2D transition metal carbides/nitrides (MXenes) have excellent physicalchemical properties, which makes them promising for electrochemical energy storage devices. However, because of their inherent self-stacking and narrow interlayer spacing, it is rarely used in multivalent ion energy storage systems. In this study, fatty diamines and aromatic diamines with different molecular sizes are inserted between MXene interlayers as pillars through a one-step amination process to inhibit the self-stacking and obtain different expanded interlayer spacings with improved antioxidant stability. X-ray diffraction results show that interlayer spacing of MXene increases from 1.23 to 1.40 nm. The p-phenylenediamine-intercalated MXene (PDA-MXene) exhibits better matching interlayer spacing (1.38 nm) and pore structure for improved electrolyte-accessible surface area, enhanced charge-transport properties, and promoted Zn 2+ ions storage. Therefore, zinc-ion hybrid supercapacitor (ZHSC) using PDA-MXene as cathode exhibits higher specific capacitance (124.4 F g −1 at 0.2 A g −1 ) in 2 m ZnSO 4 electrolyte together with outstanding cycling stability (85% capacity retention after 10 000 cycles at 1 A g −1 ). This study provides a route for precise control of MXene interlayer spacing by small organic molecules, which can be used to observe efficient charge storage in MXene-based electrochemical energy storage devices by optimizing interlayer spacing.

Zinc ion capacitors (ZICs) hold great promise in large-scale energy storage by inheriting the superiorities of zinc ion batteries and supercapacitors. However, the mismatch of kinetics and capacity between a Zn anode and a capacitive-type cathode is still the Achilles' heel of this technology. Herein, porous carbons are fabricated by using tetra-alkali metal pyromellitic acid salts as precursors through a carbonization/ self-activation procedure for enhancing zinc ion storage. The optimized rubidium-activated porous carbon (RbPC) is verified to hold immense surface area, suitable porosity structure, massive lattice defects, and luxuriant oxygen functional groups. These structural and compositional merits endow RbPC with the promoted zinc ion storage capability and more matchable kinetics and capacity with a Zn anode. Consequently, RbPC-based ZIC delivers a high specific energy of 178.2 W h kg −1 and a peak power density of 72.3 kW kg −1 . A systematic ex situ characterization analysis coupled with in situ electrochemical quartz crystal microbalance tests reveal that the preeminent zinc ion storage properties are ascribed to the synergistic effect of the dual-ion adsorption and reversible chemical adsorption of RbPC. This work provides an efficient strategy to the rational design and construction of high-performance electrodes for ZICs and furthers the fundamental understanding of their charge storage mechanisms or extends the understanding toward other electrochemical energy storage devices.

Zinc‐ion capacitors (ZICs) are promising technology for large‐scale energy storage by integrating the attributes of supercapacitors and zinc‐ion batteries. Unfortunately, the insufficient Zn2+‐storage active sites of carbonaceous cathode materials and the mismatch of pore sizes with charge carriers lead to unsatisfactory Zn2+ storage capability. Herein, new insights for boosting Zn2+ storage capability of activated nitrogen‐doped hierarchical porous carbon materials (ANHPC‐x) are reported by effectively eliminating the micropore confinement effect and synchronously elevating the utilization of active sites. Therefore, the best‐performed ANHPC‐2 delivers impressive electrochemical properties for ZICs in terms of excellent capacity (199.1 mAh g−1), energy density (155.2 Wh kg−1), and durability (65 000 cycles). Systematic ex situ characterizations together with in situ electrochemical quartz crystal microbalance and Raman spectra measurements reveal that the remarkable electrochemical performance is assigned to the synergism of the Zn2+, H+, and SO42− co‐adsorption mechanism and reversible chemical adsorption. Furthermore, the ANHPC‐2‐based quasi‐solid‐state ZIC demonstrates excellent electrochemical capability with an ultralong lifespan of up to 100 000 cycles. This work not only provides a promising strategy to improve the Zn2+ storage capability of carbonaceous materials but also sheds lights on charge‐storage mechanism and advanced electrode materials’ design for ZICs toward practical applications.

No abstract