often compromising material quality. Herein, a “turning-waste-into-wealth” strategy is proposed to construct MBene/transition metal sulfide heterostructures. By directly sulfurizing the intermediate Zn retained from Lewis-acid molten-salt etching, MoBTx/ZnS heterostructures are synthesized via a solvent-free, in situ process. This approach effectively prevents MBene oxidation and converts the “waste” Zn into active ZnS nanoparticles firmly anchored on the conductive MoBTx framework. The MoBTx backbone ensures high-speed electron transport and stress relaxation, while ZnS introduces abundant active sites. Consequently, the anode exhibits exceptional rate capability (47% capacity retention from 0.05 to 1 A g−1) and superior durability (100% retention over 300 cycles). This work provides a scalable, low-damage route for upgrading MBenes into advanced heterostructures for high-rate energy storage.