Carbon supported platinum catalysts are widely used in PEMFC applications. The catalytic activity of the catalyst is strongly dependent on size and size distribution of the Pt nanoparticles deposited onto porous carbon support. In this study, the microwave-assisted synthesis method was used to study the effect of the Pt particle size and content (mass%) on the electrochemical activity of oxygen reduction reaction^1,2.

The Pt nanoparticles were deposited onto the carbon support using the microwave-assisted method^3–6. H₂PtCl₆×6H₂O (99.9%, Alfa Aesar) was dissolved in ethylene glycol (Riedel-de Haën), the carbon powder (commercial Vulcan XC72) was added and pH was regulated using NaOH. The synthesis mixture was heated in a commercial microwave oven until boiling two times. The product was filtered and thereafter washed with MilliQ⁺ water. Varying the pH level of the reaction media affected the Pt nanoparticle size and Pt content in the catalysts.

The X-ray diffraction and low temperature nitrogen sorption methods were used to characterize the catalysts materials.

The materials were electrochemically characterised using the rotating disk electrode technique as described by S. Kocha et. al ^7,8 in 0.1 M HClO₄ solution. The highest electrochemical surface area 93.8±13.3 m²g⁻¹ with mass activity of 436 mA mg⁻¹ and specific activity of 449 µA cm⁻² have been achieved.

The content of platinum in the catalyst was determined before and after the experiments using the electrochemical dissolution of platinum from the electrode in 6 M HCl solution. The average weight percentage of Pt in different catalyst materials was 17.3±4.1.

References

1. B. C. H. Steele and A. Heinzel, Nature, 414, 345–352 (2001) .

2. H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B Environ., 56, 9–35 (2005).

3. W. X. Chen, J. Y. Lee, and Z. Liu, Chem. Commun., 2588–2589 (2002).

4. X. Li, W.-X. Chen, J. Zhao, W. Xing, and Z.-D. Xu, Carbon, 43, 2168–2174 (2005).

5. Z. Liu, J. Y. Lee, W. Chen, M. Han, and L. M. Gan, Langmuir, 20, 181–187 (2004).

6. S. Horikoshi and N. Serpone, Eds., Microwaves in nanoparticle Synthesis: Fundamentals and Applications, WILEY-VCH Verlag GmbH & Co KGaA, (2013).

7. K. Shinozaki, J. W. Zack, R. M. Richards, B. S. Pivovar, and S. S. Kocha, J. Electrochem. Soc., 162, F1144–F1158 (2015).

8. K. Shinozaki, J. W. Zack, S. Pylypenko, B. S. Pivovar, and S. S. Kocha, J. Electrochem. Soc., 162, F1384–F1396 (2015).

Acknowledgements This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT55, Estonian Centre of Excellence Projects No. 2014-2020.4.01.15-0011 and 3.20101.11-0030.