Improving the electrochemical desalination performance of chloride-doped polyaniline activated carbon electrode by tuning the synthesis method

Abstract

Activated carbon obtained from chloride-doped polyaniline (PAC/Cl) is an attractive material for brackish water desalination using capacitive deionization (CDI), due to its easy synthesis, low cost, and fast electrosorption kinetics. However, its low content of surface oxygen groups (SOGs) suppresses the salt adsorption capacity (SAC), despite high specific surface area. In this work, different strategies to improve the SAC and boost the kinetics of PAC/Cl electrodes were investigated by modifying the synthesis procedure. Firstly, the use of Pluronic F127 (PLR) as a template (CTAK electrode) allowed modification of the structure and textural properties of the carbonized and activated samples, increasing the SOG content by 26 % (from 4.2 to 5.3 at.%), compared to the electrode prepared in the absence of PLR (CTAK*). Consequently, the electrode hydrophobicity was reduced by 2.1-fold (from 87.4 to 40.9°) and the desalination performance was enhanced, especially using an asymmetric electrode configuration (SAC enhancement from 11.4 to 21.0 mg g−1). Despite the slower kinetics observed using CTAK, compared to CTAK*, when the SAC and electrosorption/desorption kinetics were considered together, CTAK outperformed CTAK* by ∼ 2.0-fold (from 932 to 1560 mg g−1 day−1), in both symmetric and asymmetric configurations. As a second approach, the use of PLR combined with hydrothermal carbonization, despite leading to a 3D hierarchical framework, hindered the access to the pores, negatively impacting the process kinetics. The results showed that the use of PLR-modified PAC/Cl is a simple and effective strategy for obtaining low-cost activated carbons with distinct surface chemistry that can improve desalination performance.