The design of pseudocapacitive electrodes that exhibit high-rate and high volumetric capacitances is a big challenge, since it requires subtle modulation of ion-intercalation structures that are able to achieve high electrochemical activity, fast ion transport, and facilitated electron transfer, simultaneously. Herein, controllable and selective etching of B atoms from B-doped Ti 3 AlC 2 precursors is reported, which generates boron-vacancy doped MXene (B-V-MXene) nanosheets with finely-regulated, ion-intercalation structures. Electrochemical studies and density-functional-theory calculations demonstrate that Ti around vacancies possess higher surface-redox activity with protons than those on pristine MXenes for the improvement of capacitances. In addition, interlayer spacing can be optimized on B-V-MXenes in promoting proton intercalation. More importantly, the dopant B atoms can increase the electron density on Ti, facilitating the adsorption of the intercalated protons; and further, B 2p-Ti 3d hybridized band sits closer to the Fermi energy than that of C 2p bands, which bridges the energy gap for electron transfer in the pseudo-capacitive reaction. With synergy of all these effects, the novel B-V-MXene compact electrodes can deliver the previously unmatched high volumetric capacitances of 807 F cm −3 at 1,000 mV s −1 and 1,815 F cm −3 at 5 mV s −1 , with excellent cycle stability over 10,000 cycles.
Fiber-shaped supercapacitors (FSCs) serve as optimal energy storage components in wearable platforms. However, traditional fiber materials suffer from poor interfacial cross-linking, disordered microstructures, insufficient active sites, and low electrical conductivity. To overcome these challenges, this research develops Zn-MoO₃/Ti₃C₂Tₓ hybrid fibers via wet-spinning technology employing glacial acetic acid as a coagulation bath, with MoO₃ quantum dots intercalated into Ti₃C₂Tₓ interlayers and Ti₃C₂Tₓ nanosheets cross-linked by Zn 2+ . The resulting hybrid fibers feature expanded interlayer spacing, a large ion-accessible surface area, abundant porous channels, exceptional electrical conductivity, and excellent mechanical properties, delivering an exceptional volumetric capacitance of 2078.2 F cm −3 at 2 A cm −3 with 75.0 % capacitance retention at 20 A cm −3 . Furthermore, the constructed FSCs achieve a substantial energy density of 55.6 mWh cm −3 at a power density of 400 mW cm −3 , with 94.7 % capacitance retention after 5000 cycles, and successfully power an electronic timer, demonstrating their potential for wearable applications.
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