The present study examines the ionic conductivity and transport properties for ionic liquids confined within mesoporous materials. The fragility index was determined for several samples with varying microstructures and used to characterize performance as a pseudosolid electrolyte. The degree of microstructure complexity was characterized via the mass fractal dimension, which correlates with the fragility index in the pore size domain studied. We demonstrate for the materials studied here that the presence of the microporous matrix serves to inhibit ion mobility, and as the complexity of the matrix increases, the fragility index also increases, leading to lower conductivity materials. The microstructural features influencing conductivity were examined using Archie’s law when assuming the matrix conductivity to be negligible. This type of analysis, previously validated for rock matrices, has now been extended to pseudosolid electrolyte materials. The results indicate that ionogel samples can approach the conductivity of the unconfined ionic liquid. These conclusions are applicable to a variety of pseudosolid electrolyte systems and have important implications for the design of electrochemical devices.

This paper reports and analyzes, for the first time, the effective Young's modulus and hardness of nanoparticle-based silica aerogels and xerogels with porosity ranging from 46 to 81%. Pure silica aerogel and xerogel monoliths were synthesized by (i) gelation of aqueous suspensions of silica nanoparticles on omniphobic sub-strates (PTFE or perfluorocarbon liquids), (ii) aging, (iii) drying at ambient temperature and pressure, and (iv) calcination. The aging and calcination conditions were varied to elucidate their effect on the mechanical properties of the monoliths. Both the effective Young's modulus and the hardness of the mesoporous slabs were measured by nanoindentation and were found to obey a power law as a function of the effective density. No effect of the synthetic conditions or structural parameters other than porosity were observed. Interestingly, the effective hardness was linearly proportional to the effective Young's modulus. The elastic properties of the present nanoparticle-based materials were compared with those of the molecular precursor-based silica aerogels and xerogels reported in the literature. A single relationship was proposed that can be used to estimate the effective Young's modulus of nanoparticle-based and molecular precursor-based silica aerogels and xerogels with porosity between 0 and 98% and Young's modulus between similar to 10(-4) and 70 GPa. Deposition of an alumina coating was also demonstrated as a way to increase the hardness of these mesoporous monoliths by a factor 2-13 for porosity of 40-73%. The experimental results and the accompanying analysis broaden the understanding of structure-property relationships in mesoporous silica and will help in the design and fabrication of mesoporous silica components.

Dielectric materials have been used for decades for energy applications where their insulation and polarizability properties are critical. In the energy storage field, most material scientists envision high-k dielectric layers in contact with an active material only as an insulating passivation layer. In microelectronics, this concept has been modified with the study of dielectrics at nanoscale level revealing interesting properties scarcely known by other fields. We propose to reconsider the vision of high-k dielectric materials for energy at nanoscale specifically. Based on microelectronic measurement techniques and nanometric control of dielectric thickness by Atomic Layer Deposition (ALD), an ultra-thin pinhole-free alumina (Al2O3) layer on a silicon nanowire (SiNW) is shown to display thickness dependent tunneling electrical conduction. This result brings a new light on this material class in the energy field and allows original approaches toward achieving scientific leaps. As an illustrative application, a silicon based micro-supercapacitor (MSC) protected by 3 nm of alumina dielectric layer exhibits Electrical Double Layer Capacitance (EDLC) by means of tunneling current in aqueous electrolyte, an unprecedented result for this material, with outstanding lifetime capacity retaining 99% of its initial capacitance after 2 million cycles. Extended to multiple energy materials, such method could lead to notable progress. (C) 2021 Elsevier Ltd. All rights reserved.

Composite porous supercapacitor electrodes were prepared by growing poly(3,4-ethylenedioxythiophene) (PEDOT) on graphite nanoplatelet- or graphene nanoplatelet-deposited open-cell polyurethane (PU) sponges via a vapor phase polymerization (VPP) method. The resulting composite supercapacitor electrodes exhibited great capacitive performance, with PEDOT acting as both the conductive binder and the active material. The chemical composition was characterized by Raman spectroscopy and the surface morphology was characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV), charge-discharge (CD) tests and electrochemical impedance spectroscopy were utilized to study the electrical performance of the composite electrodes produced in symmetrically configured supercapacitor cells. The carbon material deposited on PU substrates and the polymerization temperature of PEDOT affected significantly the PEDOT morphology and the electrical properties of the resulting composite sponges. The highest areal specific capacitance 798.2 mF cm−2 was obtained with the composite sponge fabricated by VPP of PEDOT at 110 °C with graphene nanoplatelet-deposited PU sponge substrate. The capacitance retention of this composite electrode was 101.0% after 10,000 charging–discharging cycles. The high flexibility, high areal specific capacitance, excellent long-term cycling stability and low cost make these composite sponges promising electrode materials for supercapacitors.

Vapor-phase polymerized poly(3,4-ethylenedioxythiophene) (PEDOT)/TiO2 composite fibers were fabricated and applied as the supercapacitor electrode materials. TiO2 fibers were prepared as substrates for the vapor-phase polymerization process, by electrospinning and calcination in air. The symmetric supercapacitor cells assembled with the resulting composites were studied by a series of electrical measurements including cyclic voltammetry, charge-discharge characterization and electrochemical impedance spectroscopy. To further understand the capacitive behavior, the band gap energy of the composite fibers and the specific surface area of TiO2 fibers calcined at varied temperatures were measured. The highest specific capacitance of PEDOT on TiO2 fibers to date, 87.9 Fg(-1), was achieved with the composite fibers prepared by vapor-phase polymerization at 50 degrees C on the TiO2 fibers calcined at 550 degrees C. The pseudocapacitance and the reversibility of PEDOT were improved in comparison to other PEDOT/TiO2 binary composites. (C) 2016 Elsevier Ltd. All rights reserved.