Interface functional groups protected by confinement effect for flexible supercapacitor and capacitive deionization

Biomass, as one of the most promising carbon precursors, mainly focuses on its special original nanostructures at present. However, the biological diversity and uncontrollability are not conducive to its application in high-precision fields. In this work, the biomass, separated into soluble substances, are applied to the multi-cavity nanospheres (NC-PPD) and ultra-thin nanosheets (BC-PPD) modified by functional group ( p -phenylenediamine) interface, thus without depending on their original morphology. On account of similar carbon components from the same precursor, the single-factor function relation, the confinement effect on surface functional groups and its influence law in flexible supercapacitor (SC) and capacitive deionization applications, are studied in detail. Overall, the interface modification optimizes the hydrophilicity of the material, increases its actual reachable specific surface area and pseudocapacitance contribution. Most importantly, the confinement effect enhances the stability of surface functional groups, and reduces the material damage from capacitive reaction (retains 80.2% initial capacitance after 10 4  cycles). Moreover, the multi-chamber structure strengthens the material stability and alleviates the adverse effects of material breakage. For SC, the NC-PPD//NC-PPD device provides large energy density of 8.8 Wh kg −1 and maximum power density of 2.5 k W kg −1. For CDI, salt adsorption capacity can be up to 33.2 mg g −1.