Sequential K+ and Cs+ Intercalation into Ti3C2TX-Reduced Graphene Oxide Hydrogel for Enhanced Performance of Zinc-Ion...

Preintercalation engineering is an effective strategy for regulating MXene interlayer structures. However, the competitive behavior among different cations is rarely reported. Herein, we elucidate the competitive intercalation mechanism of Cs+ in K+-preintercalated Ti3C2TX and its impact on the performance of zinc-ion hybrid supercapacitors (ZHSCs). K+ preintercalation expands the interlayer galleries and lowers the diffusion barrier for the subsequent Cs+ insertion. Because of its larger ionic radius and stronger electrostatic interaction, Cs+ competitively replaces most of the preintercalated K+, resulting in a further enlarged and stabilized interlayer spacing. When the resultant K+/Cs+-Ti3C2TX is integrated into a 3D conductive hydrogel, restacking is effectively suppressed, and ion/electron transport is facilitated. For a ZHSC constructed with a zinc plate and an electrode based on reduced graphene oxide-supported K+/Cs+-Ti3C2TX hydrogel, a high specific capacitance of 255 F g-1 is achieved at 1 A g-1 with excellent cycling stability. Results from this work reveal the intrinsic significance of competitive cation intercalation in enhancing the performance of MXenes in energy-storage devices.