Supporting Information

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1 Supporting Information Effect of water electrolysis catalysts on carbon corrosion in polymer electrolyte membrane fuel cells Sang-Eun Jang, Hansung Kim* Department of Chemical and Biomolecular Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul , Republic of Korea 1. Experiment 1.1 Synthesis of iridium oxide (IrO 2 ). IrO 2 was made by proprietary modification of the Adams-type fusion of the iridium salt in nitrate flux. 350mg of H 2 IrCl 6 xh 2 O (Johnson Matthey Co.) was dissolved in 10ml of ethanol/isopropanol (volume ratio 1:1) and vigorous stirred for 1 hour. Afterward, 10g of finely ground NaNO 3 (Duksan pure chemical Co.) was added into solution. This mixture was heated at 60 o C until dry and further dried in a convection oven at 80 o C for 30min. The dry salt mixture was finely ground and heat-treated at 500 o C for 30min in a continuous flow of air. Finally, the mixture was washed with deionized water until no Cl - was detected to obtain the oxide product. Crystalline structure of synthesized IrO 2 was characterized by X-ray diffraction (XRD) using a Cu Kα source operated at 40keV. Diffraction patterns were collected from 20 to 70 o at a scanning rate of 2 o per minute. 1.2 Preparation of membrane electrode assembly (MEA). A commercial Pt/C catalyst from Johnson Matthey Co. (40wt% Pt) was used for the anode. The anode catalyst loading was 0.4mg cm -2. Physical mixture of commercial Pt/C catalyst from Tanaka Kikinzoku Kogyo Co. (50wt% Pt, corrosion resistance) and synthesized Iridium oxide (IrO 2 ) were used for the cathode. The amount of IrO 2 added is 2 wt% of Pt/C catalyst. The catalyst S1

2 was ultrasonically mixed with 5wt% Nafion ionomer in isopropanol. Next, the mixed slurry was spray-deposited onto a Nafion 212 membrane of 5cm 2 cell geometric area using a hand sprayer with a high pressure N 2 carrier gas. The Pt loading is fixed at 0.4 mg cm Corrosion test and electrochemical analyses. Electrochemical analysis was performed to examine the physical and electrochemical changes before and after corrosion tests. Polarization curves of MEA were obtained using a commercial test system (Fuel Cell Technologies Inc.) at a cell and humidification temperature of 75 o C under ambient pressure with O 2 at the cathode (150 ccm) and H 2 at the anode (150 ccm) at STP (standard temperature and pressure). Cyclic voltammetry (CV) was performed in the range V NHE at a sweep rate of 50mV s -1 to measure the active Pt surface area using a mutipotentiaostat (VSP from Bio Logic Science Instruments). Prior to CV, the cathode was purged with nitrogen gas for 40 min to remove oxygen in the cell. After completion of CV, carbon corrosion tests were followed. The corrosion test was conducted with application of 1.6 V constant potential against hydrogen anode electrode of fuel cell at a cell and humidifier temperature of 70 for 30min. During the corrosion test, the cathode was exposed to a humidified N 2 at a flow rate of 30ccm, whereas humidified H 2 at a flow rate of 20 ccm was supplied to the anode. The gas provider is Daesung Industrial Gases and the purity of each gas is H 2 (99.999%), O 2 (99.995%) and N 2 ( ). CO 2 emission during the corrosion test was quantified as a function of time using on-line mass spectrometry (Hiden Analytical DSMS). After the corrosion test, MEAs were reactivated for the performance to be allowed to reach a steady state. Polarization curves and CV were then measured for comparison before the corrosion test. S2

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4 Figure S2. Nyquist plots of MEAs before and after corrosion test. (a) MEA without IrO 2, (b) MEA with IrO 2. The experiments were performed at 0.8V in the frequency range between 0.1 and 1 khz. The ohmic resistances were and Ω for the MEAs with and without IrO 2, respectively. The addition of IrO 2 does not influence on the change in the resistance. The charge transfer resistance of MEA without IrO 2 increased by 92.5% (from Ω to Ω) while that of MEA with IrO 2 showed a little difference after the corrosion test. S4

5 (b) 2wt% IrO2 O 2 (ppm) O 2 (ppm) Time (min) (a) 0wt% IrO Time (min) Figure S3. Comparison of O 2 mass spectra for the MEAs (a) without IrO 2 and (b) with IrO 2 in the cathode catalyst layer of the PEMFC. Corrosion tests were performed at 1.6V for 30 min. The cell and humidification temperature were 70 o C. The flow rate of H 2 (anode side) was 20 ccm and N 2 (cathode side) was 30ccm. The total amounts of O 2 generation of without IrO 2 and with IrO 2 were 1446 µl and µl, respectively. S5

6 25 20 IrO 2 Pt Current (ma) Potential (V NHE ) Figure S4. The polarization curves of synthesized iridium oxide and commercial platinum black catalysts in oxygen evolution reaction. Measurements were performed from 1.24 V NHE to 1.84 V NHE using a rotating disk electrode in a nitrogen-saturated 0.5M H 2 SO 4 solution at a sweep rate of 5 mv s -1 and a rotating rate of 1200 rpm in order to remove oxygen bubbles generated on the surface of electrode. The total amount of catalyst was fixed at 50.5 µg cm -2. S6

7 rpm 900 rpm 1200 rpm 1800 rpm Current (ma) Potential (V NHE ) Figure S5. The polarization curves of synthesized Iridium oxide in oxygen evolution reaction. Measurements were performed from 1.24 V NHE to 1.84 V NHE using a rotating disk electrode in nitrogen-saturated 0.5M H 2 SO 4 solution at different rotating rate and sweep rate of 5mV s -1. Since the OER is not controlled by mass transfer in this system, oxygen evolution reaction does not depend on the rotating speed of electrode S7

8 Figure S6. X-ray diffraction patterns of synthesized IrO 2 catalyst used in this study. The IrO 2 particle size was calculated as 3.0nm from XRD data using Scherrer s equation. S8