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

L'Acteur en 4 Dimensions pour une exploration sociale et patrimoniale du jeu d'acteurs territorial

International audienceUne négociation plus écologique associée à une conservation plus humaine, telle est la piste à suivre pour tendre vers l'idée d'un développement durable socio-centré et d'une nouvelle gouvernance environnementale (voir chapitre 3). Reste à élaborer des méthodologies innovantes qui viseraient à prendre en compte acteurs forts, faibles et absents au sein de projets territoriaux, afin d'" éclairer " cette nouvelle gouvernance. Notre proposition : l'Acteur en 4 Dimensions (A4D). Ce modèle d'analyse du jeu d'acteurs permet d'analyser les interactions acteur/complexe multi-acteurs et acteurs/territoire et d'en fournir des représentations à l'aide d'une approche transdisciplinaire [SEB 03]. Basé sur des concepts issus principalement de la sociologie, de l'anthropologie, de la géographie et de la psychologie environnementale, notre prototype propose une radiographie, une algorithmisation des acteurs et permet de qualifier les groupes de façon neutre, à travers ce que nous appelons l'empreinte territoriale. Ce spectre graphique fabrique des types abstraits purement descriptifs en décrivant la posture d'un groupe vis-à-vis des autres (rapport social) et de l'environnement (rapport patrimonial). Cet outil miroir renvoie un cadre où vont se situer les acteurs. L'A4D, mobilisé dans une négociation territoriale, se doit de proposer un cadre collectif, par empilement des empreintes territoriales, pour répondre à la question suivante : qu'est-ce qu'un fonctionnement collectif (les acteurs étant considérés en tant que groupes constitués) laisse de côté

Exploring the Relationship Between Course Structures and Student Motivation in Introductory College Calculus: A Self-Determination Theory Perspective

Calculus I occupies a gatekeeper role for STEM majors nationwide. The Mathematical Association of America (MAA) investigated this issue and found that the use of active learning strategies was one important characteristic of successful calculus programs across the country. This sequential explanatory mixed-methods study explores this issue further by examining the relationship between student motivation and course structures for introductory calculus. Calculus I course structures with differing levels of active learning were examined. The theoretical framework of self-determination theory (SDT) guided this study, which defines three basic psychological needs that are essential to fostering students’ motivation: competence, autonomy, and relatedness. The quantitative phase of this study consisted of analysis of student survey data to investigate the difference in students’ perceptions of these motivational components between the three course types (traditional lecture, large active learning, and hybrid online). The findings showed that students in the hybrid online course had significantly lower autonomy, competence, and relatedness perceptions, as well as lower autonomous motivation scores, compared to the traditional and large active learning courses. Next, students were purposefully selected based on the survey results to participate in semi-structured interviews with two members of the research team. The qualitative analysis of our interview data revealed specific aspects of each course type that were contributing to students’ perceptions of their competence, autonomy, and relatedness. Specifically, the large active learning course structure provided the most opportunities to support students’ motivation. Implications for mathematics faculty include incorporating active learning experiences in the classroom, since this study revealed that having opportunities to consistently interact with their peers and the instructor supported students’ basic psychological needs