Ion Bridging by Carbon Dioxide Facilitates Electrochemical Energy Storage at Charged Carbon–Ionic–Liquid Interfaces

Abstract Solvent free ionic liquid (IL) electrolytes facilitate high‐voltage supercapacitors with enhanced energy density, but their complex ion arrangement and through that the electrochemical properties, are limited by strong Coulombic ordering in the bulk state and like‐charged ion repulsion at electrified interfaces. Herein, a unique interfacial phenomenon resulting from the presence of carbon dioxide loaded in 1‐Ethyl‐3‐methylimidazoliumtetrafluorborate electrolyte that simultaneously couples to IL ions and nitrogen‐doped carbonaceous electrode is reported. The adsorbed CO 2 molecule polarizes and mitigates the electrostatic repulsion among like‐charged ions near the electrified interface, leading to an ion “bridge effect” with increased interfacial ionic density and significantly enhanced charge storage capability. The unpolarized CO 2 possessing a large quadrupole moment further reduces ion coupling, resulting in higher conductivity of the bulk IL and improved rate capability of the supercapacitor. This work demonstrates polarization‐controlled like‐charge attraction at IL–electrode–gas three‐phase boundaries, providing insights into manipulating complex interfacial ion ordering with small polar molecule mediators.Solvent‐free ionic liquid (IL) electrolytes enable high‐voltage and high‐energy‐density applications. The proposed bridge effect with CO 2 loaded in an IL electrolyte acting as a mediator on the nitrogen‐doped electrode surface, alleviates the undesired Coulombic ordering and interfacial like‐charged ion repulsion. By breaking the limitation of interfacial ion packing density, this effect results in a significant enhancement of charge storage capability. imag

Improving the Stability of Supercapacitors at High Voltages and High Temperatures by the Implementation of Ethyl Isopropyl Sulfone as Electrolyte Solvent

Abstract Two of the main weaknesses of modern electric double‐layer capacitors are the rather limited ranges of operating voltage and temperature in which these devices do not suffer from the occurrence of irreversible decomposition processes. These parameters are strongly interconnected and lowering the operating voltage when increasing the temperature is unavoidable, so as to protect the electric double‐layer capacitor from damage. With the aim to maintain the operating voltage as high as possible at elevated temperatures, in this study, the application of ethyl isopropyl sulfone as an electrolyte solvent for electric double‐layer capacitors is presented. It is shown that ethyl isopropyl sulfone‐based electrolytes display excellent thermal and electrochemical stability enabling high capacitance retention after floating tests for 500 h at 60 and 80 °C, e.g. 68% at 3.4 V at 60 °C. A possible reason for the above‐average stability is that decomposition products of ethyl isopropyl sulfone can deposit on the electrode surface which may act as a passivation layer and prevent further degradation.Ethyl isopropyl sulfone is an interesting electrolyte solvent for electric double‐layer capacitors in high‐temperature surroundings. Forming a protective passive layer on the electrode surface, ethyl isopropyl sulfone offers high thermal and electrochemical stability for supercapacitors at temperatures of up to 80 °C and voltages of up to 3.4 V. imag

Effects of Carbon Pore Size on the Contribution of Ionic Liquid Electrolyte Phase Transitions to Energy Storage in Supercapacitors

Recent research on ionic liquid electrolyte-based supercapacitors indicated the contribution of phase transitions of the electrolytes at high cell voltages to the energy stored. This mechanism can be exploited to significantly increase the energy density of supercapacitors, which up to now remains their major drawback. It was found that these ordering transitions require the presence of mesopores within the carbon electrode materials and that porosity in general is a key factor to trigger them, but details of the mechanism remains unexplained. To get a more profound understanding of this phenomenon, carbon materials with different pore diameters and volumes were synthesized and the effect of those properties on the phase transitions in the ionic liquids was studied by means of cyclic voltammetry. A clear correlation between the peak current and the mesopore volume is revealed and an optimal pore diameter was determined, exceeding which does not improve the phase transition behavior. These findings are useful as guidelines for the rational design of carbon mesopores in order to utilize the new energy storage modes which are neither fully capacitive, nor redox-based

Improvement of Oxygen-Depolarized Cathodes in Highly Alkaline Media by Electrospinning of Poly(vinylidene fluoride) Barrier Layers

Oxygen‐depolarized cathodes (ODC) were developed for chlor‐alkali electrolysis to replace the hydrogen evolution reaction (HER) by the oxygen reduction reaction (ORR) providing electrical energy savings up to 30 % under industrially relevant conditions. These electrodes consist of micro sized silver grains and polytetrafluoroethylene, forming a homogeneous electrode structure. In this work, we report on the modification of ODCs by implementing an electrospun layer of hydrophobic poly(vinylidene fluoride) (PVDF) into the ODC structure, leading to a significantly enhanced ORR performance. The modified electrodes are physically characterized by liquid flow porometry, contact angle measurements and scanning electron microscopy. Electrochemical characterization is performed by linear sweep voltammetry and chronopotentiometry. The overpotential for ORR at application near conditions could be reduced by up to 75 mV at 4 kA m−2 and 135 mV at a higher current density of 9.5 kA m−2. Consequently, we propose that modifying ODCs by electrospinning is an effective and cost‐efficient way to further reduce the energy demand of the ORR in highly alkaline media

Organometallic gold(III) complexes with tridentate halogen‐substituted thiosemicarbazones: Effects of halogenation on cytotoxicity and anti‐parasitic activity

Chemical properties and biological activity of Au(III) compounds obtained from dichlorido[2‐(dimethylaminomethyl)phenyl‐C1,N]gold(III), [Au(damp‐C1,N)Cl2], and halogenated, potentially tridentate thiosemicarbazones have been studied. The results of this work show that the complexation of the halogenated thiosemicarbazones with Au(III) enhances their stability against hydrolysis and retains or enhances their anti‐parasitic activity. Fluorination in the periphery of the ligands has expectedly no influence on the structural chemistry of the obtained Au(III) complexes, but modulates their biological behaviour. Best results with a remarkably high selectivity index for the trypomastigote form of Trypanosoma cruzi were obtained with the complex containing the ligand, which presents a 3,5‐fluorine substitution in meta‐position of an aromatic ring, [Au(dampH)(L‐3,5‐F)]Cl

Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In‐Situ and Ex‐Situ Solid‐State NMR

In this work, we report on an improved cell assembly of cylindrical electrochemical cells for ²³Na in‐situ solid‐state NMR (ssNMR) investigations. The cell set‐up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. ²³Na in‐situ ssNMR monitors the sodiation/desodiation of a Na|NaPF₆|HC cell (cell 1) over a period of 22 days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution ²³Na ex‐situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na|NaPF₆|HC cell (cell 2) is sodiated for 11 days achieving a capacity of 220 mAh/g. ²³Na ex‐situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi‐metallic sodium species next to ionic sodium species. This observation of quasi‐metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material

Mechanistic insights into the reversible lithium storage in an open porous carbon via metal cluster formation in all solid-state batteries

Porous carbons are promising anode materials for next generation lithium batteries due to their large lithium storage capacities. However, their highsloping capacity during lithiation and delithiation as well as capacity fading due to intense formation of solid electrolyte interphase (SEI) limit their gravimetric and volumetric energy densities. Herein we compare a microporous carbide derived carbon material (MPC) as promising future anode for all solid state batteries with a commercial high performance hard carbon anode. The MPC obtains high and reversible lithiation capacities of 1000 mAh g 1 carbon in half cells exhibiting an extended plateau region near 0 V vs. Li/Liþ preferable for full cell application. The well defined microporosity of the MPC with a specific surface area of >1500 m2 g 1 combines well with the argyrodite type electrolyte (Li6PS5Cl) suppressing extensive SEI formation to deliver high coulombic efficiencies. Preliminary full cell measurements vs. nickel rich NMC cathodes (LiNi0.9Co0.05Mn0.05O2) provide a considerably improved average potential of 3.76 V leading to a projected energy density as high as 449 Wh kg 1 and reversible cycling for more than 60 cycles. 7Li Nuclear Magnetic Resonance spectroscopy was combined with ex situ Small Angle X ray Scattering to elucidate the storage mechanism of lithium inside the carbon matrix. The formation of extended quasi metallic lithium clusters after electrochemical lithiation was revealed

SiCN Ceramics as Electrode Materials for Sodium/Sodium Ion Cells – Insights from ²³Na In‐Situ Solid‐State NMR

Polymer-derived silicon carbonitride ceramic (SiCN) is used as an electrode material to prepare cylindrical sodium/sodium ion cells for solid-state NMR investigations. During galvanostatic cycling structural changes of the environment of sodium/sodium ions are investigated by applying ²³Na in-situ solid-state NMR. Changes of the signals assigned to sodium metal, intercalated sodium cation and sodium cation originating from the electrolyte are monitored as well as the occurrence of an additional signal in the region of metallic sodium. The intensity of this additional signal changes periodically with the cycling process indicating the reversibility of structures formed and deformed during the galvanostatic cycling. To identify interactions of sodium/sodium ions with the SiCN electrode materials, the cycled SiCN material is studied by ²³Na ex-situ MAS NMR at high spinning rates of 20 and 50 kHz to obtain appropriate spectral resolution

Insights into the sodiation mechanism of hard carbon-like materials from electrochemical impedance spectroscopy

To render the sodium ion battery (SIB) competitive among other technologies, the processes behind sodium storage in hard carbon anodes must be understood. For this purpose, electrochemical impedance spectroscopy (EIS) is usually undervalued, since fitting the spectra with equivalent circuit models requires an a priori knowledge about the system at hand. The analysis of the distribution of relaxation times (DRT) is an alternative, which refrains from fitting arbitrarily nested equivalent circuits. In this paper, the sodiation and desodiation of a hard carbon anode is studied by EIS at different states of charge (SOC). By reconstructing the DRT function, highly resolved information on the number and relative contribution of individual electrochemical processes is derived. During the sloping part of the sodiation curve, mass transport is found to be the most dominant source of resistance but rapidly diminishes when the plateau phase is reached. An equivalent circuit model qualitatively reproducing the experimental data of the sloping region was built upon the DRT results, which is particularly useful for future EIS studies on hard carbon SIB anodes. More importantly, this work contributes to establish EIS as a practical tool to directly study electrode processes without the bias of a previously assumed model

Polyoxometalate-Modified Amphiphilic Polystyrene-<i>block</i>-poly(2-(dimethylamino)ethyl methacrylate) Membranes for Heterogeneous Glucose to Formic Acid Methyl Ester Oxidation

Herein, we present a new heterogeneous catalyst active toward glucose to formic acid methyl ester oxidation. The catalyst was fabricated via electrostatic immobilization of the inorganic polyoxometalate HPA-5 catalyst H8[PMo7V5O40] onto the pore surface of amphiphilic block copolymer membranes prepared via non-solvent-induced phase separation (NIPS). The catalyst immobilization was achieved via wet impregnation due to strong coulombic interactions between protonated tertiary amino groups of the polar poly(2-(dimethylamino)ethyl methacrylate) block and the anionic catalyst. Overall, three sets of five consecutive catalytic cycles were performed in an autoclave under 90 °С and 11.5 bar air pressure in methanol, and the corresponding yields of formic acid methyl ester were quantified via head-space gas chromatography. The obtained results demonstrate that the membrane maintains its catalytic activity over multiple cycles, resulting in high to moderate yields in comparison to a homogeneous catalytic system. Nevertheless, presumably due to leaching, the catalytic activity declines over five catalytic cycles. The morphological and chemical changes of the membrane during the prolonged catalysis under harsh conditions were examined in detail using different analytic tools, and it seems that the underlying block copolymer is not affected by the catalytic process