Optimized agarose-based conductive hydrogel electrodes for capacitive deionization

Abstract

The development of advanced electrode materials is critical for improving the efficiency and durability of capacitive deionization (CDI) technologies for water desalination and separation processes. In this work, a novel conductive hydrogel based on agarose (Aga), tannic acid (TA), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was designed, optimized, and evaluated as a functional coating for CDI electrodes. The hydrogel formulation was systematically optimized by varying the TA and PEDOT:PSS contents, identifying an optimal composition containing 10 wt% TA and 20 wt% PEDOT:PSS. This formulation exhibited a favorable combination of mechanical robustness, high porosity (∼93%), well-distributed pore size, preserved swelling capacity, and enhanced electrochemical properties. Electrochemical characterization revealed improved cathodic stability and capacitive behavior, supporting enhanced ion storage and transport. When implemented in CDI cells, the hydrogel-coated electrodes demonstrated significantly enhanced salt adsorption capacity and higher charge efficiency compared to conventional activated carbon (AC) electrodes. Although the initial salt adsorption capacity was slightly lower than that of other soft-coated electrodes, the gel-based system showed progressive performance improvement and superior long-term cycling stability during aging tests. The enhanced hydration, facilitated ion transport, and sustained structural integrity contributed to improved operational efficiency and durability. Overall, the proposed Aga-TA-PEDOT:PSS hydrogel represents a promising electrode material for energy-efficient, stable, and scalable CDI systems, with potential applications in low-salinity and brackish water treatment.