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: 2042758
• 负责人: Iryna Zenyuk
• 金额: $ 5.49万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2021-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2042758&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.

该项目的目标是了解多孔碳电极中的耦合传热和传质过程，以用于能量转换和存储。聚合物电解质燃料电池 (PEFC) 等能量转换设备有望最大限度地减少运输行业对环境的影响。然而，在低工作温度下，水管理仍然是一个大问题。当液态水积聚在薄薄的多孔碳层中时，由于反应物输送不足，电流密度会降低。成功的 PEFC 设计面临的挑战之一是了解多孔碳层中的耦合质量和热传输现象，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、混合润湿性碳材料中水传输的基本机制。将在纳米和微米尺度上通过温度梯度更好地理解蒸发机制。该项目的结果将增进对热梯度下水传输机制的理解，并为燃料电池、氧化还原液流电池和太阳能燃料等一大类能量转换和存储技术提供最佳电极设计路线图发电机。可再生能源主题将通过与 PI 能源软件平台集成的可用能源套件引入 K-12 课堂。将通过实践设计活动教授废热、效率、成本/效益分析和可再生能源的概念。此外，研究成果将由 PI 的本科生指导进行传播，并将其纳入电化学能量转换和存储课程中。混合润湿性、多孔碳层中的水管理对于开发和制造具有成本效益的 PEFC 至关重要。为了实现最大的水渗透，从而获得更高的燃料电池电流密度，有必要了解压力和毛细管驱动的液态水传输与多孔电极中蒸发/冷凝引起的相变诱导（PCI）流动之间的相互作用和气体扩散层（GDL）。 GDL 具有多功能作用，GDL 中的热和质量传输取决于材料形态和传输特性，例如导电性和导热性、气体扩散性和流体渗透性。尽管已经通过建模和实验探索了 GDL 中水传输的某些方面，但对这些材料内的蒸发和 PCI 流动仍然知之甚少。缺乏这种基础知识主要是由于进行实验测量和可视化这些多孔材料内蒸发水锋的挑战。最近的报告表明，在 GDL 中水位较低时，PCI 流量甚至更为显着，但其物理原因尚未完全理解。必须量化诱导热梯度下的水传输，以找到这些多孔层内精确的液体前沿分布。在该项目中，蒸发速率限制步骤将通过现场实验仪器进行确定，并使用 X 射线计算机断层扫描（X 射线 CT）对蒸发的滨水区进行可视化。通过在多孔电极的厚度上施加热梯度，可以探索分层电极中 PCI 流动的机制。预计会出现水再循环，并将利用纳米和微米 X 射线 CT 在厚度方向上进行可视化和量化。 X 射线 CT 的精确技术可以收集前所未有的详细信息，了解不同热梯度下水团簇的确切位置。同时，将测量通过这些电极的热量和质量传输。孔隙网络和连续体模型将用于帮助解释收集到的数据并预测新型材料结构。这一新的认识将被用来确定热和质量传输的最佳 GDL 形态的纳米和微米尺度特征。通过结合新颖的实验和建模功能，PI 将设计 GDL 设计来调节相变诱导流并有效管理 PEFC 中的水传输，从而提高可达到的功率密度。