Perfluorosulfonyl Imide versus Perfluorosulfonic Acid Ionomers in Proton-Exchange Membrane Fuel Cells at Low Relative Humidity.

Designing highly conductive ionomers at high temperature and low relative humidity is challenging in proton-exchange membrane fuel cells. Perfluorosulfonyl imide ionomers were believed to achieve this goal, owing to their exceptional acidity and excellent thermal stability. Perfluorosulfonyl imide ionomers are less conductive than the analogous perfluorosulfonic acids despite similar membrane microstructure. In this study, the distinct behavior is rationalized by in situ synchrotron infrared spectroscopy during hydration. The protonation mechanism, formation of the protonic moiety and water clustering are totally different for the two different families of membranes. The ionization mediated by trans-to-cis conformational transition of the perfluorosulfonyl imide ionomer is not accompanied by the formation of hydronium ions. In contrast, Zundel-ion entities were identified as the elementary protonic complex, which is stable over the hydration range. The H-bond network of surrounding water molecules appears to be less connected and the protons remain highly localized and unavailable for efficient structural transport. The delocalization of protons and their mitigated interaction with the surrounding medium are prominent effects that negatively impact conductivity.

Durability of Polymer Metal Multilayer: Focus on the Adhesive Chemical Degradation.

Mechanical toughness and high barriers to air and water may be combined in a polymer-metal multilayer film, provided that the two materials are properly bonded together. Delamination is indeed the most severe flaw observed in service. This suggests that the polyurethane (PU) adhesive at the polymer-metal interface fails to bear the shear forces, as happens principally if a multilayer system is submitted to elevated temperature and humidity. A Raman microscopy of the multilayer revealed a cohesive delamination, with glue on both the surfaces. A detailed investigation of the kinetic of degradation of the polyester was therefore carried out. IR spectroscopy of the standalone PU film hydrolyzed in a controlled manner furnished a series of aging markers. The reference curve was established for approximately a year in continuous severe aging conditions. This curve could be further used to compare the amount of degradation in real systems in a wide range of conditions and time. Moreover, at the metallized interphase, a complex with a free hydroxyl group was detected. The content of this AlIII complex based on terephthalate or carbamate increases with the progress of the ester hydrolysis reactionin the layer.

Mechanical Reliability of Flexible Encapsulated Organic Solar Cells: Characterization and Improvement.

The encapsulation of organic photovoltaic (OPV) devices can help mitigate the degradation induced by environmental factors like water and oxygen and thus potential to increase OPV lifetime. Because flexibility is an important parameter for targeted OPV applications, this paper proposes a fundamental study on the impact of the roll-to-roll flexible encapsulation process. Both performance and mechanical reliability of encapsulated devices have been scouted. Furthermore, it has been demonstrated that a relatively simple peeling technique allows understanding the role of the interfaces inside a multilayered OPV device supported by a flexible poly(ethylene terephthalate) substrate. For this purpose, the peeling strengths between each layer were measured using a series of partial devices. This provided a quantitative analysis of the mechanical strength or quality of each interface. Two interfaces revealed pronounced weaknesses: active layer with hole transporting layer and transparent conducting electrode with electron transporting layer. Among various surface treatments applied to improve these interfaces, an optimized UV-ozone (UVO3) treatment proved to modify substantially the surface properties of used zinc oxide (ZnO) and thus improved its adhesion to the neighboring layers. The physicochemical and structural changes of ZnO have been confirmed by IR spectroscopy and contact angle measurements. It has also been shown that better interfaces within the device improve the overall performance of the devices and their resilience to roll-to-roll encapsulation.

Water Vapor Sorption Properties of Polyethylene Terephthalate over a Wide Range of Humidity and Temperature.

The dynamic and equilibrium water vapor sorption properties of amorphous polyethylene terephthalate were determined via gravimetric analysis over a wide range of temperatures (23-70 °C) and humidities (0-90% RH). At low temperature and relative humidity, the dynamics of the sorption process was Fickian. Increasing the temperature or relative humidity induced a distinct up-swing effect, which was associated with a plasticization/clustering phenomenon. For high temperatures and relative humidity, a densification of the polymer was evidenced. In addition to the classical Fickian diffusion, a new parameter was introduced to express the structural modifications of PET. Finally, two partial pressures were defined as thresholds that control the transition between these three phases. A simplified state diagram was finally proposed. In addition, the thermal dependence of these sorption modes was also determined and reported. The enthalpy of Henry's water sorption and the activation energy of diffusion were independent of vapor pressure and followed an Arrhenius law.