Search

As programs to support efficient and sustainable energy sources are expanding, research into the potential applications of the hydrogen vector is accelerating. Proton exchange membrane fuel cells are electrochemical converters that transform the chemical energy of hydrogen into electrical energy. These devices are used today for low- and medium-power stationary applications and for mobility, in trains, cars, bicycles, etc. Proton exchange membrane fuel cells use a polymer membrane as the electrolyte. The role of the membrane is multiple: it must separate gases, be an electronic insulator and a very good ionic conductor. In addition, it must resist free-radical chemical attack and have good mechanical strength. Nafion-type perfluorinated membranes have all these properties: the fluorinated backbone is naturally hydrophobic, but the hydrophilic ionic groups give the material excellent water sorption properties. The water adsorbed in the structure is extremely mobile, acting as a transport medium for the protons generated at the anode. Although it has been studied for a long time and has been the subject of a large number of papers perfluorinated membranes are still the reference membranes today. This article reviews some contributions of Nuclear Magnetic Resonance methods in liquid state to the study of water properties in the structure of Nafion-type perfluorinated membranes.

The fabrication step of the catalyst layer (CL) is important to master in order to achieve good performance in fuel cells. Nevertheless, the final structure of a CL depends on many factors, such as the ink composition and preparation, as well as the order of its preparation steps. However, it is not easy for neophytes to understand the relationship between the composition of the ink with the obtained structure of the catalyst layer and its performance in fuel cells. In this work, a systemic experimental study was carried out in order to qualitatively correlate the performance of the PEMFC with the structure of the catalyst layer by playing on different parameters such as the composition and preparation of the ink and the operating conditions. All of the prepared samples were characterized by electron microscopy and profilometry, as well as by electrochemical tests at a single-cell level. The main results show that (i) the chosen ratio and ingredients result in a catalyst layer structure that can affect the PEMFC performance in different ways, and (ii) the reproducibility of the results requires particular care in the choice of catalyst and carbon support. [ABSTRACT FROM AUTHOR]

Abstract: The quality of Al2O3–TiO2 mixed oxides produced in continuous mode by using two original rapid mixers (impinging jets and sliding surface mixing devices) as precipitation reactors are compared with those obtained by a standard stirred tank. The properties of agglomerate particles strongly depend on the operating conditions and particularly on the type of precipitator used for their production. [Copyright &y& Elsevier]

A proton-exchange membrane fuel cell (PEMFC) constitutes today one of the preferred technologies to promote hydrogen-based alternative energies. However, the large-scale deployment of PEMFCs is still hampered by insufficient durability and reliability. In particular, the degradation of the polyelectrolyte membrane, caused by harsh mechanical and chemical stresses experienced during fuel cell operation, has been identified as one of the main factors restricting the PEMFC lifetime. An innovative chemical-mechanical ex situ aging device was developed to simultaneously expose the membrane to mechanical fatigue and an oxidizing environment (i.e., free radicals) in order to reproduce conditions close to those encountered in fuel cell systems. A cyclic compressive stress of 5 or 10 MPa was applied during several hours while a degrading solution (H2O2 or a Fenton solution) was circulated in contact with the membrane. The results demonstrated that both composite Nafion™ XL and non-reinforced Nafion™ NR211 membranes are significantly degraded by the conjoint mechanical and chemical stress exposure. The fluoride emission rate (FER) was generally slightly lower with XL than with NR211, which could be attributed to the degradation mitigation strategies developed for composite XL, except when the pressure level or the aging duration were increased, suggesting a limitation of the improved durability of XL. [ABSTRACT FROM AUTHOR]