| The fresh water crisis, which was previously predicted to be one of humans’main challenges in the following decades, has already swept over 80% of the global population because of the unexpected climate change and explosive population growth. In light of these emergency threats, novel water purification technologies are urgent for people to obtain pure and secure fresh water from sea or brackish water. As a robust, energy-efficient, and cost-effective alternative for desalination, capacitive deionization (CDI) has garnered greater attention than other conventional approaches in recent years. As a typical electrostatic field guided adsorption process, charged ions in the CDI process are expected to aggregate and form an electrical double layer (EDL) on the electrode interface. Consequently, porous carbon electrode materials, which commonly possess high specific surface areas, controllable pore size distribution, and acceptable electrical conductivity, are usually more favorable in CDI because of their excellent EDL performance. Among all, monolithic carbon electrode materials, which are more convenient to be assembled and easier to achieve higher CDI performance, commonly have more advantages and values in further CDI applications.This study was aimed at finding out the core connection between CDI performance and the structure of electrode materials, and then designing and synthesizing novel monolithic carbon electrode materials with high electrosorption capacity and charge efficiency for CDI. The electrosorption mechanism of CDI was studied by employing several commercial activated carbon materials. The intraparticle diffusion step was found to be the rate-determining step. The specific surface area and mesopore rate of electrode materials were verified to be the key points for CDI performance, which can be concluded that hierarchical porous structure with enough mesopores and abundant micropores are mostly beneficial for CDI. Highly mesoporous activated carbon, such as samples named ACk2 in this study, showed excellent regeneration ability and exhibited significantly high performance in recovery of trace metal ions, which can be a promising commercial application of CDI in the future. Based on the theory study above, electrospinning technique was used to prepare monolithic carbon nanofibers (CNFs) with controllable pore size distribution, and a better CDI module called flow-through module was specially designed for monolithic CNFs electrodes. The CDI electrosorption capacity and charge efficiency achieved an improvement of 1.87 times and 1.51 times compared to classical flow-by CDI module with CNFs as electrodes, respectively. Furthermore, highly mesoporous PCNF electrodes, prepared by PVP-template method, achieved better energy-effective CDI performance. In order to improve the charge efficiency of as-prepared monolithic CNFs electrode, SG-CNFs electrodes with better wettability, electrochemical performance and cation-selectvity was further prepared according to the combination of electrospun monolithic CNFs electrodes and sulfonated graphene by dip-coating process. The as-prepared SG-CNFs electrodes achieved great improvements of 22% in terms of both CDI electrosorption capacity and charge efficiency. Dramatically, the C-SC asymmetrical CDI electrode pair with SG-CNFs as cathode and CNFs as anode exhibited better CDI performance with 9.54 mg·g-1 in electrosorption capacity and 42.5% in charge efficiency, which were 1.9 times compared to classical symmetrical CDI electrode pair with CNFs as electrodes and exhibited multi-mode operability and long-term operation stability as some advantages of typical membrane capacitive deionization (MCDI). Thereby, a novel high-performance MCDI strategy by employing cation-selective electrode in asymmetrical electrode pair as the replacement of commercial cation-elective membrane in MCDI was designed and put forward. |
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