Anti-stacking synthesis of MXene-reduced graphene oxide sponges for aqueous zinc-ion hybrid supercapacitor with improved performance

Abstract

Two‑dimensional MXenes with an enormous active surface area are considered to be significant cathode materials for Zn‑ion hybrid supercapacitors. However, the nanosheets are easily self-restacked during the assembly into macroscopic porous electrodes, resulting in a significantly reduced effective surface area, hindering their applications in energy storage. Here, MXenes are subtly distributed on the surface of the sponge in a coral-like structure rather than participating in the assembly of the framework, which has suppressed the self-restacking of MXene effectively, improved the hydrophilicity of the sponge, and provided fast diffusion channels for electrolyte ions. Therefore, the MXene-TiC-reduced graphene oxide sponge exhibits excellent electrical conductivity, an enormous specific surface area with abundant accessible electroactive sites, and superior electrochemical performance. The resulting sponge demonstrates an outstanding specific capacity, up to 501 mAh g–1 at 0.2 A g–1, with excellent capacity retention (90%) after 3100 cycles as Zinc-ion hybrid supercapacitor cathodes. Furthermore, it exhibits an elegant gravimetric energy density of 486 mWh g–1 at 415 mW g–1, which has surpassed most leading MXene-based Zn-ion cathodes. This work provides a new synthetic idea for MXene-based macro-composites and paves a new avenue for designing next-generation flexible and portable porous electrodes with high gravimetric and rate performances.