ИСТИНА

Significant improvements in power density and costs of both high and low temperature polymer electrolyte fuel cells (PEFC) have been achieved during the last two decades [1,2]. Nevertheless enhancing durability and lifetime of membrane and electrode materials remains a critical issue for PEFC commercialization. A significant portion of the performance losses is due to the loss of electrochemical surface area of Pt catalyst with time. Dissolution of Pt nanoparticles at the cathode side is considered as one of the main mechanisms of electrocatalyst degradation [3,4]. However the role of operating conditions and their influence on the mechanisms of Pt dissolution are still not well understood. To the best of our knowledge there are no data on influence of polymers on the mechanisms of Pt dissolution. In the present work we study the influence of AB-polybenzimidazole (ABPBI) on dissolution of Pt nanoparticles in hot phosphoric acid (PA). ABPBI in crosslinked form is widely used as a membrane material and is also often added into the catalyst layers of high temperature PEFC as a binder. The experiments have been performed in a conventional three electrode cell with RHE, the concentration of Pt dissolved in PA has been measured by means of atomic absorption spectroscopy. We have found that the presence of ABPBI dissolved in PA results in a significant (about 2 orders of magnitude) increase of the rate of Pt dissolution under potentiostatic conditions at potentials corresponding to open circuit. We suppose that the presence of PBI in the solution affects both electrochemical and chemical pathways of Pt dissolution. The formation of complexes of the ABPBI with Pt likely shifts the equilibrium potential of the Pt/Pt(II) system to somewhat lower values, which results in accelerated electrochemical dissolution of Pt. It is also possible that the chemical dissolution of Pt oxides is accelerated as well due to the increased solubility of Pt oxide species in the presence of ABPBI. Due to Ostwald ripening accelerated dissolution of Pt in the presence of ABPBI affects the particle radius distribution and leads to an increased average nanoparticle size and, consequently, lower electrochemical surface area of Pt catalyst. We conclude that in order to prolong lifetime of Pt based electrocatalysts in high temperature PEFC one should minimize contact between Pt and PBI and avoid using PBI as a binder in cathode catalyst layers. M.S.K. and M.O.G. gratefully acknowledge the financial support from Skolkovo Institute of Science and Technology. 1. Stumper, J., Stone, C. J. // J. Power Sources 176 (2008) 468-476. 2. Chandan, A., Hattenberger, M., El-kharouf, A., Du, S., Dhir, A., Self, V., Pollet, B. G., Ingram, A., Bujalski, W. // J. Power Sources 231 (2013) 264-278. 3. Rinaldo, S. G., Stumper, J., Eikerling, M. // J. Phys. Chem. C 114 (2010) 5773-5785. 4. Shao-Horn, Y., Sheng, W. C., Chen, S., Ferreira, P. J., Holby, E. F., Morgan, D. // Top Catal 46 (2007) 285–305.