The research on separation of resistances in electrode of polymer electrolyte membrane fuel cell

Abstract

Environmental problems are getting worse because of the greenhouse effect from overuse of fossil fuels. The carbon dioxide from fossil fuels spreads into the atmosphere and acts as a greenhouse that covers the earth, raising the earth's temperature. Therefore, renewable energy has become essential to reduce the use of fossil fuels and carbon dioxide emissions. Hydrogen energy is also becoming very important because it has high chemical energy per mass, and only water comes out as a by-product when it is converted into electrical energy. The fuel cell is a device that converts the chemical energy of a reaction in which oxygen and hydrogen react to form water into electrical energy. When hydrogen is supplied from the fuel cell anode, it is spontaneously decomposed into hydrogen ions. Hydrogen ions move to the cathode through the electrolyte and react with supplied oxygen to produce water. However, in this process, there is resistance to the activation energy of the reaction and the movement of ions and gases, which leads to energy loss. Therefore, reducing this energy loss plays an important role in increasing fuel cell performance. In this study, resistance analysis was conducted on changes in electrode properties and performance of high- and low-temperature fuel cells due to changes in materials. In the first chapter, the basic reaction mechanisms and materials of high- and low-temperature polymer membrane electrolyte fuel cells are introduced, and the basic concepts of electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) resistance analysis are explained. In the second chapter, the physical properties were analyzed for four gas diffusion layers, and gas diffusion electrodes (GDEs) for the cathode of HT-PEMFC were fabricated through bar coating with three B/C (binder to carbon) ratios. Among them, The GDE from JNT30-A6P showed a significant change in secondary pore volume at a B/C ratio of 0.31, which had the largest pore volume among all GDEs. In the polarization curve, JNT30-A6P GDE showed the best membrane electrode assembly (MEA) performance with a peak power density of 384 mW cm-2 at a B/C ratio of 0.31. From the DRT, the peak 1 corresponding to the mass transfer resistance of oxygen reduction reaction (ORR) was significantly reduced in the JNT30-A6P GDE. In the third chapter, resistance analyses are conducted to elaborate on the performance and durability improvements induced by the adsorption of [MTBD][beti] ionic liquid (IL) on PtCo/C catalyst. The morphological changes caused by IL adsorption are observed on micro and macro scales via physicochemical methods. From the half-cell measurement, when the 4 wt.% IL was adsorbed, a 15 mVRHE improvement in ORR activity occurs; as the adsorption amount increases, the activity decreases, but the anion poisoning resistance increases. The single cell outperforms 1.3 times higher current density at 0.8 V and 40% decreased charge transfer resistance by 8 wt.% IL adsorption. DRT resistance analysis reveals that ORR charge transfer resistance (RORR) and proton charge transfer resistance (Rproton) decrease due to IL adsorption. During accelerated durability tests, 8 wt.% IL-loaded MEA showed a 20% increase in durability, and a lower degradation of RORR and Rproton encouraged improved durability.