Rapid Inversion of Surface Charges in Heteroatom‐Doped Porous Carbon: A Route to Robust Electrochemical Desalination

Abstract

Given that a considerably large population suffers from shortage of water, there are numerous on‐going efforts to turn seawater into freshwater, and electrochemical desalination processes—particularly capacitive deionization (CDI)—have gained significant attention due to their high energy efficiency and reliable performance. Meanwhile, carbonaceous electrode materials, which are most commonly used in CDI systems, have poor long‐term stability due to unfavorable interactions with oxygen in saline water. Herein, rapid and vigorous inversion of surface charges in heteroatom‐doped carbon electrodes, which leads to a robust operation of CDI with high desalination capacity, is reported for the first time. By carbonization of coffee wastes, nitrogen‐ and sulfur‐codoped activated carbon with hierarchical micro/mesopores are prepared in an environmentally‐friendly manner, and this carbon results in a significantly higher inverted capacity than that of various activated carbon counterparts in long‐term CDI operations, without any sign of drop in performance. Investigations on the changes in physicochemical properties of the electrodes during the inversion disclose the favorable roles of nitrogen and sulfur dopants, which can be summarized as enlarging the difference between the surface charges of the two electrodes by chemical interactions with oxygen in the anode and carbon in the cathode.

Graphene–carbon 2D heterostructures with hierarchically-porous P,N-doped layered architecture for capacitive deionization

“…[11][12][13] Accordingly, there has been substantial effort focused on the synthesis of porous carbon materials having appropriate characteristics to achieve optimal CDI performance. [14][15][16][17][18] Unfortunately, however, most porous carbon materials obtained by simple processing routes exhibit poor salt adsorption capacity (SAC) because of their limited functionality, which leads to a sparsity of charged groups at their surfaces, narrow pore size distribution and low electrical conductivity, 19 although they can have very large SSAs and highly microporous structures. The application-oriented design of nanostructured porous carbon is therefore critical for the practical scale-up CDI applications.…”

Reborn Three‐Dimensional Graphene with Ultrahigh Volumetric Desalination Capacity

“…In addition, conductive agents and binders that have a negative effect on porosity and CDI capacity [15] are usually used to solve the problems of poor adhesion and low conductivity during electrode preparation. [16][17][18] Designing new materials and constructing specific 3D microstructures of electrodes are of great significance for CDI technology.…”

Carbon‐Based Capacitive Deionization Electrodes: Development Techniques and its Influence on Electrode Properties

“…Kang et al . used a coffee‐derived activated carbon (CDAC) containing N and S functionalities [117] . They tested its performance during long‐term cycling (100 cycles) and compared its performance with three other commercial activated carbons (MSP20X, S51HF, and YS2).…”