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# Gas Diffusion Electrode With Large Amounts of Gas Diffusion Channel Using Hydrophobic Carbon Fiber: For Oxygen Reduction Reaction at Gas/Liquid Interfaces

[+] Author and Article Information

Department of Chemical System Engineering,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan;
Department of Materials and Life Science,
Faculty of Science and Technology,
Seikei University,
3-3-1 Kichijoji-kitamachi,
Musashino-shi, Tokyo 180-8633, Japan

Pantira Privatananupunt

Department of Chemical System Engineering,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
e-mail: myosinsama@gmail.com

Toshiyuki Iwasaki

Department of Chemical System Engineering,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
e-mail: awk104@gmail.com

Ryuji Kikuchi

Department of Chemical System Engineering,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
e-mail: rkikuchi@chemsys.t.u-tokyo.ac.jp

1Corresponding author.

Manuscript received January 27, 2017; final manuscript received April 14, 2017; published online May 2, 2017. Assoc. Editor: Dirk Henkensmeier.

J. Electrochem. En. Conv. Stor. 14(2), 020903 (May 02, 2017) (9 pages) Paper No: JEECS-17-1014; doi: 10.1115/1.4036507 History: Received January 27, 2017; Revised April 14, 2017

## Abstract

For a gas diffusion cathode for oxygen reduction reaction (ORR) in aqueous alkaline electrolyte, it is important to create networks for O2 gas diffusion, electronic conduction, and liquid-phase OH transport in the cathode at once. In this study, we succeeded to fabricate a promising cathode using hydrophobic vapor grown carbon fibers (VGCF-Xs), instead of hydrophobic carbon blacks (CBs), as additives to its active layer (AL). Mercury porosimetry, as well as electrochemical impedance spectroscopy, showed that porosity of the cathode gradually increased with increasing the amount of the carbon fibers. In other words, addition of larger amount of the carbon fibers creates better O2 gas diffusion channels. Also, the activation polarization resistance for the ORR increased as the carbon fibers' amount from 0 to 0.03–0.04 g and then dropped. In consequence, the cathode with 0.03 g of the carbon fibers exhibited the highest ORR performance among the prepared cathodes.

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## Figures

Fig. 1

Schematic image of (a) gas diffusion electrode structure, (b) procedure for gas diffusion electrode fabrication, (c) apparatus for electrochemical measurement, (d) preparation of working electrode, and (e) apparatus for cyclic voltammetry measurement

Fig. 2

Equivalent circuit used in this study; Rs: ohmic resistance, R1: activation resistance, R2: diffusion resistance, and CPE: constant phase element

Fig. 3

Transmission electron microscopy image of Pt/CB

Fig. 4

Scanning electron microscopy images of AL surface of (a) CF3 and (b) CF6. Scale: (from left to right) ×30 k and ×150 k.

Fig. 5

Pore size distribution of several types of GDEs obtained by Hg porosimetry: (a) NC, (b) CF1, (c) CF3, (d) CF6, (e), CB6, and (f) No AL. Pressure: 0–4000 atm.

Fig. 6

Influence of VGCF-X or hydrophobic CB presence in AL on (a) specific volume of secondary pores and (b) porosity of AL. Detail information is in Table 2. “No AL” sample is a GDE without AL.

Fig. 7

I–V curves of NC, CF6, and CB6. All experiments were conducted under O2 partial pressure = 1.0 atm at 70 °C. Sweep rate: 5 mV s−1.

Fig. 8

Nyquist plots of (a) NC, (b) CF6, and (c) CB6. All experiments were conducted under O2 partial pressure = 1.0 atm at 70 °C.

Fig. 10

I–V curves of (a) NC, (b) CF1, (c) CF3, and (d) CF6. All experiments were conducted under O2 partial pressure = 1.0, 0.6, and 0.2 atm at 70 °C. Sweep rate: 5 mV s−1.

Fig. 11

Nyquist plots of CF6. All experiments were conducted under O2 partial pressure = (a) and (d) 1.0, (b) and (e) 0.6, and (c) 0.2 atm at 70 °C.

Fig. 9

I–V curves of CF1, CF3, CF4, and CF6. All experiments were conducted under O2 partial pressure = 1.0 atm at 70 °C. Sweep rate: 5 mV s−1.

Fig. 12

Effect of VGCF-X amount in the GDEs on (•) current density (at ΔE=−0.5 V), (◻) activation resistance, and (△) diffusion resistance. All experiments were conducted under O2 partial pressure = (a) 0.6 atm and (b) 1.0 atm at 70 °C. The raw data were summarized in Table 3.

Fig. 13

Cyclic voltammetry for NC, CF3, CF6, and CB6

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