The Nature of Coupled Heat and Mass Transport in Porous Carbon Electrodes

多孔碳电极中热质耦合传递的本质

• 批准号: 1605159
• 负责人: Iryna Zenyuk
• 金额: $ 29.35万
• 依托单位: Tufts University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2020-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1605159&HistoricalAwards=false
• 关键词: Nature; Coupled; Heat; Mass; Transport

The goal of this project is to understand coupled heat- and mass-transport processes in porous carbon electrodes for applications in energy-conversion and storage. Energy-conversion devices, such as polymer electrolyte fuel cells (PEFCs), hold great promise for minimizing the environmental impact of the transportation sector. However, water management is still a large problem at low operating temperatures. As liquid water accumulates in the thin, porous carbon layers, current density decreases due to inadequate reactant delivery. One of the challenges in successful PEFC design is understanding the coupled mass and thermal transport phenomena in porous carbon layers to optimize water management and increase power output, improving PEFC performance. The proposed project will determine the fundamental mechanisms of water transport in porous, mix-wettability carbon materials. Greater understanding of evaporative mechanisms via temperature gradients will be achieved on the nano- and micro-scales. The results of the project will advance the understanding of water transport mechanisms under thermal gradients and provide a roadmap of optimal electrode design for a large class of energy-conversion and ?storage technologies, such as fuel cells, redox-flow batteries and solar-fuel generators. The topic of renewable energy will be brought into K-12 classrooms through available energy kits integrated with the PI's energy software platform. The concepts of waste heat, efficiency, cost/benefit analysis, and renewable energy will be taught with hands-on design activities. Additionally, research findings will be disseminated by PI's undergraduate mentoring and incorporation in an electrochemical energy-conversion and -storage course.Water management in mix wettability, porous carbon layers is critical to developing and manufacturing cost-effective PEFCs. To achieve maximum water permeation, and consequently higher fuel cell current densities, it is necessary to understand the interplay between pressure- and capillary-driven liquid-water transport and phase-change induced (PCI) flow due to evaporation/condensation in the porous electrodes and gas-diffusion layers (GDLs). GDLs serve multifunctional roles, and heat and mass transport in GDLs depends on both material morphology and transport properties, such as electrical and thermal conductivity, gas diffusivity, and fluid permeability. Although some aspects of water transport in GDLs have been explored with modeling and experiments, evaporation and PCI flow within these materials are still poorly understood. This fundamental knowledge is lacking primarily due to the challenge of taking experimental measurements and visualizing evaporating water front within these porous materials. Recent reports suggest that PCI flow is even more significant at lower water levels in GDLs, however the physical reasons for this are not fully comprehended. It is imperative to quantify water transport under induced thermal gradients to find exact liquid front distribution within these porous layers. In this project, the evaporation rate-limiting step will be identified with in-situ experimental instrumentation and evaporating water-fronts will be visualized using X-ray computed tomography (X-ray CT). The mechanisms of PCI flow in hierarchical electrodes will be explored by imposing thermal-gradients across the thickness of the porous electrode. Water recirculation is expected and will be visualized and quantified in the through-thickness direction utilizing nano- and micro- X-ray CT. The precise techniques of X-ray CT allow the gathering of an unprecedented level of detailed information on the exact location of water clusters under varied thermal gradients. Simultaneously, heat and mass-transport through these electrodes will measured. Pore-network and continuum models will be used to help interpret the gathered data and predict novel material architectures. This new understanding will be leveraged to identify nano- and micro-scale characteristics of optimal GDL morphologies for heat and mass-transport. Through combined novel experimental and modeling capabilities the PIs will engineer GDL designs to modulate phase-change induced flow and effectively manage water transport in PEFCs, thereby increasing the attainable power density.

该项目的目的是了解多孔碳电极中的热和质量传输过程，以应用于能量转换和存储中。能量转换设备，例如聚合物电解质燃料电池（PEFC），具有最小化运输部门的环境影响的巨大希望。但是，在低工作温度下，水管理仍然是一个大问题。随着液态水在薄的多孔碳层中积聚，由于反应物递送不足，电流密度降低。成功PEFC设计的挑战之一是了解多孔碳层中的量质量和热传输现象，以优化水管理并增加功率输出，从而提高PEFC性能。拟议的项目将确定多孔混合性碳化性碳材料中水运输的基本机制。通过温度梯度将对纳米尺度和微尺度上的温度梯度进行更深入的了解。该项目的结果将提高对热梯度下的水传输机制的了解，并为大型的能量转换和“储存技术，例如燃料电池，氧化还原电池和太阳能发电机”提供最佳电极设计路线图。可再生能源的主题将通过与Pi的Energy Software平台集成的可用能源套件一起进入K-12教室。动手设计活动将教授废热，效率，成本/收益分析和可再生能源的概念。此外，研究结果将由PI的本科指导和融合在电化学能源转换和 - 储存课程中。多孔碳层对于开发和制造成本效益的PEFC至关重要。为了达到最大的水渗透，因此燃料电池电池的密度更高，有必要了解由于多孔电极和气体 - 膨胀层（GDLS）中蒸发/凝结而导致压力和毛细管驱动的液体水运输和相变诱导的（PCI）流量之间的相互作用。 GDL扮演多功能角色，GDL中的热量和质量转运取决于材料形态和转运性能，例如电导率和热导率，气体扩散率以及流体渗透性。尽管已经通过建模和实验探索了GDL中的水运输的某些方面，但这些材料中的蒸发和PCI流仍然知之甚少。这种基本知识主要是由于进行实验测量和可视化这些多孔材料中蒸发的水面的挑战。最近的报道表明，在GDL中，PCI流量在较低的水位上更加重要，但是尚未完全理解其物理原因。必须在诱导的热梯度下量化水传输，以在这些多孔层中找到精确的液体前部分布。在这个项目中，将使用原位实验仪器来识别蒸发速率限制步骤，并使用X射线计算机断层扫描（X射线CT）可视化蒸发水面。通过在多孔电极厚度上施加热梯度，将探索层次电极中PCI流动的机理。预期水的再循环，并将使用纳米和微X射线CT在整个厚度方向上进行可视化和量化。 X射线CT的精确技术允许收集有关各种热梯度下水簇的确切位置的前所未有的详细信息。同时，将测量通过这些电极的热量和质量传输。孔网和连续模型将用于帮助解释收集的数据并预测新颖的材料体系结构。将利用这种新的理解来确定热和大众传播的最佳GDL形态的纳米和微尺度特征。通过新型实验和建模功能，PI将设计GDL设计以调节相变诱导的流量并有效地管理PEFC中的水运输，从而增加可实现的功率密度。