Charge and Potential Balancing for Optimized Capacitive Deionization Using Lignin‐Derived, Low‐Cost Activated Carbon Electrodes

Abstract

Lignin-derived carbon is introduced as a promising electrode material for water desalination by using capacitive deionization (CDI). Lignin is a low-cost precursor that is obtained from the cellulose and ethanol industries, and we used carbonization and subsequent KOH activation to obtain highly porous carbon. CDI cells with a pair of lignin-derived carbon electrodes presented an initially high salt adsorption capacity but rapidly lost their beneficial desalination performance. To capitalize on the high porosity of lignin-derived carbon and to stabilize the CDI performance, we then used asymmetric electrode configurations. By using electrodes of the same material but with different thicknesses, the desalination performance was stabilized through reduction of the potential at the positive electrode. To enhance the desalination capacity further, we used cell configurations with different materials for the positive and negative electrodes. The best performance was achieved by a cell with lignin-derived carbon as a negative electrode and commercial activated carbon as a positive electrode. Thereby, a maximum desalination capacity of 18.5 mg g was obtained with charge efficiency over 80 % and excellent performance retention over 100 cycles. The improvements were related to the difference in the potential of zero charge between the electrodes. Our work shows that an asymmetric cell configuration is a powerful tool to adapt otherwise inappropriate CDI electrode materials.

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…[182,183] Yue et al [107] prepared carbon@Na 4 Ti 9 O 20 (C@NTO) core-shell nanotube composites as electrodes for CDI application. As displayed in Figure 11c, two distinct peaks (−0.22 and −0.38 V) confirm the reaction of NTO with Na + in solution, which correspond to the Ti 4+ /Ti 3+ redox in accordance with the following equation Na 4 Ti 9 O 20 + 9Na + + 9e − ↔ Na 13 Ti 9 O 20 (13) Thus, the C@NTO-based HCDI cell provided a high desalination capacity of 80.56 mg g −1 at 1.4 V as shown in Figure 11d. Another case in point is a reduced graphene oxide@Na 4 Ti 9 O 20 composite, [106] which was synthesized through a hydrothermal process and also delivered a good desalination capacity of 42 mg g −1 in a HCDI system.…”

“…Carbon materials have been widely employed as electrode for CDI cells, such as activated carbon (AC), [13] carbon nanotubes, [14] graphene, [15] mesoporous carbon, [16] carbon frameworks, [17] and carbon aerogel, [18] which have obvious merits, such as abundant resources, easy to produce, good electrical conductivity, and tunable porous structure. Meanwhile, the CDI consisting of carbon electrodes has made great development in cell design, [19][20][21] pore structure optimization, [22] and modification of Donnan model for exploring the ion electrosorption process, [23,24] which leads several effective improvements in desalination performance.…”

Modification of Cation-Exchange Membranes with Polyelectrolyte Multilayers to Tune Ion Selectivity in Capacitive Deionization

“…The η values observed during the electrosorption process were comparable with the literature values. 77 , 78 …”

Activated Carbon Derived from Phoenix dactylifera (Palm Tree) and Decorated with MnO2 Nanoparticles for Enhanced Hybrid Capacitive Deionization Electrodes

“…In recent years, the capacitive deionization (CDI) process has been proposed as a promising technology for the removal of ions from water in view of its convenient desalination efficiency, exceptionally low energy consumption and environmental compatibility . Though the concept of CDI was introduced in the 1960s, the extent of its technological implementation has been far from practical in the absence of energy‐ and cost‐efficient electrode materials that offer sufficient ion‐storage capacity, fast ion‐transport channels and desirable sustainability . The conventional CDI process is based on the selective electrosorption of cations and anions at the electrical double layer (EDL) formed within the pores of oppositely‐charged electrodes .…”