Electron Transfer of Activated Carbon to Anode Excites and Regulates Desalination in Flow Electrode Capacitive Deionization

Abstract

The desalination performance of flow electrode capacitive deionization (FCDI) is determined by the ion adsorption on the powdered activated carbon (PAC) and the electron transfer between the current collector and PAC. However, a comprehensive understanding of rate-limiting steps is lacking, let alone to enhance FCDI desalination by regulating the PAC characteristics. This study showed that the electron transfer between PAC and the current collector on the anode side was the rate-limiting step of FCDI desalination. Compared with W900, the desalination performance of FCDI decreased by 95% when W1200 with weak electron transfer ability was used as a flow electrode. The PAC selected in this study transferred electrons directly through the conductive carbon matrix in FCDI and was mainly affected by graphitization. The desalination performance of FCDI was improved by 20 times when the graphitization degree of PAC increased from 0.69 to 1.03. The minimum energy required for electrons to escape from the PAC surface was reduced by the high degree of graphitization, from 4.27 to 3.52 eV, thus improving the electron transfer capacity of PAC on the anode side. This study provides a direction for the optimization of flow electrodes and further promotes the development of FCDI.

Asymmetric Fe2+/Fe3+-Mediated Flow-Electrode Capacitive Deionization for the Removal of Chloride Ions in Reclaimed Water

“…The increase in RE was due to the capacitive contribution of FCDI . That was, when chloride ions migrate into the anode solution and were then transiently stored on the AC, a double electric layer was formed on the surface of the AC . The contribution of the capacitive process was 27.48%.…”

Ion-Selective Metathesis Design of Flow-Electrode Capacitive Deionization for Energy-Saving and Anti-Scaling Softening of Brackish Water

“…This process requires a discharge protocol subsequent to the saturation of the electrode, which results in intermittent operation and reduced flow efficiency. , Alternatively, flow-electrode CDI (termed FCDI), which is one variant of CDI, can effectively overcome this limitation. Particularly, the operational mode known as the short-circuited closed-cycle of FCDI allows for the continuous regeneration of the flow electrodes through mixing oppositely charged flow electrodes external to the FCDI cell, which ensures a consecutive desalination process. − Following the mixture of the oppositely charged electrode, ions are released within the electrolyte of the flow electrodes, resulting in the formation of a concentrated brine solution. , Such a desorption process may cause gypsum to precipitate on the electrode and ion exchange membranes (IEMs) surfaces, affecting the stability of the FCDI system, particularly when treating brackish groundwater that contains naturally occurring Ca 2+ and SO 4 2– ions. , …”

“…15−17 Following the mixture of the oppositely charged electrode, ions are released within the electrolyte of the flow electrodes, resulting in the formation of a concentrated brine solution. 18,19 Such a desorption process may cause gypsum to precipitate on the electrode and ion exchange membranes (IEMs) surfaces, affecting the stability of the FCDI system, particularly when treating brackish groundwater that contains naturally occurring Ca 2+ and SO 4 2− ions. 20,21 The early CDI improvement agendas for brackish softening and antiscaling strategies were mainly focused on the exploration of novel materials and their integration into the CDI electrode.…”

Nanoarchitectonics of ultrafine molybdenum carbide nanocrystals into three-dimensional nitrogen-doped carbon framework for capacitive deionization

“…4–7 As is well known, electrode materials play indispensable roles in CDI, and the developments of advanced electrode materials have been recognized as a prospective strategy for improving desalination performance. 8 So far, various carbonaceous materials, such as activated carbon (AC), 9,10 carbon aerogels, 11,12 biomass-derived carbons, 13,14 carbon nanotubes, 15 and graphene, 16 have been synthesized and utilized as CDI electrodes. However, the salt adsorption capacity (SAC) of most traditional carbonaceous CDI electrodes is still unsatisfactory, 17,18 which might have originated from their deficient compositions or uncontrolled structures.…”