Dielectric capacitors with a high operating temperature applied in electric vehicles, aerospace and underground exploration require dielectric materials with high temperature resistance and high energy density. 

High-temperature polyimide dielectric materials for energy storage: theory, design, preparation and properties

Nanoparticle (NP)/polymer nanocomposites received considerable attention because of their important applications including catalysis. Metal and metal oxide NPs may impart catalytic properties to polymer nanocomposites, while polymers with a different structure, functionality, and architecture control the NP formation (size, shape, location, composition, etc.) and in this way, govern catalytic properties of nanocomposites. In this review we will discuss the influence of the polymer nanostructure (thin or grafted layers, polymer ordering, polymer nanopores), architecture (branched vs linear), functional groups (coordinating or ionic), specific properties (reducing, stimuli responsive, conductive), etc. on the formation of metal or metal oxide NPs and the catalytic behavior of the nanocomposites. The development of novel and efficient catalysts is crucial for progress in chemical sciences, and this explains a huge number of publications in this area in recent years. Taking into consideration previous review articles on NP/polymer catalysts, we limited this review to a discussion of a narrow temporal scope (2017-April 2019), while embracing a broad subject scope, i.e., considering any polymers and NPs which form catalytic nanocomposites. This gives us a unique view of the field of catalytic polymer nanocomposites and allows understanding of where the field is going.

Role of Polymer Structures in Catalysis by Transition Metal and Metal Oxide Nanoparticle Composites.

Catalytic selectivity in the epoxidation of ethylene to form ethylene oxide on alumina-supported silver catalysts is dependent on the geometric structure of catalytically active Ag particles and reaction conditions. Shape and size controlled synthesis of Ag nanoparticles is used to show that silver nanocubes exhibit higher selectivity than nanowires and nanospheres. For a given shape, larger particles offer improved selectivity. The enhanced selectivity toward ethylene oxide is attributed to the nature of the exposed Ag surface facets; Ag nanocubes and nanowires are dominated by (100) surface facet and Ag nanospheres are dominated by (111). Furthermore, the concentration of undercoordinated surface sites is related to diminished selectivity to ethylene oxide. We demonstrate that a simple model can account for the impact of chemical and physical factors on the reaction selectivity. These observations have also been used to design a selective catalyst for the ethylene epoxidation reaction.

Shape- and size-specific chemistry of Ag nanostructures in catalytic ethylene epoxidation

The availability of high-temperature dielectrics is key to develop advanced electronics and power systems that operate under extreme environmental conditions. In the past few years, many improvements have been made and many exciting developments have taken place. However, currently available candidate materials and methods still do not meet the applicable standards. Polyimide (PI) was found to be the preferred choice for high-temperature dielectric films development due to its thermal stability, dielectric properties, and flexibility. However, it has disadvantages such as a relatively low dielectric permittivity. This chapter presents an overview of recent progress on PI dielectric materials for high-temperature capacitive energy storage applications. In this way, a new molecular design of the skeleton structure of PI should be performed to balance size and thermal stability and to optimize energy storage property for high-temperature application. The improved performance can be generated via incorporation of inorganic units into polymers to form organic-inorganic hybrid and composite structures

/pdf/high-temperature-polyimide-dielectric-materials-for-energy-3c9f9v58vl.pdf

High-temperature polyimide dielectric materials for energy storage

Polyimide (PI) films with extremely high breakdown strength (451 kV/mm), energy density (5.2 J/cm3), and discharge efficiency (86.7%) at the room temperature are fabricated by simple solution casting method. Barium titanate (BaTiO3) nanoparticles are introduced into PI matrix, giving rise to enhanced dielectric permittivity (6.8) and low dielectric loss (0.012). Dielectric and energy storage performances of the BTO/PI nanocomposites are thoroughly investigated up to 200 °C. The breakdown strengths of both pure PI and BTO/PI nanocomposites decrease dramatically with the increase in the temperature, owing to the low thermal conductivity of PI and the consequent thermal runaway caused by the accumulation of Joule heat under high electric field. Despite of the enhanced electric displacement, BTO/PI nanocomposites exhibit low discharge energy density due to the substantially compromised breakdown strength induced by the BTO nanoparticles.

Dielectric and energy storage performances of polyimide/BaTiO 3 nanocomposites at elevated temperatures

Water-soluble silver nanoparticles stabilized by poly(amic acid) salt (Ag–PAAS) were synthesized by a one-pot method and were characterized by using UV-vis absorption, transmission electron microscopy, powder X-ray diffraction, and ζ potential measurements. The Ag–PAAS catalyzed selective hydration of nitriles to amides in water allowed for not only highly efficient quasi-homogeneous catalytic reactions under mild conditions, but also an easy recovery and reuse of the catalyst attributed to the pH response of the PAAS.

Poly(amic acid) salt-stabilized silver nanoparticles as efficient and recyclable quasi-homogeneous catalysts for the aqueous hydration of nitriles to amides

High dielectric permittivity materials are much desirable in the electric industry. Filling polymer matrix with conductive powders to form percolative composites is one of the most promising methods to achieve high dielectric permittivity. However, they do not always provide high mechanical properties and thermal stability, which seriously limit their applications. In this study, we present the preparation of functional core–shell structured silver nanowires/polyimide (AgNWs/PI) hybrid film with high dielectric permittivity and low loss dielectric. The core–shell structure of AgNWs was characterized by transmission electric microscopy. The dynamical mechanical analysis showed that AgNWs/PI hybrid films had relative high dynamic mechanical properties with storage modules over 1 Gpa. Moreover, the hybrid films exhibited excellent thermal stability with 5 % weight-loss temperature above 500 °C. The dielectric properties of the carbon-coated AgNWs hybrid films were remarkably improved. The maximum dielectric permittivity of hybrid films is 126 at 102 Hz, which was 39 times higher than that of pure PI matrix, while the dielectric loss of that is still remained at a low value. This study showed a new method to improve the dielectric, dynamic mechanical and thermal properties of films.

High dielectric, dynamic mechanical and thermal properties of polyimide composite film filled with carbon-coated silver nanowires

Poly(amic acid) salt-mediated palladium and platinum nanoparticles as highly active and recyclable catalysts for hydrogenation of nitroarenes in water under ambient conditions

Graphite oxide (GO) was prepared by the pressurized oxidation method and incorporated into polyimide (PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 102 Hz and was 26 times that of the pure PI.

Enhanced dielectric permittivity of graphite oxide/polyimide composite films

A simple and efficient method for in situ preparation of highly stable polyimide (PI)-supported silver nanoparticles (AgNPs) was proposed. This process achieves excellent dispersion and high stability of AgNPs in the PI matrix. The formation of AgNPs in PI and the morphology evolution of PI/Ag nanocomposites were characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and x-ray photoelectron spectra studies. The catalytic properties of these PI-supported AgNPs were investigated by monitoring the reduction of 4-nitrophenol by excess NaBH4 in water. The catalytic reaction was observed to have a pseudo first-order rate constant of 0.567 min−1 (9.45 × 10−3 s−1), which is comparable to other heterogeneous silver catalysts reported in the literature. Notably, the PI-supported AgNPs retained their relatively high catalytic activity over seven recycles with almost no leaching of catalytic species in the reaction solution. Moreover, the catalytic activity of the catalyst is still quite appreciable even after a six-month shelf-storage under room temperature.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291415002587

A highly robust and reusable polyimide-supported nanosilver catalyst for the reduction of 4-nitrophenol

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