Results 1 - 10 of 3133
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[en] We present two data-driven modeling methods, partial least square (PLS) and artificial neural network (ANN), to predict the major operating and performance variables of a polymer electrolyte membrane (PEM) fuel cell stack. PLS and ANN models were constructed using the experimental data obtained from the testing of a 30 kW-class PEM fuel cell stack, and then were compared with each other in terms of their prediction and computational performances. To reduce the complexity of the models, we combined a variables importance on PLS projection (VIP) as a variable selection method into the modeling procedure in which the predictor variables are selected from a set of input operation variables. The modeling results showed that the ANN models outperformed the PLS models in predicting the average cell voltage and cathode outlet temperature of the fuel cell stack. However, the PLS models also offered satisfactory prediction performances although they can only capture linear correlations between the predictor and output variables. Depending on the degree of modeling accuracy and speed, both ANN and PLS models can be employed for performance predictions, offline and online optimizations, controls, and fault diagnoses in the field of PEM fuel cell designs and operations
[en] A novel Pd-Pt catalyst formation process was proposed for reduction of Pt usage. In our miniature fuel cells, porous Pt was used as the catalyst, and the Pt usage was quite high. To reduce the Pt usage, we have attempted to deposit Pt on porous Pd by galvanic replacement, and relatively large output was demonstrated. In this study, in order to reduce more Pt usage and explore the alloy catalyst formation process, atomic layer deposition by UPD-SLRR (Under Potential Deposition – Surface Limited Redox Replacement) was applied to the Pd-Pt catalyst formation. The new process was verified at each process steps by EDS elemental analysis, and the expected spectra were obtained. Prototype cells were constructed by the new process, and cell output was raised to 420mW/cm2 by the Pd-Pt catalyst from 125mW/cm2 with Pd catalyst
[en] Core@shell nanocrystals (NCs) have been widely explored for oxygen reduction reaction (ORR). In this work, monodisperse PdCu@PtCu NCs with various shell thicknesses and compositions have been synthesized through a two-step protocol. As-synthesized PdCu@PtCu core@shell catalysts show enhanced specific activities (SAs) and mass activities (MAs) towards ORR. When PdCu/PtxCuy (core/shell) atomic ratio and Pt/Cu (x/y) ratio both reach 1/1, the core@shell catalyst exhibits the highest SA and MA (normalized with total mass of Pt and Pd). It is also found that the core@shell catalysts show drastically enhanced stability compared with pure PtCu alloy catalyst. It is proposed that both the activity and stability enhancements can be ascribed to the electronic interaction or charge transfer between Pd atoms (in core) and the shell elements. This work demonstrates a new family of core@shell catalysts that can be potentially used as cathode electro-catalysts in fuel cells.
[en] This book explains chemical equilibrium with nature and characteristic of chemical equilibrium, law of mass action and direction of chemical equilibrium, acid-base equilibrium with principle of acid and base and amino acid, solubility and precipitation equilibrium with equilibrium of solubility, complex ion and solubility, electrochemistry on oxidation-reduction reaction, battery and fuel cell, decay and electrolysis, chemical reaction speed and nuclear reaction with Michaelis-Menten mechanism safety of nuclear, transition elements and coordination compound with introduction, name, structure and ligand EDTA and solid structure with categorization of solid and unit cell.
[en] In this work, two approaches have been combined to elaborate bio-functionalized interfaces having an original structure and well defined at several characteristic scales. These two approaches are 1)the growth of conducting or non conducting materials through organized structures and 2)the chemistry of non-covalent intermolecular bonds leading to the assembling of molecules towards interfacial structures having greatest size. With a deep physico-chemical characterization, it has been possible to understand the properties of these multi-scale structures and to propose different applications fields as for instance bio-electro-catalysis or photovoltaic cells. (O.M.)
[en] The structural change of Nafion polymer electrolyte membrane (PEM) induced by hot-pressing, which is one of the representative procedures for preparing membrane-electrode-assembly for low temperature fuel cells, was investigated by 2H nuclear magnetic resonance (NMR) spectroscopy. The hydrophilic channels were asymmetrically flattened and more aligned in the membrane plane than along the hot-pressing direction. The average O-2H director of 2H2O in polymer electrolyte membrane was employed to extract the structural information from the 2H NMR peak splitting data. The dependence of 2H NMR data on water contents was systematically analyzed for the first time. The approach presented here can be used to understand the chemicals' behavior in nano-spaces, especially those reshaping and functioning interactively with the chemicals in the wet and/or mixed state
[en] Microbial electrode catalysis such as microbial fuel cells or electrosynthesis involves electron exchange with the electrodes located at the cell exterior; i.e., extracellular electron transport (EET). Despite the vast amount of research on the kinetics of EET to optimize the catalysis rate, the relevance of other factors, including upstream metabolic reactions, has scarcely been investigated. Herein, we report an in vivo electrochemical assay to confirm whether EET limits anodic current production (j) for the lactate oxidation of Shewanella oneidensis MR-1. Addition of riboflavin, which specifically enhances the EET rate, increased j only in the early phase before j saturation. In contrast, when we removed a trace metal ion necessary for upstream reactions from the electrolyte, a significant decrease in j and the lactate consumption rate was observed only after j saturation. These data suggest that the limiting factor for j shifted from EET to upstream reactions, highlighting the general importance of enhancing, for example, microbial metabolism, especially for long-standing practical applications. Our concept to specifically control the rate of EET could be applicable to other bioelectrode catalysis systems as a strategy to monitor their rate-limiting factors.
[en] Atomic-scale structures of oxygen reduction reaction (ORR) active sites in non-platinum group metal (non-PGM) catalysts, made from pyrolysis of carbon, nitrogen, and transition-metal (TM) precursors have been the subject of continuing discussion in the fuel cell electrocatalysis research community. Quantum chemical modeling is one path forward for understanding of these materials and how they catalyze the ORR. We here demonstrate through literature examples of how such modeling can be used to better understand non-PGM ORR active site relative stability and activity and how such efforts can also aid in the interpretation of experimental signatures produced by these materials.