During the course of investigating carbonaceous materials for the active materials of Li-ion batteries (LIB) or supercapacitors (SPC) we have found interesting properties and behaviors of the carbon in contact with an electrolyte containing Li+. In this article the author would like to exhibit these attractive matters. Especially use of carbon fiber (CF) attracted our attention since we can use a single fiber as the working electrode, which enables us to measure not only the conductivity change but also the volume change during Li insertion/extraction. Determination of the lithium diffusion coefficient in carbon could be performed with ease. Surprisingly propylene carbonate showed no decomposition during cathodic polarization of graphite in propylene carbonate electrolyte when we use a single graphitzed fiber. On the other hand, by the use of rounded graphite particle we suggested presence of holes on the graphene layer. We proved that homogeneous distribution of conductivity over the surface of coated electrode is the key factor to keep long cycle life.
We describe an improvement of the detectable range of glucose oxidase (GOx)-based microsensors to higher concentrations. Oxygen consumed by the enzyme reaction of GOx was detected cathodically by the microelectrode modified with poly(dimethylsiloxane) (PDMS) and GOx layers. PDMS was used to prevent the permeation of hydrogen peroxide that was produced by the enzyme reaction. The prepared microsensors were positioned above microband electrodes which were used to produce oxygen by the electrolysis of water, allowing a high oxygen concentration (0.8 mM) to be maintained around the microsensors. By applying this system, the detectable concentration range for glucose was extended up to 20 mM.
New lithium imide salts have been studied using computational chemistry methods. Intrinsic anion oxidation potentials and ion pair dissociation energies are presented for six lithium sulfonyl imides (R-O2S-N-SO2-R) and six lithium phosphoryl imides (R2-OP-N-PO-R2), as a function of -F, -CF3, and -C≡N substitution. The modelled properties are used to estimate the electrochemical oxidation stability of the anions and the relative ease of charge carrier creation in lithium battery electrolytes. The results show that both properties are improved with cyano-substitution, which in part is corroborated when comparing with other classes of lithium salts. However, the comparison also shows ambiguous oxidation stability results for cyano-substituted reference salts of the type PFx(CN)6−x− and BFx(CN)4−x−, using two different approaches – we present a tentative explanation for this. For the imide anions and PF6−, the bond dissociation energy is introduced as a third property, to gauge the thermal stability of the imide anions. The results suggest that the C-S and C-P bonds are the most liable to break and that the thermal stability is inversely related to the ion pair dissociation energy.
Pentakis(diethylamido)tantalum (PDEAT) was synthesized by electrochemical reaction involving diethylamide with a sacrificial tantalum anode and stainless steel cathode in the presence of tetraethylammonium bromine as the conductive additive and acetonitrile as the inert support electrolyte. The condensates were isolated by the reduced pressure distillation of as-synthesized crude PDEAT below 5 kPa. The final product was characterized by FT-IR and NMR spectroscopy. The thermal properties of the resulting PDEAT were analyzed by TG-DTG. Results indicate that the resulting compound was indeed PDEAT. The vapor pressure of the compound was calculated from the Langmuir equation, while the enthalpy of vaporization was calculated from vapor pressure-temperature data using the Clausius-Clapeyron equation. The concentration of the impurities in the sample were detected via ICP-Mass spectroscopy, and it was found that the purity of the compound synthesized could reach 99.995%.
Detectable sensitivity for immobilized enzymes was improved using a constant-distance mode of scanning electrochemical microscopy (SECM). Redox species generated by an enzyme reaction captured via immunorecognition were detected with a microelectrode used as a probe. The probe maintained considerably close to the target surface (50 nm) allowed the enhancement of the current response because of cycling of redox species between the probe and the captured enzymes. The sensitivity of di(n-butyl)phthalate detection with a competitive assay by using constant-distance mode SECM was at least one order of magnitude higher than that of the probe scanned in a constant z-position.