전기 분무 방사법을 이용한 자가가습이 가능한 고분자 전해질 연료전지 막전극접합체 제조 및 성능 평가

Abstract

Proton exchange membrane fuel cells (PEMFCs) are some of the most efficient electrochemical energy sources for transportation applications because of their clean, green, and high efficiency characteristics. Various electrode deposition methods, such as air-brushing, decal transfer, screen printing and electrostatic spraying, have been explored to fabricate high-performance catalyst layer for proton exchange membrane fuel cells. Among them, the electrostatic spray deposition dragged a great attention due to the improved fuel cell performance at extremely low platinum mass loading. In this study, the effect of mass loading of platinum by using the electrostatic spray deposition was investigated systematically. The electrode morphology of the electrostatic sprayed catalyst layer is compared with that of the conventional decal-transferred catalyst layer to highlight its unique microstructure. As a result, the electro-sprayed catalyst layer showed 1.67 times higher current density at 0.5 V as compared to the decal-transferred catalyst layer. Thus, it can be suggested that a great deal of efforts must put onto the microstructure of the catalyst layer to overcome the severe performance decrease at low platinum loading. In the second research part, the effect of the solvent on the catalyst layer of PEMFC membrane electrode assembly (MEA) fabricated using the electrostatic spray deposition method was studied. The optimization of catalyst layer morphology is considered a feasible approach to achieve high performance of PEMFC MEA. The catalyst ink comprised of Pt/C, a Nafion ionomer, and a solvent. Two types of solvent were used: isopropyl alcohol (IPA) and dimethylformamide (DMF). Compared with the catalyst layer prepared using IPA-based ink, the catalyst layer prepared with DMF-based ink had a dense structure because the DMF dispersed the Pt/C-Nafion agglomerates smaller and more homogeneously. The size distribution of the agglomerates in catalyst ink was confirmed through Dynamic Light Scattering (DLS) and the microstructure of the catalyst layer was compared using field emission scanning electron microscopy (FE-SEM). In addition, the electrochemical investigation was performed to evaluate the solvent effect on the fuel cell performance. The catalyst layer prepared with DMF-based ink significantly enhanced the cell performance (0.45 A cm-2 at 0.68 V) compared with that fabricated using IPA-based ink (0.13 A cm-2 at 0.68 V) due to the better dispersion and uniform agglomeration on the catalyst layer. In the last part of the research, the nano-sized dense-structure (NSDS) layer, which is the role of the maintain the cell performance at zero relative humidity, was studied. An issue with PEMFC is to maintain the high proton conductivity at a low relative humidity. One way to address this issue, as our group has reported previously, is to introduce the NSDS layer, which is the role of the retain the humidification level by recirculating the generated water. In this study, a simple fabrication process of NSDS layer was developed using the electrostatic spray deposition. This method allows the creation of evenly distributed pores with diameters smaller than 80 nm, thus contributing to the enhanced water retention. As a result, the fuel cell performance of the MEA employing the NSDS layer showed 2 times elevated current density at 0.68 V compared to that of the conventional MEA under 0% RH condition, due to the promoted humidification level. Moreover, the water retention mechanism in the MEA employing NSDS layer was investigated by tracking the water pathway via 3D tomography-based direct numerical simulation.