质子交换膜燃料电池催化层中水传输机理与电池性能耦合规律的研究

The presence of water in the catalyst layer and membrane is considered essential for proton transport, cell performance and durability. There are several processes, such as water sorption, desorption and diffusion involved in the water transfer in the catalyst layer and at interface in an operating PEMFC. Because of the coupling with electrochemical performance, understanding the water transfer and water balance is critical to the advancements of PEMFC technology. Although many studies on water transfer through the membrane and overall water balance in an operating PEMFC have been concluded, a comprehensive study that correlates and validates ex-situ and in-situ water transfer in the catalyst layer has not been reported yet. This study is driven by a motivation of obtaining a better fundamental understanding of water transport in the catalyst layer and interface between the catalyst layer and membrane under operating PEMFC. In order to approach the objective, several experimental setups and schemes were designed and implemented, including ex-situ water transfer measurement setups, and experimental setups for in-situ fuel cell testing and water balance studies. Insights would be useful for selecting operating conditions for improved fuel cell operation and designing novels membrane. Moreover, parameters found could be employed in systematic modeling studies to simulate PEM with varying transport properties.

质子交换膜燃料电池(PEMFC)中水在催化层和界面间传递形态与传递方式对电池放电性能和使用寿命至关重要。本项目拟通过构建先进、实效的测定水在催化层和界面间传递的现场与非现场的检测系统，实验测定同理论数学模型结合，深入研究水在催化层的多尺度微流道内传递形态、传递方式与电化学反应、多尺度结构及传质过程的耦合规律，揭示水在催化层中和界面间传递机理及调控机制，对提高电池性能、稳定性、可靠性以及寿命，具有重要的理论与实际意义。

项目围绕水在催化层与电解质膜及其界面的传输，较为系统地研究了水吸附、脱附特性、存在形态、传递方式与催化层与电解质膜微观结构的关系，并建立了多组分、多尺度的数学模型从微观上描述水在多尺度微孔道内和界面间的传递特性。 首先，针对催化层多孔、脆弱，自身缺乏自支撑，催化层与基底的孔隙难以分离，致使误差偏大，无法准确获取催化层孔径结构信息的技术难题，创新性地发展了测量催化层孔径结构和孔隙率的新方法，提高了测量精确度。然后，采用自搭的非现场实验装置、动态水蒸气吸附仪及在线水收集系统，研究了不同温度和不同增湿度下催化层和电解质膜中水的存在形态和传递方式、吸脱附动力学特征。研究发现，水可以液-液、液-气、气-气等三种形态在电解质膜中传递，具体形态同工作温度、湿度相关。随着电解质膜厚度减小、温度升高及水活度提高，水的渗透阻力会降低。催化层中水的传递方式与传递形态同电解质膜的相似，由于催化层的多孔结构，主要以液-液传递形式为主，渗透阻力同催化层中碳载体、Nafion 含量、孔隙率、温度及气体压力相关。传输阻力随Nafion 含量增加和孔隙率的减小而增加，随温度升高和水活度增加而降低。水在界面间的传输阻力主要源于催化层，可以液-液、液-气、气-气等三种形态由电解质膜向催化层传递，而由催化层向电解质膜的传递形态难以确定。项目的研究成果为阐明水在催化层与界面间传递规律、转化机制，电极结构优化提供一定实验依据和理论指导。