An experimental study of polymer electrolyte fuel cell operation at sub-freezing temperatures

The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society

Subfreezing operation of polymer electrolyte fuel cells: Ice formation and cell performance loss

In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid. © 2012 Elsevier Ltd. All rights reserved

Along-the-channel modeling and analysis of PEFCs at low stoichiometry: Development of a 1+2D model

Water management remains a key challenge in polymer-electrolyte fuel cells. In this work, a pseudo 3-D (1+2D) model is developed to account better for changes of water management along the channel, as well as verify the possibilities of using differential cells for data capture and translation to integral cell performance. An accurate 2-D membrane-electrode-assembly model is developed for differential cell modeling, which is combined with an along-the-channel stepping algorithm to account for down the channel changes in pressure, temperature, reactant concentration, and relative humidity. Variations in cell performance along the channel due to changes in operating conditions are characterized quantitatively and optimized, where drier feed conditions demonstratively require such an approach. Overall, the study identifies gaps between differential and integral cells including those related to flow velocity and highlights the need for better models to understand and link integral cell performance and water management

Faculty Perceptions of Using Synchronous Video-Based Communication Technology

Online learning has traditionally relied on asynchronous text-based communication. The COVID-19 pandemic, though, has provided many faculty members with new and/or additional experience using synchronous video-based communication. Questions remain, though, about how this experience will shape online teaching and learning in the future. We conducted a mixed method study to investigate faculty perceptions of using synchronous video-based communication technology. In this paper, we present the results of our inquiry and implications for future research and practice

Enhancing Stability and Efficacy of Trichoderma Bio-Control Agents through Layer-by-Layer Encapsulation for Sustainable Plant Protection

Agricultural fungicide pollution poses a significant environmental challenge and carries adverse consequences for human health. Therefore, strategies to limit fungicide usage have gained paramount importance. Trichoderma fungi, owing to their antagonistic activity against various pathogenic fungi, have emerged as prospective candidates for enhancing both the effectiveness and sustainability of plant protection. Nevertheless, the utilization of bio-control agents like Trichoderma has unveiled new challenges, notably their vulnerability to physical stimuli and diminished efficacy during prolonged storage. To overcome these drawbacks, we present a mild and scalable encapsulation method for Trichoderma spores, employing a layer-by-layer (LbL) encapsulation approach using biobased lignin derivates. Our investigations demonstrate that the LbL-encapsulation technique imparts remarkable improvements in spore stability, even under adverse conditions such as variable temperature and prolonged exposure to UV irradiation compared to unencapsulated spores. Notably, encapsulated Trichoderma spores exhibit increased efficiency in the cultivation of tomato plants when compared to their unencapsulated counterparts. Additionally, our findings reveal that the in planta efficacy of encapsulated spores is contingent upon the specific Trichoderma strain employed. The results outlined herein suggest that Trichoderma spores, encapsulated within lignin through the LbL approach, exhibit potential as promising and sustainable alternative to chemical fungicides and potential commercialization