MXene/carbon based ultra-stable symmetric sodium-ion capacitors for glucose monitoring

Biomass-derived activated carbon and MXenes are promising candidates for high-performance electrochemical energy storage owing to their low cost and excellent charge-storage properties. Herein, we demonstrate a unified single-step molten-salt strategy to synthesize a composite of pumpkin seed-derived activated carbon and Ti₃C₂Tx MXene in a single pot for sodium-ion capacitor (SIC) applications. In this process, biomass is simultaneously carbonized and activated, while Ti₃AlC₂ MAX phase is etched to yield Ti₃C₂Tx MXene. The resulting composite (actC@Ti₃C₂) exhibits a highly porous hierarchical structure, enabling enhanced sodium storage capability. The SIC delivers high energy and power densities (43 kg-1 and 10,280 kg-1, respectively) along with excellent cycling stability, retaining ∼80% of its capacitance after 20,000 cycles with ∼99% Coulombic efficiency. A practical application of SIC was demonstrated by powering a glucometer, highlighting its potential in medical devices. Further, freshly assembled SICs powered a digital timer for over 2 h, while the long cycled (20k) SIC powered it for more than 1 h. The post-characterization of the electrodes suggested that only salt deposition on the active sites leads to the failure of the cells while the material structure is intact. This environmentally friendly, scalable, and cost-effective molten-salt approach provides a simple route for designing carbon-MXene (actC@Ti₃C₂) composites for next-generation electrochemical energy storage systems and sensing devices.