The reduction of dioxygen in the presence of sodium cations can be tuned to give either sodium superoxide or sodium peroxide discharge products at the electrode surface. Control of the mechanistic ...direction of these processes may enhance the ability to tailor the energy density of sodium–oxygen batteries (NaO2: 1071 Wh kg−1 and Na2O2: 1505 Wh kg−1). Through spectroelectrochemical analysis of a range of non‐aqueous solvents, we describe the dependence of these processes on the electrolyte solvent and subsequent interactions formed between Na+ and O2−. The solvents ability to form and remove Na+‐O2−ads based on Gutmann donor number influences the final discharge product and mechanism of the cell. Utilizing surface‐enhanced Raman spectroscopy and electrochemical techniques, we demonstrate an analysis of the response of Na‐O2 cell chemistry with sulfoxide, amide, ether, and nitrile electrolyte solvents.
Solvents make the difference: A solvent‐dependent mechanism for the oxygen reduction reaction in the presence of sodium is reported. NaO2 is formed in high donor number solvents, and in low donor number solvents Na2O2 formation is observed.
Proton conduction is a fundamental process in biology and in devices such as proton exchange membrane fuel cells. To maximize proton conduction, three-dimensional conduction pathways are preferred ...over one-dimensional pathways, which prevent conduction in two dimensions. Many crystalline porous solids to date show one-dimensional proton conduction. Here we report porous molecular cages with proton conductivities (up to 10(-3) S cm(-1) at high relative humidity) that compete with extended metal-organic frameworks. The structure of the organic cage imposes a conduction pathway that is necessarily three-dimensional. The cage molecules also promote proton transfer by confining the water molecules while being sufficiently flexible to allow hydrogen bond reorganization. The proton conduction is explained at the molecular level through a combination of proton conductivity measurements, crystallography, molecular simulations and quasi-elastic neutron scattering. These results provide a starting point for high-temperature, anhydrous proton conductors through inclusion of guests other than water in the cage pores.
The development of selective electrocatalysts for CO2 reduction in water offers a sustainable route to carbon based fuels and feedstocks. However, molecular catalysts are typically studied in ...non-aqueous solvents, in part to avoid competitive H2 evolution. Ni(cyclam)2+ (1) is one of the few known electrocatalysts that operate in water and 30 years after its report its activity remains a rarely surpassed benchmark. Here we report that Ni(cyclam-CO2H)2+ (cyclam-CO2H = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid (2)) shows greatly enhanced activity versus1 for CO production. At pHs < pKa of the pendant carboxylic acid a large increase in catalytic activity occurs. Remarkably, despite the high proton concentration (pH 2), 2 maintains selectivity for CO2 reduction and is believed to be unique in operating selectively in such acidic aqueous solutions.
A one-pot sol-gel autocombustion synthesis for carbon coated antimony microparticles has been developed. The initial capacities of this material were 647mAhg−1Sb vs. Li and 527mAhg−1Sb vs. Na, with a ...rate capability (8C: 398 and 356mAhg−1Sb vs. Li and Na respectively) and cyclability (cycle 120 capacity retention: 86% vs. Li, 91% vs. Na). The sol-gel synthesised Sb was found to be superior to commercial Sb of similar particle size (ca. 5–50μm), which is attributed to carbon coating. In situ Raman analysis revealed differences between the sol-gel synthesised and commercial antimony materials, regarding their reversibility, during the 1st cycle, and additionally demonstrated that upon charge both materials do not return to a crystalline material, but instead to an amorphous phase represented by a broad feature centred at ca. 140cm−1.
Decarbonisation of energy will rely heavily, at least initially, on the use of lithium ion batteries for automotive transportation. The projected volumes of batteries necessitate the development of ...fast and efficient recycling protocols. Current methods are based on either hydrometallurgical or pyrometallurgical methods. The development of efficient separation techniques of waste lithium ion batteries into processable waste streams is needed to reduce material loss during recycling. Here we show a rapid and simple method for removing the active material from composite electrodes using high powered ultrasound in a continuous flow process. Cavitation at the electrode interface enables rapid and selective breaking of the adhesive bond, enabling an electrode to be delaminated in a matter of seconds. This enables the amount of material that can be processed in a given time and volume to be increased by a factor of approximately 100. It also produces a material of higher purity and value that can potentially be directly recycled into new electrodes.
Electric vehicle battery electrodes are delaminated ultra-fast using high-powered ultrasound, separating active materials from the foil current collectors.
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 Li
2
O based layer on lithium metal in a variety of electrolytes. The formation of LiO
2
and Li
2
O
2
, as well as degradation reactions forming Li
2
CO
3
, 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.
The deposition and dissolution of sodium superoxide (NaO2) was investigated by atomic force microscopy. Rectangular prisms consisting of 8 smaller sub-structures grew from NaO2 platelets, when ...discharged in 0.5 M NaClO4, diethylene glycol dimethyl ether on highly ordered pyrolytic graphite. During oxidation the 8 sub-structures are conserved. Ring-like structures of Na2CO3 of 200 nm diameter remain at the end of oxidation.
The deposition and dissolution of sodium superoxide (NaO
) was investigated by atomic force microscopy. Rectangular prisms consisting of 8 smaller sub-structures grew from NaO
platelets, when ...discharged in 0.5 M NaClO
, diethylene glycol dimethyl ether on highly ordered pyrolytic graphite. During oxidation the 8 sub-structures are conserved. Ring-like structures of Na
CO
of 200 nm diameter remain at the end of oxidation.
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.
Application of synchrotron X-ray scattering to probe the atomic structure of the interface between Pt(111) electrodes and non-aqueous acetonitrile electrolytes.
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.
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