Physicochemical double protection enables stable MXene for high-rate performance hybrid supercapacitors

MXene, with metallic conductivity, strong hydrophilicity, and rich chemistries, has been widely used as electrode material for energy storage. However, the notorious issues of aggregation and oxidation for MXene significantly inhibit its electrochemical performance and further wide application. Herein, a physicochemical double protection strategy is proposed to stabilize MXene in the hydrothermal process effectively. Polyvinylpyrrolidone (PVP), with the structure of a long chain and abundant O/N function groups, provides physical protection against agglomeration (steric effect) and chemical protection against oxidation (electron transfer) at the same time, contributing to the synthesis of MXene-based hybrids with high conductivity and fully exposed active sites. As proof of the concept, 2D MXene/Co₉S₈ nanohybrids with a scaly surface are fabricated and present impressive performance, especially rate performance for hybrid supercapacitor (HSC) with MoS₂ as the counter electrode. The HSC demonstrates a high energy density of 111 Wh kg⁻¹ at 845 W kg⁻¹ and an excellent rate performance of 61 Wh kg⁻¹ at 16.9 kW kg⁻¹.