High-performance Zn-ion hybrid supercapacitor based on 3D K+-intercalated Ti3C2TX hydrogel cathode

Aqueous zinc-ion hybrid supercapacitors (ZHSCs) exhibit great potential for energy storage and conversion devices, owing to their inherent safety and cost-effectiveness. Nevertheless, the structure of traditional porous carbon cathodes hinders the zinc-ion diffusion kinetics, rendering the energy densities of conventional ZHSCs uncompetitive and severely impeding their practical applications. 2D transition metal carbides/nitrides, known as MXenes, exhibit excellent conductivity and abundant surface functional groups, qualifying them as ideal candidates for constructing high-capacity cathodes in high-performance ZHSCs. This study presents the fabrication of a ZHSC utilizing 3D porous K⁺-intercalated Ti₃C₂T_X-reduced graphene oxide (K⁺-Ti₃C₂T_X-RGO) hydrogel as cathode, paired with a zinc foil as anode. Upon treatment with KOH solution, Ti₃C₂T_X undergoes K⁺ ion intercalation into its nanosheets, resulting in partial elimination of terminal -F groups and expansion of the MXene interlayer spacing. Subsequently, large-scale graphene oxide (GO) was employed as a conductive binder to interconnect the intercalated multilayer Ti₃C₂T_X, and a reducing agent was incorporated to facilitate self-assembly into a hydrogel. This approach augmented the accessibility of ions and facilitated their transport within the resultant structure. The ZHSC, fabricated with this composite cathode, synergistically integrates the supercapacitor’s high-power density and the battery’s high energy density. The results indicate that the ZHSC exhibited excellent electrochemical performance, featuring a high specific capacitance of 253.86 F g⁻¹ at 1 A g⁻¹ and an impressive energy density of 141.03 Wh kg⁻¹ at 999.99 W kg⁻¹. Notably, after 5000 charge-discharge cycles at 10 A g⁻¹, the ZHSC maintained a capacitance retention rate above 87.96%, highlighting its exceptional cycling stability.