Flow electrode capacitive deionization with iron-based redox electrolyte

Desalination, vol. 578, pp. 117313

Abstract

Flow electrode capacitive deionization (FCDI) employs carbon-based materials for electrochemical separation. Redox additives like vanadium, ferricyanide, and organic molecules have boosted desalination rates in FCDI. However, these additives must be low-cost, have chemical stability in electrolytes, and have low toxicity. We investigate two iron-based redox couples, iron chloride, and iron citrate, for their cost-effectiveness and reduced health risks. We incorporate them with activated carbon (AC) in flow electrodes, resulting in a significant enhancement of the salt removal rate, with iron chloride increasing it by 100 % and iron citrate by 23 % compared to standard AC slurries. In our system, the AC exhibits a salt removal rate of 7.8μmolcm−2min−1, while the iron chloride system reaches 15.6μmolcm−2min−1. Iron citrate flow electrodes achieve a desalination rate of 9.6μmolcm−2min−1, maintaining a pH suitable for potable water. We observe that iron chloride concentration in the flow electrode influences iron crossover and pH in the water streams, leading to acidity. Conversely, the iron citrate-based slurry maintains minimal iron crossover and a neutral pH. This study highlights iron-based redox additives as promising for FCDI slurries and the need for tailored flow electrode composition based on specific ion removal requirements.

Authors 5

1. Nelson Henrique Jardim Freire Aachen DWI-Leibniz-Institute for Interactive Materials e.V

   Universidade Federal de Minas Gerais · DWI – Leibniz Institute for Interactive Materials

   Affiliation as printed

   DWI - Leibniz Institute for Interactive Materials e.V., Forckenbeckstraß e 50, 52074 Aachen, Germany

   Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

2. Christian J. Linnartz Aachen DWI-Leibniz-Institute for Interactive Materials e.V

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI - Leibniz Institute for Interactive Materials e.V., Forckenbeckstraß e 50, 52074 Aachen, Germany

   RWTH Aachen University, Aachener Verfahrenstechnik-Chemical Process Engineering, Forckenbeckstraß e 51, 52074 Aachen, Germany

3. Luciano A. Montoro

   Universidade Federal de Minas Gerais

   Affiliation as printed

   Department of Chemistry, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

4. Virgínia S.T. Ciminelli

   Universidade Federal de Minas Gerais

   Affiliation as printed

   Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

   Instituto Acqua, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG 31270-901, Brazil

5. Matthias Weßling corresponding Aachen DWI-Leibniz-Institute for Interactive Materials e.V

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI - Leibniz Institute for Interactive Materials e.V., Forckenbeckstraß e 50, 52074 Aachen, Germany

   RWTH Aachen University, Aachener Verfahrenstechnik-Chemical Process Engineering, Forckenbeckstraß e 51, 52074 Aachen, Germany