The catalyst layer (CL) in proton exchange membrane fuel cells (PEMFC) is a composite material comprised of carbon-supported Pt bonded with proton-conductive ionomer. Resistances associated with processes in the CL, e.g. proton conduction through the ionomer percolation within CL, contribute to the voltage loss during the fuel cell operation. In this study, we attempt to characterize CLs from several aspects [1]. A DSC study was carried out to investigate the possible component interactions in the CL. As shown in Fig.1, in a nitrogen environment, an endothermic peak appeared around 100ºC for a dried Pt/Vulcan and Nafion mixed catalyst ink and at 135ºC for a Pt/Nafion mixture. However, this peak was not observed in a Carbon/Nafion mixture implying distinct interactions between each component. TEM was also adopted to further investigate the microstructure of CLs. Moreover, the proton conductivity of CL using Nafion and BPSH as ionomer were measured respectively via the method proposed by Liu et al[2]. The effects of ionomer/carbon ratio relative humidity and ionomer equivalent weight on CL proton conductivity, will be discussed. Reference: [1]H. Iden, A. Ohma, and K. Shinohara, “Analysis of Proton Transport in Pseudo Catalyst Layers,” Journal of The Electrochemical Society, vol. 156, no. 9, p. B1078, 2009. [2] Y. Liu et al., “Proton Conduction and Oxygen Reduction Kinetics in PEM Fuel Cell Cathodes: Effects of Ionomer-to-Carbon Ratio and Relative Humidity,” Journal of The Electrochemical Society, vol. 156, no. 8, p. B970, 2009.
Proton Exchange Membrane Fuel Cells (PEMFC) are considered one of the most promising alternative energy technologies due to the low operation temperature, compact structure and wide range of applications, among other advantages 1. The demand for low platinum loading in PEMFC electrodes has driven recent research on electrode structure-function correlations. The structure and morphology of the electrode layer play important roles in controlling many aspects of fuel cell performance. Within the catalyst layers (CLs), the hydrogen oxidation and the oxygen reduction reactions take place, involving complex mass and charge transport processes (diffusion of reactants and products, migration and diffusion of protons, migration of electrons, permeation, electroosmotic drag, as well as vaporization/condensation of water) 2. Previous studies performed on the influence of the ionomer loading on the catalyst layers has shown that this parameter has an effect on the dispersion of the carbon aggregates, the thickness of Nafion® films covering the catalyst/carbon surface and therefore the porosity of the CLs. Typical loadings for Nafion® ionomer have been reported to be within the range of 30-40% 3. In this study, the microstructure of PEMFC electrodes with different variations in terms of ionomer to carbon (IC) ratios, ionomer equivalent weights and electrode thickness (by means of variations in Pt loading) were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) nitrogen adsorption, including materials dispersion and porosity in CLs for freestanding electrodes (Figure 1). Some images of a typical catalyst layer are shown in Figure 1. Several typical features are shown here, providing indications of the large-scale porosity of the layer as well as images showing expanses of ionomer with and without embedded Pt particles. In previous studies4, measurements of water transport in similar CLs suggested that sub-saturated catalyst layers have a less connected ionomer network than that expected from uniform coverage of particles in the layer. Microscopy and other measurements noted above on a series of systematically modified catalyst layers will be summarized in an attempt to assess this finding. Single cell performance with these catalyst layers was evaluated in order to analyze the relationship with the structure properties. Acknowledgements NMC gratefully acknowledges the support from a Fulbright Fellowship. Additional support was provided by the NSF EPSCoR program. Research supported at ORNL by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. References 1. A. L. W. Vielstich, H. A. G., Handbook of fuel cells, fundamentals, technology and applications 2003. 2. Zhang, J., PEM Fuel Cell Electrocatalysts and Catalyst Layers. Fundamentals and Applications. Springer London: 2008. 3. (a) Antolini, E.; Giorgi, L.; Pozio, A.; Passalacqua, E., Influence of Nafion loading in the catalyst layer of gas-diffusion electrodes for PEFC. Journal of Power Sources 1999, 77 (2), 136-142; (b) Sasikumar, G.; Ihm, J. W.; Ryu, H., Optimum Nafion content in PEM fuel cell electrodes. Electrochimica Acta 2004, 50 (2–3), 601-605. 4. Sun, C.-N. and Zawodzinski, T. A. ECS Electrochem Lett., 2012, 1 (5) F36-39.
Learning analysis has gradually become the focus of attention of the majority of educators, and data mining has brought more possibilities for learning analysis. This study takes CNKI literature as the research object, searches "data mining" and "learning analysis" as keywords, and the content analysis method is used to explore the application status of data mining technology in learning analysis researches. This study found that relevant research scenarios focus on online platforms and higher education. The research topics are mainly theoretical exploration and model construction to explore the rules of teaching and learning and analyze learners. Data collection gradually diversified, focusing on process data collection. Analysis method tends to be the comprehensive application of professional data mining method. In the future, the scope of research objects can be further expanded, classroom performance data, unstructured data and physiological data can be collected for analysis, and consider data privacy to guarantee the legal rights and interests of the participants.
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