Redox-electrodes for selective electrochemical separations

Su, Xiao; Hatton, T. Alan

doi:10.1016/j.cis.2016.09.001

Cited by 139 publications

(100 citation statements)

References 151 publications

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“…[ 10 ] To this end, electroactive polymers and inorganic materials have been used for energy storage applications in supercapacitors and batteries, [ 11 ] as well as electrochemically‐mediated aqueous separations. [ 12 ] Electrochemically‐mediated separation processes are especially attractive since electrochemical degradation techniques can often be energetically expensive, and can create unwanted by‐products. [ 6 ] Of particular note is that electrochemical separation processes can be designed for molecular targeting in selectively removing certain species where methods such as distillation and chromatography may be inefficient, [ 1 ] a concept that has previously been used in the development of ion‐selective electrochemical sensors.…”

Section: Introductionmentioning

confidence: 99%

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

Tan

Hatton

2020

Adv Funct Materials

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Electrochemically mediated redox-active processes are gaining momentum as a promising liquid-phase separation technology. Compared to conventional systems, they offer potential benefits, such as smaller energy footprints, nondestructive operation, reversibility, and tunability for specific analyte removal, with clear applications to societal and industrial challenges like water treatment and chemical synthesis. An asymmetric Faradaic cell heterogeneously functionalized with a metallopolymer at the anode and a hexacyanoferrate material at the cathode is presented for the first time. The redox-active species' iron centers enhance the electrosorption of heavy metal oxyanions with up to 98% removal in the ppb range, and offer tunable operating windows as low as ≈0.1 V at ≈1 A m −2 . By avoiding water splitting, the hexacyanoferrate cathode imparts additional advantages, namely a fourfold reduction in adsorption energy requirements, full suppression of solution pH increase, and the ability to capture redox-active catalytic anions such as polyoxometalates without altering their bulk oxidation state. This hybrid framework of a polymeric ferrocene anode and crystalline hexacyanoferrate cathode allows for simultaneous and synergistic uptake of anions and cations, respectively, creating a new asymmetric scheme for water-based separations, with foreseeable future extension to fields such as ion-sensing, energy storage, and electrocatalysis.

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Section: Introductionmentioning

confidence: 99%

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

Tan

Hatton

2020

Adv Funct Materials

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confidence: 99%

“…Recent work has shown redox‐active/Faradaic materials as an attractive platform for selective water contaminant removal . Redox‐active metallopolymers have demonstrated remarkable uptake of anions with significant selectivity, both of organic anions and heavy metal oxyanions 8b,9. At the same time, asymmetric electrochemical systems have traditionally been proposed in energy‐storage applications to enhance capacitance and electrochemical properties .…”

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“…Tandem Faradaic systems have been successfully used previously as a medium to minimize side‐reactions and increase current efficiency 8c,11. In this study, an asymmetric redox‐active design is proposed, in which a working electrode is functionalized with a poly(vinyl)ferrocene (PVF), and the counter‐electrode with poly‐TEMPO‐methacrylate (PTMA), a polymer containing redox‐active nitroxide radical moieties (see Figure a).…”

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Asymmetric Redox‐Polymer Interfaces for Electrochemical Reactive Separations: Synergistic Capture and Conversion of Arsenic

et al. 2019

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in water as anionic arsenate (As(V)) or arsenite (As(III)), with the latter being acutely toxic and difficult to remove. [3] Commonly employed techniques to remove arsenic are coagulation-flocculation or chemical adsorption, both which require significant chemical input, and extensive pretreatment steps for As(III) to As(V) conversion. [3c] Thus, novel removal technologies that integrate removal and conversion of arsenic are critical for sustainable environmental management.The development of advanced materials for water purification, selective contaminant removal, and improved energy efficiency is critical to tackling water-energy nexus challenges, including through the design of more effective membranes and field-assisted adsorbents. [4] Electrochemical methods for water treatment such as capacitive deionization (CDI) have garnered increased attention as a desalination technology, and also as a heavy metal removal platform, due to their efficiency and low environmental footprint compared to typical methods. [5] Electrosorption systems benefit from inherent modularity and scalability, which opens the door to point of source remediation systems. Electrochemical conversion of As(III) to As(V) on carbon electrode has been investigated previously for CDI-based arsenic remediation. [5l,6] However, low arsenic selectivity in the presence of competing ions has limited the total uptake capacity of carbon-based CDI, [5c,h-l] as most arsenic contaminated water sources are composed of 10 to 1000-fold excess salts. [7] Thus, the design of molecularly selective functional adsorbents is necessary to address these materials chemistry limitations.Recent work has shown redox-active/Faradaic materials as an attractive platform for selective water contaminant removal. [8] Redox-active metallopolymers have demonstrated remarkable uptake of anions with significant selectivity, both of organic anions and heavy metal oxyanions. [8b,9] At the same time, asymmetric electrochemical systems have traditionally been proposed in energy-storage applications to enhance capacitance and electrochemical properties. [10] Here, we leverage this electrochemical design for the first time to integrate both the separation and the reactions step electrochemically at functionalized electrodes. We seek to combine two redox-active polymer Advanced redox-polymer materials offer a powerful platform for integrating electroseparations and electrocatalysis, especially for water purification and environmental remediation applications. The selective capture and remediation of trivalent arsenic (As(III)) is a central challenge for water purification due to its high toxicity and difficulty to remove at ultra-dilute concentrations. Current methods present low ion selectivity, and require multistep processes to transform arsenic to the less harmful As(V) state. The tandem selective capture and conversion of As(III) to As(V) is achieved using an asymmetric design of two redox-active polymers, poly(vinyl)ferrocene (PVF) and poly-TEMPO-methacrylate (PTMA). D...

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“…During charging, there is an input of electrical energy, which can partially be recovered during discharge [140]. Many CDI architectures are possible including the use of flowing electrodes [5,77,79], chemically modified electrodes [151], redox-active materials [91,152], and the addition of ion-exchange membranes [37,38,71]. The most commonly used CDI architecture is the flow-by cell, which employs film electrodes with a spacer channel placed in between, through which the solution flows along the electrodes [2].…”

Section: Introductionmentioning

confidence: 99%

Desalination with porous electrodes : Mechanisms of ion transport and adsorption

Dykstra¹

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Redox-electrodes for selective electrochemical separations

Cited by 139 publications

References 151 publications

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

Asymmetric Redox‐Polymer Interfaces for Electrochemical Reactive Separations: Synergistic Capture and Conversion of Arsenic

Desalination with porous electrodes : Mechanisms of ion transport and adsorption

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