Electrochemical methods using carbon electrodes are an attractive option for the detection and reduction of toxic Cr(vi) to benign Cr(iii) in drinking water.
The nature of the buffer influences the PCET step gating Cr(vi) reduction in water at pH 4.75, as well as the extent of deposition on carbon electrodes. Electrode activity is recovered without polishing, through a simple acid wash step.
New lithium electrolytes
compatible with high energy density cells
are critical for lithium metal battery applications, but dendrite
formation associated with the use of dilute organic electrolytes complicates
their realization. High-concentration electrolytes mitigate some of
the issues of the electrolytes but introduce additional problems,
such as low conductivity and high cost. Hence, pseudo-concentrated
electrolytes, wherein a co-solvent is added to a dilute electrolyte,
have been presented as a possible alternative to both dilute and concentrated
electrolytes. However, the effect that the co-solvent has on the electrolyte
properties at both macroscopic and microscopic levels is unknown.
Here, a study of the structure and electrochemical properties of two
electrolytes as a function of co-solvent concentration is presented
using an array of spectroscopies (FTIR, ATR–FTIR, and nuclear
magnetic resonance) and computational methods (density functional
theory calculations). The chosen electrolytes comprised two different
lithium salts (LiPF
6
and LiTFSI) in a mixture of dimethyl
carbonate (DMC) with 1,1,1,3,3-pentafluorobutane (PFB) as the co-solvent.
Our results show that in the case of the LiPF
6
/DMC electrolyte,
the addition of a co-solvent (PFB) with a larger dielectric constant
results in the strengthening of the lithium–anion interaction
and the formation of aggregate species since PFB does not interact
with the anion. Conversely, in the LiTFSI/DMC electrolyte, the co-solvent
appears to interact with the anion via hydrogen bonds, which leads
to the dissociation of contact ion pairs. The change in ionic speciation
of the electrolytes upon addition of PFB provides a reasonable framework
to explain the different trends in both the bulk and interfacial macroscopic
properties, such as conductivity, viscosity, and electrochemical stability.
Overall, our findings demonstrate that the interactions between the
anion and the co-solvent must be taken into consideration when adding
a co-solvent because they play a major role in determining the final
electrolyte properties.
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