ABSTRACT
Anion exchange membrane fuel cells (AEMFCs) have recently attracted significant attention as low-cost alternative fuel cells to traditional proton exchange membrane fuel cells because of the possible use of platinum-group metal-free electrocatalysts. Over the past decade, new materials dedicated to the alkaline medium, such as anion exchange membranes (AEMs) and anion exchange ionomers (AEIs), have been developed and studied in AEMFCs. However, only a few AEMs and AEIs are commercially available, and there are no ready-to-use membrane electrodes assemblies (MEAs) with the desired AEMs and AEIs. Consequently, the need to manufacture in-house CCMs or GDEs becomes a reality that we must face. This work deals with the influence of ionomer content on the prepared MEAs with the commercial anion exchange membrane and ionomer from Aemion™ Ionomr Innovations AF1-HNN8-2 and AP1-ENN8/HNN8 respectively and by varying the support (gas diffusion layer or membrane). The prepared MEAs were characterized morphologically by SEM and profilometry, as well as electrochemically by AEMFC polarization curves and cyclic voltammetry. In addition, an attempt to investigate water management was made with and without a reference electrode in the cell to understand the behavior of water in an operating AEMFC. Our results show that CCM-based MEAs can undergo deformation during the anion conversion step, leading to weakening of the membrane and hence faster degradation in the fuel cell. On the contrary, no deformation was observed for the GDEs during the anionic conversion, although the results are poorer due to (i) poor interface contact between membrane and GDE that depends on ionomer ratio in the ink and (ii) a high overpotential at the anode due to the production of water that cannot be effectively evacuated.
ABSTRACT
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
Ce-doped ZnO (ZnO:Ce) nanorods have been prepared through a solvothermal method and the effects of Ce-doping on the structural, optical and electronic properties of ZnO rods were studied. ZnO:Ce rods were characterized by XRD, SEM, TEM, XPS, BET, DRS and Raman spectroscopy. 5% Ce-doped ZnO rods with an average length of 130 nm and a diameter of 23 nm exhibit the highest photocatalytic activity for the degradation of the Orange II dye under solar light irradiation. The high photocatalytic activity is ascribed to the substantially enhanced light absorption in the visible region, to the high surface area of ZnO:Ce rods and to the effective electron-hole pair separation originating from Ce doping. The influence of various experimental parameters like the pH, the presence of salts and of organic compounds was investigated and no marked detrimental effect on the photocatalytic activity was observed. Finally, recyclability experiments demonstrate that ZnO:Ce rods are a stable solar-light photocatalyst.
