ECS Meeting Abstracts EIS and CV Characteristics of Pt Cathode Catalyst in PEMFC To cite this article: Shingo Kanazawa et al 2012 Meet. Abstr. MA2012-02 149 View the article online for updates and enhancements. This content was downloaded from IP address 5.171.36.103 on 31/07/2022 at 10:45 Abstract #149, Honolulu PRiME 2012, © 2012 The Electrochemical Society Department of Metallurgy and Ceramics Science Graduate School of Science and Engineering Tokyo Institute of Technology 2-12-1 O-okayama, Meguro-ku, Tokyo, Japan Introduction Proton exchange membrane fuel cell (PEMFC) is expected to be commercialized as automotive and stationary power supply. However, performance of PEMFC is limited by the slow kinetics of oxygen reduction reaction (ORR) [1]. Therefore, a quantitative evaluation of the ORR at the cathode catalyst is necessary. Cyclic Voltammetry (CV) has been used to evaluate electrochemical active surface area (ECA) from hydrogen adsorption/desorption, but is difficult to characterize the ORR of Pt cathode. In this study, electrochemical impedance spectroscopy (EIS) has been applied to evaluate the cathode catalyst of PEMFC. The relationship is clarified between the ECA obtained from CV and EIS parameters such as solution resistance (Rsol), charge transfer resistance (Rct) and double layer capacitance (Cdl). Reference [1] M.Lee, M.Uchida, D.A.Tryk, H.Uchida, M.Watanabe, Electrochimica Acta, 56, 4783-4790 (2011). 4 (4)0.22mg/cm2 Experimental All the measurements were made on an assembled PEMFC under four different conditions by changing the composition of MEA. The four types of MEAs were made by changing the amount of Pt loading, the thickness of cathode catalyst layer and by changing the ratio of Pt/C as shown in Table 1. In all the cases, the anode catalyst was the same. Before the start of CV, the cell was left at OCV for 15 min so that a stable OCV is obtained. Thereafter, 30 cycles of CV were performed in between 0.6-1.0 V at 100 mV/s. The electrochemical impedance measurements were done at 0.7 V with the amplitude of ac signal as 10 mV and frequency range was from 20 kHz to 1 mHz. Results and Discussion Figure 1 shows CVs of PEMFC with four different MEAs with different amount of Pt loadings. The ECA of Pt cathode under four different conditions was estimated from the Hupd in the CV. The obtained values are shown in Table 2. Nyquist plots of four different MEAs measured at 0.7 V are shown in Fig. 2. There appears only one semicircle, although the impedance was scatted in the low frequency region.From this plot, the double layer capacitance Cdl value was estimated from the frequency of a top of the semicircle. The Rsol value was estimated from high frequency and Rct value was estimated from low frequency. If compared the results of MEAs (1) and (3) in Table 2, it is found that the ECA and Cdl increase with increasing Pt (3)1.03mg/cm2 (2)0.52mg/cm2 0 -2 (1)0.25mg/cm2 -4 -6 0 0.2 0.4 0.6 0.8 1 Voltage, E / V Fig.1 CVs of PEMFC with four different 100mV/s. 35 MEAs at 12 30 10 25 ImZ / mΩ Table 1 Summary of compositions of MEAs Thickness ratio of Pt/C Pt loadings 2 MEA No. cathode catalyst Wt% mg/cm layer to MEA(1) (1) 50 0.28 1 (2) 50 0.52 2 (3) 50 1.03 4 (4) 30 0.22 2 2 ImZ / mΩ Shingo KANAZAWA, Eiji TADA, Atsushi NISHIKATA, Tooru TSURU loadings. The Cdl for MEA (4) is higher than that for MEA (1), although they have the same Pt loading and different amounts of carbon. It indicates that the obtained Cdl will be sum of capacitance for Pt/Nafion and carbon/Nafion interfaces. The obtained Rsol values of MEA (1)-(4) are independent of the thickness of the cathode catalyst layer. Thus, it corresponds to the ionic resistance of Polymer electrolyte. If the Rch of MEAs (2)-(4) which are the same MEA thickness and different Pt loading, it is found that the Rch decreases with increasing Pt loading. This indicates the Rch corresponds to a charge transfer resistance of the ORR. On the other hand, MEAs (1)-(3) indicates almost same Rct, although they have different Pt loading. It means that for the MEAs (2) and (3) with the thicker cathode catalyst layers, much larger amounts of Pt catalyst does not work as active cathode sites. Current density, i / Acm-2 EIS and CV Characteristics of Pt Cathode Catalyst in PEMFC 20 8 6 (1) 0.28mg/cm2 (3) 1.03mg/cm2 (2) 0.52mg/cm2 4 2 15 0 (4) 0.22mg/cm2 10 0 2 4 6 8 ReZ / mΩ 10 12 5 0 0 5 10 15 20 ReZ / mΩ 25 30 35 Fig.2 Nyquist plot measured at 0.7 V for PEMFC with various MEAs as listed in Table 1. Table 2 Summary of ECA, Cdl, Rsol and Rct of four MEAs estimated from CV and Nyquist plots MEA ECA Cdl Rsol Rct No. cm2 F Ω Ω (1) 4320 0.57 2.4 8.6 (2) 7050 1.03 2.3 6.7 (3) 14300 1.97 2.3 8.4 (4) 5020 0.97 3.0 26.0
