High temperature, high energy density, and low loss dielectric films are promising candidates for miniaturized capacitors in electric vehicles and high-speed trains. However, single-component polymers could not achieve these desired properties simultaneously. Polymer multilayer films (MLFs), which combine a high dielectric constant polymer [e.g., poly(vinylidene fluoride) (PVDF)] and a high breakdown/low loss polymer [e.g., polycarbonate (PC)] in a unique layered structure, have the potential achieve them at the same time. In this work, the effects of PC glass transition temperature (T-g) on the dielectric insulation properties (breakdown strength and lifetime) were investigated at high temperatures of 100-150 degrees C. Three PC materials had T-g values of 145 (PC1), 165 (PC2), and 185 degrees C (PC3), respectively. It is observed that MLF-PC3 with the highest T-g of PC exhibited the highest Weibull direct/alternating current (DC/AC) breakdown strength and the longest DC/AC lifetime, whereas MLF-PC1 with the lowest T-g showed the lowest Weibull DC/AC breakdown strength and the shortest DC/AC lifetime. A high-temperature high-volage leakage current study revealed that MLF-PC3 exhibited the lowest bulk conductivity at all temperatures under different electric fields. The knowledge obtained from this study will help us design better MLFs with high performance for next-generation miniaturized capacitors.

Herein, a method is presented that allows quantitative determination of faradaic efficiencies for dinitrogen (N-2) generation during the electrochemical oxidation of hydroxylamine (NH2OH), fN2NH2OH, on a polycrystalline gold Au(poly) disk electrode in aqueous electrolytes over a wide pH range. This tactic involves the use of an impinging jet electrolyte configuration incorporating a gas porous ring connected in turn to a mass spectrometer. The actual amount of N-2 generated at the Au(poly) disk was assayed using the oxidation of hydrazine (N2H4) in aqueous phosphate buffer (pH 7). This redox process yields N-2 as the only product, allowing a direct correlation to be established between the changes in the partial pressures of N-2 and the current flowing through the disk electrode. An analysis of the data collected revealed a strong dependence of fN2NH2OHboth on pH and the applied potential. Although values of fN2NH2OH as high as 20 to 30 % were found in acid and neutral media over a narrow potential region, those in alkaline solution were far smaller in the entire potential range examined.

To search for alternative electrostrictive polymers and to understand the underlying mechanism, the structure-ferroelectric/electrostrictive property relationship for nylon-12-based poly(ether-b-amide) multiblock copolymers (PEBAX) is investigated. Two PEBAX samples are studied, namely, P6333 and P7033 with 37 and 25 mol.% of soft poly(tetramethylene oxide) (PTMO) blocks, respectively. In both samples, poorly hydrogen-bonded mesophase facilitates electric field-induced ferroelectric switching. Meanwhile, the longitudinal electrostrictive strain (S-1)-electric field (E) loops are obtained at 2 Hz. Different from conventional poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]-based terpolymers, uniaxially stretched nylon-12-based PEBAX samples exhibit negative S-1, that is, shrinking rather than elongation in the longitudinal direction. This is attributed to the unique conformation transformation of nylon-12 crystals during ferroelectric switching. Namely, at a zero electric field, crystalline nylon-12 chains adopt a more or less antiparallel arrangement of amide groups. Upon high-field poling, ferroelectric domains are enforced with more twisted chains adopting a parallel arrangement of amide groups. Meanwhile, extensional S-1 is observed for P6333 at electric fields above 150 MV m(-1). This is attributed to the elongation of the amorphous phases (i.e., amorphous nylon-12 and PTMO). Therefore, competition between shrinking S-1 from mesomorphic nylon-12 crystals (i.e., nanoactuation) and elongational S-1 from amorphous phases determines the ultimate electrostriction behavior in stretched PEBAX films.

Despite decades of research, no consensus has been reached regarding basic aspects of the mechanism of the oxygen reduction reaction (ORR) on Au electrodes in aqueous neutral and alkaline solutions1, 2., Most of the problems from an experimental viewpoint stem from the lack of techniques capable of identifying species believed to be involved as intermediates in the reaction, including both adsorbed and solution-phase superoxide and peroxide. Recently, we developed a rotating ring-disk technique incorporating a judiciously functionalized Au ring displaying remarkably high specificity toward solution-phase superoxide in neutral solutions which made it possible to detect such species generated by the reduction of dioxygen at a bare Au disk electrode as a function of the applied potential3. Our contribution illustrates the use of in situ differential reflectance spectroscopy to monitor the adsorption of hydroxyl ion on a Au rotating disk electrode during dioxygen reduction, as well as that of on line mass spectrometry under forced convection to measure the rates of heterogeneous peroxide disproportionation on the same electrode surface using a jet impinging electrolyte arrangement4. In basic solution, reduction of oxygen on Au electrodes is thought to proceed at least in part through a hydrogen peroxide intermediate. Many authors have speculated that subsequent disproportionation of the peroxide intermediate to oxygen and water plays an important mechanistic role, but measurements of disproportionation rates have not been attempted1, 2. This is most likely due to the difficulty of deconvoluting this reaction rate from the rates of oxygen / peroxide reduction. To this end, we measured both the consumption rate of peroxide using a rotating ring disk electrode (RRDE) and the production rate of oxygen by on-line mass spectrometry on a Au electrode at open circuit in 0.1 M NaOH. Shown in Figure 1 are plots of the partial pressure of dioxygen monitored with the mass spectrometer at two fixed disk potentials, i.e. 0.2 and -1.2 V, at which peroxide is oxidized and reduced respectively under diffusion limited conditions, yielding maximum and minimum O2 signal. The cell was then disconnected and the open circuit potential, after which the O2 signal settled at an intermediate value 1/3 of the way between that seen at 0.2 and -1.2 V. This spontaneous production of O2 from H2O2 without net current through the disk can only be explained by invoking H2O2 disproportionation. Furthermore, since only 1 O2 is produced per 2 H2O2 via disproportionation, the O2 signal at OCP represents consumption of 2/3 of the total H2O2 reaching the Au electrode. Fig. 1: A Au disk electrode surrounded by a porous, gas-permeable Teflon ring was mounted in the wall-jet configuration (flow rate 0.45 mL/s), and the O2 pressure passing through the Teflon ring was monitored by mass spec while the following electrochemical experiment was conducted: the Au electrode potential was held at either 0.2 (black) or -1.2 V vs Ag/AgCl (red) for 40 s, and then the circuit was opened. The solution was 0.1 M NaOH with 1 mM H2O2 (solid lines) or without H2O2 (dotted lines). The selected potentials of 0.2 and -1.2 V induce mass transport limited oxidation and reduction of H2O2, respectively, and so will yield the maximum and minimum O2 signal. Other authors have invoked superoxide as yet another intermediate in the reduction of oxygen on Au in alkaline solutions. Also to be discussed in this presentation is a theoretical analysis of the mechanism shown in Scheme I, which accounts for the contributions associated with all three species to the measured currents. References: Zurilla, R. W.; Sen, R. K.; Yeager, E. Electrochem Soc. 1978, 125, 1103-1109. Kim, J.; Gewirth, A. A. Phys. Chem. B. 2006, 110, 2565-2571. Feng, Z.; Georgescu, N. S.; Scherson, D. A. Chem. 2016, 88, 1088-1091. Treufeld, I.; Jebaraj, A. J. J.; Xu, J.; Martins de Godoi, D.; Scherson, D. A. Chem. 2012, 84, 5175-5179. Figure 1

Current development of advanced power electronics for electric vehicles demands high temperature, high energy density, and low loss polymer dielectrics. Multilayer films (MLFs), which are comprised of alternating high temperature/low loss linear dielectric polymer such as polysulfone (PSF) and high energy density polymer such as poly(vinylidene fluoride) (PVDF), are promising for this application, because high temperature tolerance, high energy density, and low loss can be achieved simultaneously. This study explored the reduction of impurity ion conduction loss in PSF/PVDF MLFs (e.g., the dissipation factor is as low as 0.003 at 1 Hz and 100 degrees C) without sacrificing high dielectric constant and high energy density. Various electric poling processes were explored at a temperature slightly below the glass transition temperature (T-g similar to 185 degrees C) of PSF. Compared with pure alternating current (AC) and pure direct current (DC) poling methods, unipolar (DC + AC) poling was found to be the most effective in polarizing impurity ions from the PVDF layers into the PSF layers. Because of the low segmental mobility below T-g, impurity ions were largely "locked" in PSF. The immobilization of impurity ions was thermally stable up to 120 degrees C. Because DC-link capacitors work with unipolar charge and discharge processes, these PSF/PVDF MLFs with low dielectric losses are promising for the application of advanced power electronics for the automobile industry.

Interfacial polarization due to space charges enhances electrical insulation and thus breakdown strength for multilayer polymer films.

In this report, a dipolar glass polymer, poly(2-(methylsulfonyl)ethyl methacrylate) (PMSEMA), was synthesized by free radical polymerization of the corresponding methacrylate monomer. Due to the large dipole moment (4.25 D) and small size of the side-chain sulfone groups, PMSEMA exhibited a strong γ transition at a temperature as low as -110 °C at 1 Hz, about 220 °C below its glass transition temperature around 109 °C. Because of this strong γ dipole relaxation, the glassy PMSEMA sample exhibited a high dielectric constant of 11.4 and a low dissipation factor (tan δ) of 0.02 at 25 °C and 1 Hz. From an electric displacement-electric field (D-E) loop study, PMSEMA demonstrated a high discharge energy density of 4.54 J/cm(3) at 283 MV/m, nearly 3 times that of an analogue polymer, poly(methyl methacrylate) (PMMA). However, the hysteresis loss was only 1/3-1/2 of that for PMMA. This study suggests that dipolar glass polymers with large dipole moments and small-sized dipolar side groups are promising candidates for high energy density and low loss dielectric applications.

ABSTRACT Three new isomeric diamines containing three, oxy‐linked benzonitriles (3BCN), one of which is asymmetric (meta, para, or m, p), are synthesized in a 3‐step sequence. Polycondensation of these diamines and four common dianhydrides (6FDA, OPDA, BTDA, and PMDA) in N,N ‐dimethylacetamide via poly(amic acid) precursors and thermal curing at temperatures up to 300 °C lead to three series of tough, creasable polyimide (PI) films (tensile moduli = 1.63 − 2.86 GPa). Among these PIs, two PMDA‐based PIs possess relatively high crystallinity and two OPDA‐based PIs, low crystallinity, whereas all 6FDA‐ and BTDA‐based PIs, and m,m ‐3BCN‐OPDA‐PI are amorphous, readily soluble in common polar aprotic solvents. Thermally stable and having high T g (216 − 341 °C), these PIs lose 5% weight around 493–503 °C in air and 463–492 °C in nitrogen. Dielectric properties have been evaluated by broadband dielectric spectroscopy (BDS) and electric displacement‐electric‐field (D‐E) loop measurements. D‐E loop results show an increase in high temperature permittivity (at 190 °C/1 kHz) from 2.9 (for parent PI CP2 with no nitrile group) to as high as 4.9 for these PIs, while keeping their dielectric loss relatively low. Thus, an increase in dipole moment density by the presence of three neighboring CN per repeat unit can increase the overall permittivity, which could be further enhanced by sub‐ T g mobility of para‐phenylene linkages (BDS results). Published 2014. J. Polym. Sci., Part A: Polym. Chem. 2014 J. Polym. Sci., Part A: Polym. Chem. 2015 , 53 , 422–436

A set of 12 new polyimides (PIs) with one or three polar CN dipoles directly attached to the aromatic diamine part were synthesized and their electric energy storage properties were studied using broadband dielectric spectroscopy (BDS) and electric displacement-electric field (D-E) loop measurements to determine their potential for high temperature film capacitors for aerospace applications. It was found that adding highly polar nitrile groups to the PI structure increased permittivity and thus electrical energy storage, especially at high temperatures, and 3 CN dipoles were better than 1 CN dipole. Below the glass transition temperature (T-g), a weak gamma transition was observed around -100 degrees C and a broad beta transition was observed between 100 and 150 degrees C. It was the beta (i.e., precursor dipolar motion before long-range segmental motion, or glass transition), rather than the gamma sub-T-g transition that substantially increased the permittivity of PIs. From the BDS results on PIs having 3 nitrile groups, the enhancement in permittivity from permanent dipoles decreased with dianhydride in the order of pyromellitic dianhydride (PMDA) > 4,4'-oxydiphthalic dianhydride (OPDA) >1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) > 4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Meanwhile, the increase in permittivity also decreased in the order of para-para, meta-para, and meta-meta linkage in the diamine, suggesting that the para-para linkage favored easier dipole rotation than the meta-meta linkage. From the D-E loop study, the PIs with a combination of PMDA dianhydride and a para-para linkage exhibited the highest discharged energy density and a reasonably low loss.

Two new diamines containing three nitriles are synthesized via a 3-step route. They are polymerized with four commercial dianhydrides (i.e. 6FDA, OPDA, BTDA and PMDA) in N,N -dimethylacetamide (DMAc) to afford poly(amic acid)s, which are thermally cured at temperatures up to 300 °C to form tough, creasable films. Most of these polyimides are soluble in common solvents. Their glass transition temperatures range from 216 to 341 °C. The polyimides are stable up to 400 °C. The dielectric constants of these OPDA-based polyimides increase from 2.9 (CP2) to 4.7 as measured by the D-E loops.

The authors have analyzed the content of about a dozen physical chemistry textbooks regarded as among the most commonly used by undergraduate educators in the U.S. to identify the extent and quality of the material therein covered in the specific area of physical electrochemistry. It is recommended that the textbook writers should take advantage of material treated in its most fundamental forms, and find means to extend it to modern technological applications. Examples would include extensions of the Debye Hückel theory of electrolytes to interfacial charging of ideal polarizable electrodes, a concept that relates directly to the operation of electrochemical double layer capacitors as energy storage devices found in container port cranes around the globe. Also long overdue is the use of lithium ion batteries as examples that should replace the Weston or Daniell's voltaic piles, as well as the broad introduction of proton exchange membrane electrolyte based fuel cells instead of their historical liquid based predecessors. The copious resources of material available on the Web should be also used.

A porous Teflon ring|solid disk electrode is herein described specifically designed for acquiring online mass spectrometric measurements under well-defined forced convection created by liquid emerging from a circular nozzle impinging on the disk under wall-jet conditions. Measurements were performed for the oxidation of hydrazine, N2H4, in a deaerated phosphate buffer electrolyte (pH 7) on Au, a process known to yield dinitrogen as the product. The N2+ ion currents, measured by the mass spectrometer, i(N2+), as well as the corresponding polarization curves recorded simultaneously displayed very similar s-like shapes when plotted as a function of the potential applied to the Au disk. In fact, the limiting currents observed both electrochemically and spectrometrically were found to be proportional to [N2H4]. However, the limiting values of i(N2+) did not increase monotonically with the flow rate, νf, reaching instead a maximum and then decreasing to values independent of νf. This behavior has been attributed in part to hindrances in the mass transport of gases through the porous materials.