Synchronously manipulating Zn²⁺ transfer and hydrogen/oxygen evolution kinetics in MXene host electrodes toward symmetric Zn-ions micro-supercapacitor with enhanced areal energy density

Sluggish divalent charges (e.g., Zn²⁺) diffusion within MXene host electrodes due to the larger sizes and stronger coulomb interactions compared to those of dominant univalent charges is an essential issue in developing MXene-based microsupercapacitors (MSCs) of higher theoretical energy densities. Herein, MXene/bacterial cellulose fiber (BCF) hybrid films with effectively expanded interlayer spacing between re-stacked few-layered MXene sheets via homogeneous intercalation of BCF nanospacer were designed and prepared. The electrochemical testing and molecular dynamics simulation demonstrated the consequently widened ions-transport-channels between few-layered MXene sheets can effectively reduce the diffusion barrier of Zn²⁺ within the MXene/BCF host electrodes compared to pure MXene film electrodes without BCF nanospacer. Further in-situ Raman and ex-situ XPS spectroscopy characterizations suggest: the consequently accelerated Zn²⁺ diffusion involved adsorption/desorption featured charge storage, and followed electrochemical reaction of Zn²⁺ with oxygen terminal groups on the MXene flakes induced additional pseudocapacitance within the MXene/BCF host electrodes simultaneously contribute to the acquired superior areal capacitance of the fabricated symmetrical aqueous Zn-ions MSCs (ZMSCs) based on the MXene/BCF host electrodes and Zn(CF₃SO₃)₂/polyacrylamide hydrogel electrolyte. Meanwhile, combined with doubled voltage window (1.2 V) benefiting from the cocurrently suppressed kinetics of hydrogen/oxygen evolution within the MXene/BCF host electrodes, a tremendously increased areal energy density (34.0 μWh cm⁻²) in comparison with that employing conventional H₂SO₄/polyacrylamide hydrogel electrolyte (0.6 V/8.6 μWh cm⁻²) is finally realized. The work demonstrates a simple and effective strategy to synchronously boost bivalent Zn²⁺ diffusion and depress hydrogen/oxygen evolution within MXene host electrodes toward symmetric ZMSCs of high areal energy density.