Strategies for impure hydrogen use in polymer electrolyte fuel cell systems

Availability of high purity H2 for low temperature polymer electrolyte fuel cell (PEFC) technology is a necessity for optimum performance and durability. H2 purity depends on the production process as well as post purification measures, which may increase the final pump outlet cost of H2 fuel and operating cost of PEFC applications. Low cost H2 is produced in refineries and other reforming processes. Presence of certain contaminants such as methane, carbon dioxide and carbon monoxide in this H2 may however cause performance degradation in fuel cells. The aim of this thesis is to investigate strategies to mitigate and overcome the fuel cell performance losses resulting from the use of impure H2. Firstly, stack level testing on H2 with isolated contaminants of known concentration are conducted to assess performance losses. These studies are expanded in a single cell for comparison with stack results as well as in devising strategic mitigation techniques. CO, being a major contaminant, is extensively studied with variation of operating current density and CO concentration. Performance losses are partially rectified through application of a CO tolerant electrocatalyst, Pt-Ru/C instead of Pt/C. Two more techniques of air-bleeding and pulsed oxidation are also investigated alongside Pt-Ru/C electrocatalyst for performance recovery through CO oxidation. Parametric studies of pulsed oxidation are undertaken with 80 ppm CO containing H2 fuel for performance recovery and energy efficiency comparison with respect to pure H2 efficiencies. Up to 95% recovery in performance is observed at 0.5 A cm-2 with strategic application of pulsed oxidation when using a threshold cell potential for activation. These studies are further extended to long term pulsing operation of up to 4000 cycles to gauge the robustness and effectiveness of the pulsing process. These studies demonstrate cell potential recovery over extended pulse cycles without any significant decay of fuel cell performance through monitoring of droptime and peak potential values. Lastly, a zero-dimensional model is developed to study the transient surface coverage of different species present at the anode during CO poisoning and predict cell potential losses. It is extended to cover the pulsed oxidation effect and provide overall efficiency of the fuel cell with change of anodic flow parameters. The cost effectiveness of pure and impure H2 fuel used with mitigation techniques are compared and discussed for the interest of commercialization of such processes for the practical use of impure H2 in PEFC systems

'Only connect': researchers and teachers in dialogue

This article responds to recent critiques of the usefulness of research findings to teaching, and the call for teachers to rely on their experiences and intuition. I discuss the fallibility of intuition and then examine the nature of research and of critical thinking and their importance for teachers and teacher education. I provide evidence of how research has been able to broaden and deepen our understanding of teaching and learning in ways that can be applied to both the classroom and to language teaching materials. I end by exploring the ways in which researchers and teachers in the area of second language teaching can continue to support each other: on initial teacher education programmes; through the materials made available to teachers; throughout continuing professional development; and through teacher research. Most importantly, I stress the value of maintaining a two-way dialogue between EFL teachers and researchers

Modéliser pour mieux gérer l'eau selon les besoins des hommes et des écosystèmes

National audienceLes enjeux liés à la ressource en eau sont de plus en plus présents et pressants. Les activités anthropiques dans un contexte de changement climatique représentent une lourde menace tant pour les écosystèmes aquatiques que pour les hommes eux-mêmes. La directive européenne sur l'eau (DCE) propose un cadre de travail global qu'il convient d'articuler en cohérence avec les enjeux nationaux, régionaux et locaux afin de mieux gérer la ressource selon les besoins des hommes et des écosystèmes

The low-velocity impact response of thin, stiffened CFRP panels.

An extensive study of into the static loading response and low-velocity impact response of plain and stiffened CFRP panels was conducted. The study investigated the impact response of the CFRP panels over a range of impact energies that include incident kinetic energies sufficiently high to cause complete penetration of the panel by the impacting mass. Static tests were also conducted by driving a hemispherical-nosed indentor into the panel up to displacements that resulted in the complete penetration of the panel by the indentor. Results from these tests suggest that the static perforation energy could predict the impact perforation energy with reasonable accuracy. A lumped-parameter mass-spring-damper model that attempted to incorporate the effects of material damage to the panel response was developed. The model was found to be sufficiently accurate in predicting the response of thin panels to static and impact loads up to the critical delamination force threshold. Assessment of the damaged panels through Penetrant-Enhanced X-Ray methods led to the identification of damage transition energy thresholds that differentiate between changes in damage mechanism. The damage transition energy thresholds were found to be constant fractions of the impact perforation energy