N, S co-doped composite carbon aerogel derived from konjac glucomannan/fucoidan/nitrogen-enriched carbon nanotubes as electrode materials for capacitive deionization

Abstract

Natural polysaccharides derived carbon aerogels possess multiple advantages, including diverse sources, inherent heteroatom doping, abundant functional groups, and unique primitive biological channels, rendering them suitable as electrode materials in capacitive deionization (CDI). In this work, we construct a novel N, S co-doped composite carbon aerogel (FuKNCA-y) derived from konjac glucomannan (KGM)/fucoidan (Fu)/nitrogen-enriched carbon nanotubes (N-CNTs) via directional freezing method. Among them, KGM serves as both the carbon source and structural matrix, Fu acts as the S source and a secondary component, while N-CNTs provide rich N source and optimize the pore structure, significantly boosting the overall electrical conductivity. The synthesized FuKNCA-y exhibits a large specific surface area, a hierarchical porous structure, excellent mechanical properties, and N, S co-doping. These characteristics collectively improve its hydrophilicity, increase active sites, modulate the electronic structure, and ultimately lead to the improved desalination performance. Specifically, the optimal FuKNCA-6 electrode achieves a salt adsorption capacity of 32.8 mg g⁻¹ and an average salt adsorption rate of 4.02 mg g⁻¹ min⁻¹ (500 mg L⁻¹ NaCl solution and 1.2 V), with superior cycling stability. Density functional theory calculations reveal the underlying enhancement mechanism of N, S co-doping and its significant synergistic effect on CDI performance. Therefore, this work provides a new method for synthesizing advanced heteroatom-doped carbon aerogels derived from natural polysaccharides for high-performance CDI electrodes.