Supporting Information

Accelerated Testing of Polymer Electrolyte Membranes under Open-

Circuit Voltage Conditions for Durable Proton Exchange Membrane Fuel

Cells

Myungseong Hana,b, Yong-Gun Shula,b, Hyejin Leea, Dongwon Shina, Byungchan Baea,c,*

aFuel Cell Laboratory, Korea Institute of Energy Research, Daejeon, South Korea

bDepartment of Chemical and Biomolecular Engineering, Yonsei University, 262 Seongsanno,

Seodaemun-gu, Seoul, South Korea

cRenewable Energy Engineering, University of Science & Technology (UST), 217, Gajeong, Yuseong,

Daejeon, South Korea

*Corresponding author. Tel: +82 42 8603586 Fax: +82 42 8603104

E-mail address: bcbae@kier.re.kr

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Experimental

Sulfonated poly(ether sulfone) (SPES50) (50% sulfonation) was purchased from Yanjin Chemical (China) (Fig.

S1). Nafion NRE212 and HP membranes (DuPont) were used as received. The SPES50 membranes were

prepared by the solution-casting method. SPES50 was dissolved in an organic solvent (7 mL, 10 wt% in

dimethyl sulfoxide) and was poured on a clean glass plate. The glass plate was dried on a hot plate at 70 °C for

12 h, and then in a vacuum oven at 80 °C for 6 h to produce a homogeneous membrane (50-μm thick). The

membrane was acidified using 5 M HCl for 8 h at 80 °C and deionized water for 4 h.

The fuel cell electrodes were prepared as follows. A metal catalyst layer (ionomer: 20 wt% against supported

catalyst) was prepared using the decal transfer method. A platinum-supported catalyst (HISPEC4000, Johnson

Matthey Catalysts) and Nafion ionomer were mixed to form a slurry, which was coated onto the polymeric

substrate. The dried catalyst layer was thermally transferred to the membranes by compression for 4 min at 140

°C. Finally, an MEA (25 cm2 electrode area) was obtained by edge sealing. Pt was used for the anode and

cathode catalysts (loading amounts of ~0.20 mg·cm-2).

The OCV of each cell was observed using an potentiostat (ZIVE SP2, WonATech, Korea), and the high-

frequency resistance (HFR) was monitored using a 1-kHz miliometer (Hioki) every 24 h. The cell was operated

at 90 °C and 30% relative humidity (RH) under atmospheric conditions (NEDO conditions). To evaluate the

status of the electrode layer, CVs, and LSVs were measured using a potentiostat (HCP-803, Bio-Logic Science

Instruments, France). Prior to the potential sweep, the potential was stabilized by purging the cathode with N2

gas (500 mL·min-1, 90 °C, 30% RH), while H2 gas was supplied to the anode (200 mL·min-1, 90 °C, 30% RH).

Then, the potential was swept from 0.05–1.2 V (scan rate of 50 mV·s -1). The ECSA was determined from the

hydrogen desorption charge in the positive potential scan (ΔQH° = 0.21 mC·cm-2), adopted conventionally for

clean polycrystalline platinum.

For the LSV measurement, H2 (200 mL·min-1, 90 °C, 30% RH) and N2 (500 mL·min-1, 90 °C, 30% RH) were

supplied to the anode and cathode, respectively. After stabilizing the potential for 10 s, the potential was swept

from 0.1–0.6 V (scan rate of 1.0 mV·s-1). The crossover current was obtained from the y-intercept of the

extrapolated current density from 0.4–0.5 V, and the electronic resistance (short-circuit resistance) was

determined from the inverse of the slope.

2

(a)

(b)

Figure S1. Chemical structure of (a) Nafion and (b) SPES50.

3

Figure S2. Initial cyclic voltammograms of NRE212, Nafion HP, and SPES50 of cathode at 90 °C and

30% RH.

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Figure S3. Initial linear sweep voltammograms of NRE212, Nafion HP, and SPES50 of cathode at 90

°C and 30% RH.

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