Unveiling the quantum capacitance of Zr3C2T2 (T = O, F) for high-performance Zn-ion hybrid supercapacitors

The design and development of advanced energy storage systems with both long cycling life and high-power densities has long been a research hotspot. Zinc-ion hybrid supercapacitors (ZHSCs) are regarded as emerging and highly promising candidates, combining the advantages of both supercapacitors and zinc-ion batteries (ZIBs). The widespread use of zinc-ion aqueous systems in ZIBs is due to the abundance, high specific capacity (>800 mAh/g), and low toxicity of zinc. In this work, we demonstrate that oxygen- and fluorine-terminated zirconium-based MXenes (Zr 3 C 2 O 2 /Zr 3 C 2 F 2 ) can act as reversible zinc-ion hosts for ZHSCs. Based on the density functional theory (DFT) calculations, Zr 3 C 2 O 2 presents exceptional electrochemical performance, featuring a maximum quantum capacitance C Q of 1519 μF/cm 2 in aqueous systems, and Zr 3 C 2 F 2 a value of 1510 μF/cm 2 . In ionic/organic systems, the maximum C Q of Zr 3 C 2 F 2 dominates. The findings suggest that Zr 3 C 2 O 2 and Zr 3 C 2 F 2 are suitable for both aqueous and ionic/organic electrolytes of hybrid supercapacitors. Similarly, both MXenes showed superior theoretical specific capacity and a suitable open-circuit voltage range, which are characteristics of advanced electrodes. These insights provide a theoretical foundation that may inform the future development of MXene-based ZHSCs with enhanced power density and cycling stability. • Zr 3 C 2 T 2 demonstrates higher quantum capacitance and charge density values. • Zr 3 C 2 T 2 exhibits substantial values of theoretical specific capacity. • The average open-circuit voltage displayed by Zr 3 C 2 O 2 (Zr 3 C 2 F 2 ) is 0.33 (0.24) V. • Enhanced charge transfer is observed in Zn-adsorbed Zr 3 C 2 O 2 systems.