The state-of-the-art of polymer electrolyte membrane fuel cell (PEMFC) technology is based on perfluorosulfonic acid (PFSA) polymer membranes operating at a typical temperature of 80 °C. Some of the key issues and shortcomings of the PFSA-based PEMFC technology are briefly discussed. These include water management, CO poisoning, hydrogen, reformate and methanol as fuels, cooling, and heat recovery. As a means to solve these shortcomings, high-temperature polymer electrolyte membranes for operation above 100 °C are under active development. This treatise is devoted to a review of the area encompassing modified PFSA membranes, alternative sulfonated polymer and their composite membranes, and acid−base complex membranes. PFSA membranes have been modified by swelling with nonvolatile solvents and preparing composites with hydrophilic oxides and solid proton conductors. DMFC and H2/O2(air) cells based on modified PFSA membranes have been successfully operated at temperatures up to 120 °C under ambient pressure...

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Approaches and Recent Development of Polymer Electrolyte Membranes for Fuel Cells Operating above 100 °C

https://www.fkit.unizg.hr/_download/repository/Smart_Windows-_Review.pdf

Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review

A comprehensive overview is presented on the implication of silica-based organic-inorganic hybrid materials in electrochemical science. It involves composite materials of both class I (weak bonds between the organic and inorganic components) and class II (strong chemical bonds). Starting with a description of the common designs of electrodes modified with these hybrids, the review then reports their applications in the various fields of electrochemistry, illustrating the diversity of the organically modified silicates used for this purpose. The mild chemical conditions allowed by the sol-gel process provide very versatile access to these electrochemical devices. They have found many applications in electroanalysis, including preconcentration associated with voltammetric detection, permselective coatings, electrochemical sensors, electrocatalysis, and detectors for chromatography. They were also applied as redox and conducting polymers, as solid polymer electrolytes for batteries, for the design of spectroelectrochemical and electro-chemiluminescence devices, and in the field of electrochemical biosensors.

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Electrochemical Applications of Silica-Based Organic−Inorganic Hybrid Materials

Progress in the area of proton conducting polymer electrolyte membranes is intimately linked with the development of polymer electrolyte membrane fuel cells, and is today largely driven by the insufficient properties of humidified Nafion® membranes at temperatures above 100 °C. Recent developments in the field include new ionomers and hybrid membranes containing inorganic nanoparticles to control morphology and enhance water retention, as well as improved systems based on the complexation of basic polymers with oxo-acids. In addition, the molecular design and synthesis of completely new all-polymeric electrolytes that rely entirely on structure diffusion of the protons holds great promise in the long perspective.

Recent developments in high-temperature proton conducting polymer electrolyte membranes

The implications of organically-modified silica-based materials in electrochemical science is reviewed along with some selected recent trends in the field of functionalized and sol–gel silica electrochemistry. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the preparation and applications of sol–gel derived composite (carbon, gold, nanotubes) electrodes, the electrochemical characterisation of mass transfer reactions in porous functionalized silicas, solid-state electrochemistry and gas sensors involving sol–gel materials, imprinted functionalized silica, and the electrochemical characterisation and applications of ordered mesoporous organosilicas.

Exciting new directions in the intersection of functionalized sol–gel materials with electrochemistry

Proton-conducting sol-gel hybrids containing heteropoly acids

Hybrid organic−inorganic proton conducting gels (PWA/ICS−PPG or SiWA/ICS−PPG) were made from 3-isocyanatopropyltriethoxysilane and poly(propylene glycol)bis(2-aminopropyl ether), resulting in a hybrid silicon precursor (ICS−PPG) in which was dispersed phosphotungstic acid (PWA) or silicotungstic acid (SiWA) in ethanol. In this system, heteropoly acid takes on the additional role of catalyst, initiating the hydrolysis/condensation reactions of the sol−gel composite. The existence of amidonium ions [C(OH)NH+] was established from the IR and Raman spectra of PWA/ and SiWA/ICS−PPG composites below and close to the crystallization limits (70−75%). The crystallization of the Keggin ions inside the ICS−PPG host was determined from the XRD spectra of the composites and confirmed also using vibrational spectroscopy, which shows the appearance of H3O+ modes at 1700−1710 cm-1. The amidonium ions help in the immobilization of the negatively charged Keggin ions in the membranes, ensuring their uniform distribution in ...

Structure of and interactions between P/SiWA Keggin nanocrystals dispersed in an organically modified electrolyte membrane

The behavior of sol-gel prepared thin films exhibiting a gasochromic effect; ie, a reversibly change in colour from transparent when in air to blue when in H2, has been studied The films were prepared from a Pd (PdCl2) doped peroxopolytungstic acid sol using a dip-coating technique Transmission electron microscopy together with selected area electron diffractrometry revealed that the films consist of monoclinic and hexagonal nanocrystalline grains (∼2–5 nm) embedded in an amorphous phase This amorphous hydrated phase was established using Infrared (IR) and Raman spectroscopy Characteristic vibrations observed in the in-situ IR spectra of the coloured and bleached states revealed the presence and the importance of terminal W=O and W—OH2 groups in the colouring of the films Colouring/bleaching changes of Pd doped W-PTA films observed using in-situ UV-Vis spectroscopy are described in terms of Pd concentration, and the number of reducing/oxidising cycles The rate of colouring/bleaching is greater for films containing a higher concentration of Pd but the change in the optical density does not increase, ie, shows saturation

Gasochromic Behavior of Sol-Gel Derived Pd Doped Peroxopolytungstic Acid (W-PTA) Nano-Composite Films

We studied the gasochromic effect of amorphous peroxopolytungstic acid (W-PTA), W-PTA (ormosil) and crystalline WO3 films. These latter films were prepared after a heat treatment of W-PTA/ormosil films at 450°C. The ormosil served as a template, providing the monoclinic WO3 films with adequate porosity. The spill-over effect was attained by impregnating the porous WO3 crystalline films with H2PtCl6 followed by a heat treatment at 380°C. The amorphous films became gasochromic with the addition of PdCl2 to the corresponding W-PTA and W-PTA/ormosil sols. Structural features of all the films were studied with the help of infrared (IR) spectroscopy and transmission electron microscopy (TEM). In situ IR spectra of the films, performed in the presence of reducing (H2/Ar) and oxidising (O2/Ar) gases, revealed a reversible transformation of the monoclinic to the tetragonal H
 x
 WO3 phase. At the same time the coloration (reduction) of the amorphous films was accompanied by the formation of coordinated water molecules and increased numbers of W=O bonds. Gasochromic colouring/bleaching changes and the corresponding kinetics were assessed from in situ UV-visible transmission measurements on the films.

N. Grošelj

Papers

Proton-conducting sol-gel hybrids containing heteropoly acids

Structure of and interactions between P/SiWA Keggin nanocrystals dispersed in an organically modified electrolyte membrane

Gasochromic Behavior of Sol-Gel Derived Pd Doped Peroxopolytungstic Acid (W-PTA) Nano-Composite Films

IR Spectroscopic investigations of gasochromic and electrochromic sol-gel-derived peroxotungstic acid/ormosil composite and crystalline WO3 films

Electrical and IR spectroscopic studies of peroxopolytungstic acid/organic–inorganic hybrid gels