Abstract
Electrode materials which undergo anion insertion are a void in the materials innovation landscape and a missing link to energy efficient electrochemical desalination. In recent years layered hydroxides (LHs) have been studied for a range of electrochemical applications, but to date have not been considered as electrode materials for anion insertion electrochemistry. Here, we show reversible anion insertion in a LH for the first time using Co and Co-V layer hydroxides. By pairing in situ synchrotron and quartz crystal microbalance measurements with a computational unified electrochemical band-diagram description, we reveal a previously undescribed anion-insertion mechanism occurring in Co and Co-V LHs. This proof of concept study demonstrates reversible electrochemical anion insertion in LHs without significant material optimization. These results coupled with our foundational understanding of anion insertion electrochemistry establishes LHs as a materials platform for anion insertion electrochemistry with the potential for future application to electrochemical desalination.
Highlights
To date, silver is the leading material which has been used to enhance anion uptake during CDI
We contend that layered hydroxides (LHs) may be a promising option for anion insertion electrochemistry considering their use as anion exchange materials[23], as well as their facile synthesis and modularity of possible chemical composition[24] which allow for tunable chemical properties
While the Mg-Al layered double hydroxides (LDHs) synthesis is robust and well-studied, we do not expect Mg-Al LDHs to be useful as anion insertion electrodes because Mg and Al do not undergo redox electrochemistry within the potential limits of water stability
Summary
Matthias J.Young 1,2,3,4, Tatyana Kiryutina[2], Nicholas M. In recent years layered hydroxides (LHs) have been studied for a range of electrochemical applications, but to date have not been considered as electrode materials for anion insertion electrochemistry. Identifying new materials for anion insertion electrochemistry is a necessary first step to enable enhanced desalination efficiency using membrane-free CDI cell designs. The study of anion insertion electrode materials is a new frontier which promises to lead to other exciting electrochemical technologies including anion-based batteries or enhanced anion exchange membranes. Coupling computational results within the UEB framework with in situ experimental measurements including quartz crystal microbalance (QCM), high energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis and X-ray absorption spectroscopy (XAS) provides compelling evidence of anion insertion electrochemistry in LHs for potential future use in water desalination applications
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