Growth and dissolution of NaO2 in an ether-based electrolyte as the discharge product in the Na-O-2 cell

The deposition and dissolution of sodium superoxide (NaO2) was investigated by atomic force microscopy.</p

Shell isolated nanoparticles for enhanced Raman spectroscopy studies in lithium-oxygen cells

A critical and detailed assessment of using Shell Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS) on different electrode substrates was carried out, providing relative enhancement factors, as well as an evaluation of the distribution of shell-isolated nanoparticles upon the electrode surfaces. The chemical makeup of surface layers formed upon lithium metal electrodes and the mechanism of the oxygen reduction reaction on carbon substrates relevant to lithium–oxygen cells are studied with the employment of the SHINERS technique. SHINERS enhanced the Raman signal at these surfaces showing a predominant Li2O based layer on lithium metal in a variety of electrolytes. The formation of LiO2and Li2O2, as well as degradation reactions forming Li2CO3, upon planar carbon electrode interfaces and upon composite carbon black electrodes were followed under potential control during the reduction of oxygen in a non-aqueous electrolyte based on dimethyl sulfoxide.</p

Influence of Tetraalkylammonium Cation Chain Length on Gold and Glassy Carbon Electrode Interfaces for Alkali Metal–Oxygen Batteries

Fundamental studies of dioxygen electrochemistry relevant to metal–air batteries commonly require conductive supporting salts, such as tetraalkylammonium, to sustain redox processes in nonaqueous electrolytes. Electrochemical analysis of the formation and oxidation of superoxide on glassy carbon and gold working electrodes has shown a decrease in reversibility and lowering of the oxygen reduction rate constant when tetraalkylammonium cation alkyl chain length is increased. Probing interfacial regions on Au using in situ surface enhanced Raman spectroscopy (SERS) provides evidence that this is caused by the changing adsorption characteristics of tetralkylammonium cations under negative potentials. These effects are heightened with longer alkyl chain lengths, therefore reducing the reversibility of superoxide formation and dioxygen evolution. From these observations it can be established that shorter chain tetraalkylammonium cations while retaining necessary conductive support: (1) enhance reversibility and rate of superoxide formation and oxidation and (2) for in situ SERS, have lower preference for adsorption, thus improving experimental detection of superoxide at the Au electrode interface

Adsorption, surface relaxation and electrolyte structure at Pt(111) electrodes in non-aqueous and aqueous acetonitrile electrolytes.

In situ electrochemical surface X-ray diffraction was employed to investigate the atomic scale structure of the electrochemical double layer and the relaxation at the Pt(111) electrode surface in non-aqueous and aqueous acetonitrile electrolytes under potential control. The X-ray measurements provide insight into the potential-dependence of the interface structure by combining potentiodynamic measurements (X-ray voltammetry) with potentiostatic measurements (crystal truncation rod data) to probe both the metal and electrolyte sides of the interface. The crystal truncation rod measurements are consistent with the potential dependent reorientation of acetonitrile in the absence of water and a parallel arrangement in the presence of water. As acetonitrile concentration increases, the electron density closest to the electrode surface also increases. Finally, Pt surface relaxation in a range of aqueous and non-aqueous solvents is discussed in general with regards to the structure of the electrochemical double layer

Potential Dependence of Surfactant Adsorption at the Graphite Electrode/Deep Eutectic Solvent Interface

Copyright © 2019 American Chemical Society. Atomic force microscopy and cyclic voltammetry are used to probe how ionic surfactant adsorbed layer structure affects redox processes at deep eutectic solvent (DES)/graphite interfaces. Unlike its behavior in water, sodium dodecyl sulfate (SDS) in DESs only adsorbs as a complete layer of hemicylindrical hemimicelles far above its critical micelle concentration (CMC). Near the CMC it forms a tail-to-tail monolayer at open-circuit potential (OCP) and positive potentials, and it desorbs at negative potentials. In contrast, cetyltrimethylammonium bromide (CTAB) adsorbs as hemimicelles at low concentrations and remains adsorbed at both positive and negative potentials. The SDS horizontal monolayer has little overall effect on redox processes at the graphite interface, but hemimicelles form an effective and stable barrier. The stronger solvophobic interactions between the C16 versus C12 alkyl chains in the DES allow CTAB to self-assemble into a robust coating at low concentrations and illustrate how the structure of the DES/electrode interface and electrochemical response can be engineered by controlling surfactant structure