Inhibiting Effects of Nafion on ORR Catalyzed By Precious and Non-Precious Electrocatalysts Supported on Carbon

Nafion has been an ionomer of choice in polymer electrolyte fuel cells (PEFCs) for three decades.¹ However, recent research studies demonstrate that the polymer has a number of undesired properties. One of such properties is its ability to restructure at the catalyst surface, which may lead to a partial blocking of the catalyst surface and thus an inhibition of the desired electrochemical reactions, i.e., oxygen reduction and hydrogen oxidation. While a simple evidence for the blocking was presented for ideal Pt/Nafion interfaces,^2-5quantitative evaluation of such effects is much more difficult for highly dispersed catalysts, such as carbon supported Pt.

                In this work, we will present results of our recent rotating ring disk electrode study on the inhibiting effects of Nafion on the electrocatalysis of oxygen reduction by carbon supported Pt and transition metal macrocycles. We will demonstrate that carbon plays an active role in the ORR inhibition and that the effects are especially strong for the non-precious catalysts (Fig. 1).

Acknowledgement

The financial support from the University of California (grant 12-LR-237440) is gratefully acknowledged.

References

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2)       J. Chlistunoff, F. Uribe, B. Pivovar, ECS Trans., 1,137-146 (2006).

3)       J. Chlistunoff, F. Uribe, B. Pivovar, ECS Trans. 2, 37-46, (2006).

4)       J. Chlistunoff, B. Pivovar, ECS Trans., 11, 1115-1125 (2007).

5)       D. L. Wood, J. Chlistunoff, J. Majewski, R. L. Borup, J. Am. Chem. Soc., 131, 18096-18104 (2009).

Fig. 1. The effect of Nafion on ORR catalyzed by carbon (XC72) supported cobalt phthalocyanine (CoPC). Scan rate 10 mV s^‑1. Rotation rate 400 rpm. Catalyst ink composition: 46.5 mg XC72; 0.8 mg CoPC; 8 cm³ isopropanol; 41.9 μl 5% Nafion (solid line); 83.9 μl 5% Nafion (dotted line). Catalyst loading 0.1 mg (for XC72).