摘要/Abstract
以碳纳米管（CNT）作为低铂载量膜电极（CCM）催化层（0.1 mgPt·cm-2）添加剂，研究了CNT的添加方式对催化层微观结构以及膜电极性能的影响.结果表明，与常规低铂载量催化层相比，在其表面喷涂一层CNT或将CNT均匀分散到Pt/C催化层中均有利于提升低铂载量膜电极的输出性能，在70℃和100%相对湿度条件下最高输出功率比常规低铂载量膜电极的0.522 W·cm-2分别提升了22.4%和60.0%，并且均匀分散添加方式优于分层添加方式.其原因在于分层添加CNT后改善了低铂催化层和气体扩散层之间的接触界面，降低了催化层与扩散层间的接触电阻，而均匀分散添加方式除了可降低界面接触电阻外，还显著改善了低铂催化层中的气体传输，大幅提升了Pt催化剂的利用效率，使得膜电极电化学反应电阻明显降低.进一步对均匀分散添加方式中CNT的载量进行优化，表明CNT添加量为37.5 μg·cm-2时电池输出性能最佳，70℃和100%相对湿度条件下的最大输出功率达到0.91 W·cm-2.本研究工作表明，将CNT均匀分散添加到催化层中是一种有效提升低铂载量膜电极性能的方法.
关键词: 质子交换膜燃料电池, 催化层, 碳纳米管, 低铂, 膜电极
The cell performance and Pt utilization of low-Pt proton exchange membrane fuel cells (PEMFCs) have been significantly improved through incorporating carbon materials into the conventional Pt/C catalytic layer of the membrane electrode assembly (MEA). However, the introduction methods for the carbon materials have not been investigated. In this work, carbon nanotube (CNT) as an additive was added to the low-Pt loading catalytic layer (0.1 mgPt·cm-2) by two methods:a separated CNT layer deposited on the top of the conventional Pt/C layer (CCM-1) and a mixture layer by blending CNT and Pt/C catalyst (CCM-2). The conventional low-Pt loading catalytic layer was employed as control group (CCM-0). The microstructure of the catalytic layers was characterized by scanning electron microscopy, transmission electron microscopy and nitrogen sorption isotherms method. The electrochemical properties of the catalytic layer and membrane electrode were evaluated by cyclic voltammetry (CV), electrochemical impedance (EIS) and linear scanning voltammetry. The results indicated that the cell performance of the conventional low-Pt loading catalyst coated membrane was improved by the introduction of CNTs in both CCM-1 and CCM-2. Compared to the conventional CCM (CCM-0) with a peak power density of 0.522 W·cm-2 at 70℃ and 100% relative humidity (RH) without backpressure, the maximum power densities of CCM-1 and CCM-2 have been improved by 22.4% and 60.0% under the same test conditions, respectively. The increased performance of CCM-1 is believed to result from the enhancement of contact interface between the catalytic layer and the gas diffusion layer in CCM-1 and consequent decrease of the contact resistance. Furthermore, the outstanding power density of CCM-2 is not only owing to the decreased interface contact resistance between the CCM and the gas diffusion layer, but also due to the significant improvement of gas transmission in the catalytic layer, which leads to the decrease of electrochemical reactant resistance and then improvement of the Pt utilization. That has been confirmed by the Pt utilization of 34.4%, 35.6% and 44.7% for CCM-0, CCM-1 and CCM-2. In addition, it also was confirmed by the extremely low power output (2.9 mW·cm-2) of a CCM with only CNT in the catalytic layer when the fuel cell was tested at 70℃ and 100% RH without back pressure. In addition, the optimum loading of CNT in the mixed catalytic layer is 37.5 μg·cm-2 with the peak power density of 0.91 W·cm-2. This work shows that mixing of CNT and Pt/C catalyst into a catalytic layer is an effective method for improving the Pt utilization and reducing the loading of Pt catalyst.
Key words: proton exchange membrane fuel cells (PEMFCs), catalytic layer, carbon nanotube, low-Pt loading, membrane electrode assembly
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