Probing electrolyte influence on CO2 reduction in aprotic solvents

Selective CO2 capture and electrochemical conversion is an important tool in the fight against climate change. Industrially, CO2 is captured using a variety of aprotic solvents due to their high CO2 solubility. However, most research efforts on electrochemical CO2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER; making it important to develop strategies that enable integrated CO2 capture and conversion in an aprotic solvent. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO2 reduction is unclear. In this work, we show that bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst-electrolyte interface. We study different TBA (tetrabutylammonium) salts in two electrolyte systems with glyme-ethers (e.g., 1,2 dimethoxyethane or DME) and dimethylsulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that form within the electrolyte and show how ion-pair formation is prevalent in DME electrolytes and is dependent on anion type. More importantly, we show as ion-pair formation decreases within the electrolyte, CO2 current densities increases, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where ion-pair fraction does not change with anion type (such as in DMSO), a smaller influence of solvation was observed on CO2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte design for efficient and selective CO2 conversion to desired fuels and chemicals

Lithium-Titanate As Electrode Material for Aprotic Systems

This article briefly describes experiments which investigate the mutual compatibility of aprotic solvents with higher fire safety and Lithium Titanate Oxide (LTO) as the negative electrode material for lithium-ion batteries. The work follows the current trend of enhancing fire safety by using new kinds of aprotic solvents along with a new generation of electrode materials which fulfil the intended using of lithium-ion batteries for high power applications, e.g. electric vehicle propulsion. In our work, the examiner of using sulfolane electrolyte (SL) and Li4Ti5O12 (LTO) under various ambient temperatures. The influence of electrolyte on the proper operation and stability of negative electrode material was considered. The measurements were performed in the temperature range from 25 °C up to 80 °C with half-cell connection. Our main objective of these experiments was to prove and investigate a proper operation of an aprotic electrolyte with higher fire safety together with LTO negative material under high ambient temperatures.

Transparent Self-Cleaning Coatings Based on Colorless Polyimide/Silica Sol Nanocomposite

We herein report transparent self-cleaning coatings based on polyimide-fluorinated silica sol (PIFSS) nanocomposite. Polyamic acid-silica sol (PASS) suspensions were synthesized by adding four different amounts of a silica sol suspension to each end-capped polyamic acid solution. The PASS suspensions were spin-coated on glass slides, thermally imidized and treated with triethoxy-1H,1H,2H,2H-perfluorodecylsilane (TEFDS) to prepare PIFSS coatings. The PIFSS coatings showed high resistance to separation from glass substrates and thermal stability. Furthermore, the PIFSS coatings on the glass substrate could be cleanly removed using polar aprotic solvents and repeated coating was possible. As the amount of silica sol particles in the PIFSS coating was increased, the hydrophobic contact angle increased. Among them, PIFSS-10 and PIFSS-15 coatings showed nearly superhydrophobic contact angles (144° and 148°, respectively) and good self-cleaning property. It was confirmed by SEM and AFM studies that their hydrophobic and self-cleaning properties are due to uniform particle distribution and relatively high surface roughness. PIFSS-10 coating showed a high transmittance value (88%) at 550 nm and good self-cleaning property, therefore suitable as a transparent self-cleaning coating. The advantages of the coating are that the fabrication process is simple, and the substrate is reusable. The PIFSS coating is expected to be applied in solar cell panels, windows, lenses and safety goggles.

Formazans: a Structural and Spectroscopic Study of 3-Substituted-1,5-Diphenylformazans

<p>A series of thirteen isomeric 1,5-diphenylformazans have been structurally characterised both in the solid state and in solution by the combined techniques of x-ray crystallography, nuclear magnetic resonance, Raman, mass and absorption spectroscopies. 1,5-Diphenylformazan is known to exist in the anti, s-trans configuration in the solid state and this is shown to be the solution dominant species. In aprotic solvents an equilibrium involving the anti, s-trans and syn, s-cis configurations is evidenced. 3-Methyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C14H14N4 belongs to the monoclinic space group P2/c, a = 8.133(1), b = 19.085(4), c = 9.364(2) A, beta = 105.93 degrees,U = 1397.6(5) A3, Z = 4. The anti, s-trans configuration of the solid state is also preferred in solution where it is in equilibrium with the syn, s-cis configuration. 3-Ethyl-1,5-diphenylformazan exists in two isomers in the solid state, both of which have been characterised by an x-ray crystal analysis. The red isomer of 3-ethyl-1,5-diphenylformazan belongs to the orthorhombic space group P2l2l2l and adopts the syn, s-trans configuration in the solid state. The orange, light stable isomer of 3-ethyl-1,5-diphenylformazan belongs to the monoclinic space group P2l/c and adopts the anti, s-trans configuration in the solid state. The rate of return of the photo-activated orange isomer to the dark-stable red isomer follows first order kinetics dependent upon the total concentration of the formazan and the water content of the solvent. 3-Tertiary-butyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C17H20N4, belongs to the monoclinic space group P2/c, a = 11.235(3), b = 20.117(5), c = 14.176(3) A, beta = 92.14(2) degrees, U = 3202(1) A3, Z = 8. The syn, s-cis configuration of the solid state is maintained in solution. 1,3,5-Triphenylformazan is shown to exist in two red forms in the solid state. The syn, s-cis and syn, s-trans isomers are both present in the crystalline sample. These isomers are also evident in solution with the syn, s-trans configuration becoming more dominant in aprotic solvents. 1,5-Diphenylformazan reacts with bromine in solution in a single reaction to give di(3-bromo-1,5-diphenyltetrazolium)-decabromide and 3-bromo-1,5-di-para-phenylformazan, both of which have been characterised by an x-ray crystal analysis. C13H10.6N4Br5.3 belongs to the triclinic space group Pl, a = 8.572(1), b = 9.711(1), c = 14.166(3) A, alpha = 75.18(1), beta = 89.84(1), gamma = 70.42(1) degrees, Z = 2. Stacks of anti-parallel pairs of 3-bromo-1,5-diphenyltetrazolium cations are interleaved by pairs of Br102- anions. The polybromide represents a new type of polyhalogen network for bromine, Br102-, the Raman spectrum of which has been recorded for the first time. C13H9N4Br3 belong to the orthorhombic space group Pnma, a = 7.343(2), b = 32.793(12), c = 5.912(1) A, Z = 4. The formazan adopts the anti, s-trans configuration in the solid state. 3-Chloro-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. Preliminary results indicate that the formazan adopts the anti, s-trans configuration in the solid state. 3-Mercapto-1,5-diphenylformazan is shown to exist in the anti, s-trans configuration in CDCl3, solution. 3-Methylthio-1,5-diphenylformazan is shown to exist in an equilibrium mixture of syn, s-trans and anti, s-trans configurations in solution. The ratio of the two isomers is approximately equal. 3-Ethylthio-1,5-diphenylformazan exists in two isomers in the solid state, one of which has been characterised by an x-ray crystal analysis. Preliminary results indicate that the orange isomer of 3-ethylthio-1,5-diphenylformazan. C15H16N4S belongs to the monoclinic space group P2l/a, a = 11.027(6). b = 8.627(7), c = 15.487(8) A, b = 93.70(5) degrees, U = 1470 A3, Z = 4, and exists in the anti, s-trans configuration on the solid state. The orange and red isomers are both present in an equilibrium mixture in solution. The red isomer is shown to exist in the syn, s-trans configuration in the solid. 3-isopropylthio-1,5-diphenylformazan is shown to exist in an equilibrium mixture of anti, s-trans and syn, s-trans configurations in solution. 1-Methyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C14H14N4 belongs to the monoclinic space group 12/1, a = 28.402(7), b = 5.640(1), c = 15.688(4) A, beta = 97.34 degrees, U = 2493(1) A3, Z = 8. The formazan adopts the anti, s-trans configuration in the solid state. The formazan retains its configurational integrity in both protic and aprotic solutions. The excitation profile of the Raman active phonons based upon coupled vibrations of the formazan backbone indicate a maximum corresponding to the absorption spectra in both the solid state and in solution. Preliminary results of a kinetic investigation of some primary metal dithizonates indicate that the thermal-path return is strictly first order. The mechanism would appear to be essentially similar to that operating in 3-ethyl-1,5-diphenylformazan. The mass spectra of the series of formazan follow similar splitting schemes irrespective of the solid-state configuration.</p>

Formazans: a Structural and Spectroscopic Study of 3-Substituted-1,5-Diphenylformazans

<p>A series of thirteen isomeric 1,5-diphenylformazans have been structurally characterised both in the solid state and in solution by the combined techniques of x-ray crystallography, nuclear magnetic resonance, Raman, mass and absorption spectroscopies. 1,5-Diphenylformazan is known to exist in the anti, s-trans configuration in the solid state and this is shown to be the solution dominant species. In aprotic solvents an equilibrium involving the anti, s-trans and syn, s-cis configurations is evidenced. 3-Methyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C14H14N4 belongs to the monoclinic space group P2/c, a = 8.133(1), b = 19.085(4), c = 9.364(2) A, beta = 105.93 degrees,U = 1397.6(5) A3, Z = 4. The anti, s-trans configuration of the solid state is also preferred in solution where it is in equilibrium with the syn, s-cis configuration. 3-Ethyl-1,5-diphenylformazan exists in two isomers in the solid state, both of which have been characterised by an x-ray crystal analysis. The red isomer of 3-ethyl-1,5-diphenylformazan belongs to the orthorhombic space group P2l2l2l and adopts the syn, s-trans configuration in the solid state. The orange, light stable isomer of 3-ethyl-1,5-diphenylformazan belongs to the monoclinic space group P2l/c and adopts the anti, s-trans configuration in the solid state. The rate of return of the photo-activated orange isomer to the dark-stable red isomer follows first order kinetics dependent upon the total concentration of the formazan and the water content of the solvent. 3-Tertiary-butyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C17H20N4, belongs to the monoclinic space group P2/c, a = 11.235(3), b = 20.117(5), c = 14.176(3) A, beta = 92.14(2) degrees, U = 3202(1) A3, Z = 8. The syn, s-cis configuration of the solid state is maintained in solution. 1,3,5-Triphenylformazan is shown to exist in two red forms in the solid state. The syn, s-cis and syn, s-trans isomers are both present in the crystalline sample. These isomers are also evident in solution with the syn, s-trans configuration becoming more dominant in aprotic solvents. 1,5-Diphenylformazan reacts with bromine in solution in a single reaction to give di(3-bromo-1,5-diphenyltetrazolium)-decabromide and 3-bromo-1,5-di-para-phenylformazan, both of which have been characterised by an x-ray crystal analysis. C13H10.6N4Br5.3 belongs to the triclinic space group Pl, a = 8.572(1), b = 9.711(1), c = 14.166(3) A, alpha = 75.18(1), beta = 89.84(1), gamma = 70.42(1) degrees, Z = 2. Stacks of anti-parallel pairs of 3-bromo-1,5-diphenyltetrazolium cations are interleaved by pairs of Br102- anions. The polybromide represents a new type of polyhalogen network for bromine, Br102-, the Raman spectrum of which has been recorded for the first time. C13H9N4Br3 belong to the orthorhombic space group Pnma, a = 7.343(2), b = 32.793(12), c = 5.912(1) A, Z = 4. The formazan adopts the anti, s-trans configuration in the solid state. 3-Chloro-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. Preliminary results indicate that the formazan adopts the anti, s-trans configuration in the solid state. 3-Mercapto-1,5-diphenylformazan is shown to exist in the anti, s-trans configuration in CDCl3, solution. 3-Methylthio-1,5-diphenylformazan is shown to exist in an equilibrium mixture of syn, s-trans and anti, s-trans configurations in solution. The ratio of the two isomers is approximately equal. 3-Ethylthio-1,5-diphenylformazan exists in two isomers in the solid state, one of which has been characterised by an x-ray crystal analysis. Preliminary results indicate that the orange isomer of 3-ethylthio-1,5-diphenylformazan. C15H16N4S belongs to the monoclinic space group P2l/a, a = 11.027(6). b = 8.627(7), c = 15.487(8) A, b = 93.70(5) degrees, U = 1470 A3, Z = 4, and exists in the anti, s-trans configuration on the solid state. The orange and red isomers are both present in an equilibrium mixture in solution. The red isomer is shown to exist in the syn, s-trans configuration in the solid. 3-isopropylthio-1,5-diphenylformazan is shown to exist in an equilibrium mixture of anti, s-trans and syn, s-trans configurations in solution. 1-Methyl-1,5-diphenylformazan has been characterised by an x-ray crystal analysis. C14H14N4 belongs to the monoclinic space group 12/1, a = 28.402(7), b = 5.640(1), c = 15.688(4) A, beta = 97.34 degrees, U = 2493(1) A3, Z = 8. The formazan adopts the anti, s-trans configuration in the solid state. The formazan retains its configurational integrity in both protic and aprotic solutions. The excitation profile of the Raman active phonons based upon coupled vibrations of the formazan backbone indicate a maximum corresponding to the absorption spectra in both the solid state and in solution. Preliminary results of a kinetic investigation of some primary metal dithizonates indicate that the thermal-path return is strictly first order. The mechanism would appear to be essentially similar to that operating in 3-ethyl-1,5-diphenylformazan. The mass spectra of the series of formazan follow similar splitting schemes irrespective of the solid-state configuration.</p>

Solvent effect on the absorption and emission spectra of carbon dots: evaluation of ground and excited state dipole moment

Background Carbon dots (C-dots) are photoluminescent nanoparticles with less than 10 nm in size. Today, many studies are performed to exploit the photoluminescence (PL) property of carbon dots, and our focus in this study is to estimate the dipole moment of carbon dots. For reaching our aims, C-dots were synthesized and dissolved in the different solvents. Results Carbon dots with intense photoluminescence properties have been synthesized by a one-step hydrothermal method from a carbon bio-source. In this research, we report on the effect of aprotic solvents on absorption and fluorescence spectra and dipole moments of C-dots dispersed in a range of many aprotic solvents with various polarity and dielectric constant at room temperature. The change in the value of dipole moment was estimated by using the Stokes shifts. The difference between the dipole moment of the excited state and the ground state was shown using an extended form of Lippert equations by Kawski and co-workers. Conclusions The values found for μg = 1.077 D, and μe = 3.157 D, as well as the change in the dipole moments. The results showed that the dipole moment of the excited state is more than the ground state, indicating a high density and redistribution of electrons in the excited state. Finally, the quantum yield of C-dots in the eclectic aprotic solvents was communicated and discussed.

Crosslinked Sodium Alginate as a Material for Nanolfiltration Protonic and Aprotonic Solvents

In this work, for the first time, salts of bivalent and trivalent metals were used as crosslinking agents for nanofiltration membranes based on sodium alginate. The developed membranes were investigated for chemical stability in protic and aprotic solvents, the dependence of the permeability of these solvents on their sorption into the membrane material was obtained. The separating properties of membranes based on sodium alginate crosslinked with metal cations were investigated. The retention coefficient of the model substance with a molecular weight of 626 g/mol, dissolved in ethanol, was 97%.