Chowdhury Anamika, Bird Ashley, Liu Jiangjin, Zenyuk Iryna V, Kusoglu Ahmet, Radke Clayton J, Weber Adam Z
Energy Conversion Group, Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94720, United States.
ACS Appl Mater Interfaces. 2021 Sep 15;13(36):42579-42589. doi: 10.1021/acsami.1c07611. Epub 2021 Sep 7.
Transport phenomena are key in controlling the performance of electrochemical energy-conversion technologies and can be highly complex, involving multiple length scales and materials/phases. Material designs optimized for one reactant species transport however may inhibit other transport processes. We explore such trade-offs in the context of polymer-electrolyte fuel-cell electrodes, where ionomer thin films provide the necessary proton conductivity but retard oxygen transport to the Pt reaction site and cause interfacial resistance due to sulfonate/Pt interactions. We examine the electrode overall gas-transport resistance and its components as a function of ionomer content and chemistry. Low-equivalent-weight ionomers allow better dissolved-gas and proton transport due to greater water uptake and low crystallinity but also cause significant interfacial resistance due to the high density of sulfonic acid groups. These effects of equivalent weight are also observed ionic conductivity and CO displacement measurements. Of critical importance, the results are supported by ellipsometry and X-ray scattering of model thin-film systems, thereby providing direct linkages and applicability of model studies to probe complex heterogeneous structures. Structural and resultant performance changes in the electrode are shown to occur above a threshold sulfonic-group loading, highlighting the significance of ink-based interactions. Our findings and methodologies are applicable to a variety of solid-state energy-conversion devices and material designs.
传输现象是控制电化学能量转换技术性能的关键，且可能高度复杂，涉及多个长度尺度以及材料/相。然而，针对一种反应物物种传输进行优化的材料设计可能会抑制其他传输过程。我们在聚合物电解质燃料电池电极的背景下探讨此类权衡，其中离聚物薄膜提供了必要的质子传导性，但会阻碍氧气传输至铂反应位点，并由于磺酸根/铂相互作用而导致界面电阻。我们研究了电极的整体气体传输电阻及其各组分随离聚物含量和化学性质的变化。低当量重量的离聚物由于吸水性更强和结晶度低，使得溶解气体和质子传输更好，但由于磺酸基团密度高，也会导致显著的界面电阻。在离子电导率和一氧化碳置换测量中也观察到了当量重量的这些影响。至关重要的是，这些结果得到了模型薄膜系统的椭偏测量和X射线散射的支持，从而为模型研究探测复杂的异质结构提供了直接联系和适用性。结果表明，电极中的结构和由此产生的性能变化发生在磺酸基团负载阈值之上，突出了基于油墨的相互作用的重要性。我们的研究结果和方法适用于各种固态能量转换装置和材料设计。
