Gill-Inspired Biomimetic Engineering Enables 100 000-Cycle Stable Potassium Storage of MXene

MXene materials suffer from critical challenges including poor air stability, sheet restacking, sluggish K storage kinetics, and structural collapse during cycling. Inspired by biological interface functions, this work constructs an organic-inorganic biomimetic MXene-4-MVA composite through chemical coupling between 4-methylvaleric acid (4-MVA) and the functionalized MXene surface. The 4-MVA functions as a molecular pillar to expand interlayer spacing, expose active sites, and buffer volume deformation while forming a protective layer that inhibits MXene oxidation. Simultaneously, the interfacial charge redistribution induced by 4-MVA modification generates an interfacial dipole effect, which regulates charge transfer behavior and K⁺ adsorption kinetics. Experimental tests and density functional theory (DFT) calculations reveal that the organic modification regulates interfacial K adsorption behavior and ion transport characteristics. Consequently, the obtained MXene-4-MVA exhibits an excellent specific capacitance of 59.0 F g^-1 at 0.5 A g^-1. The assembled aqueous symmetric MXene-4-MVA // MXene-4-MVA supercapacitor achieves an ultrahigh capacitance retention of 92.1% after 100 000 cycles at 5 A g^-1, exceeding the cycling stability of most state-of-the-art supercapacitors. This study providing new insights for the design and preparation of highly stable MXene-based energy storage electrodes.