Nanoparticle catalysts for proton exchange membrane fuel cells : a study of surfactant effects on dispersion and catalysis

• Main Author: Newton, Jill Elizabeth
• Published: University of Birmingham 2014
• Subjects: 660; TP Chemical technology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633343

Minimisation of Pt loading in proton exchange membrane fuel cells (PEMFCs) is important because Pt is expensive and its supply is limited. Nanoparticle aggregation is a problem because aggregated nanoparticles have a lower surface area and so exhibit lower mass activity than well dispersed nanoparticles. In the present work platinum nanoparticles were successfully prepared, by an aqueous colloidal route, using tetradecyltrimethylammonium bromide (TTAB) and nonylphenolethoxylate (NP9). Such organic molecules which adsorb on the surface of nanoparticles are generally regarded as undesirable species which block catalytic sites and slow reaction kinetics. However, removal processes cause particle aggregation. Here the performance of catalysts was studied using a rotating ring disc electrode (RRDE), without extensive removal of surfactant. Nanoparticles prepared using NP9 surfactant showed catalytic activity for the oxygen reduction reaction (ORR) similar to the commercial catalyst (TKK) but TTAB had a strong poisoning effect. Finally the performance of the Pt+NP9 nanoparticles was compared with the commercial catalyst (TKK) using single cell MEA testing. The main difference in performance was in the mass transport region of the polarisation curve. The conclusion was that surfactant stabilization of Pt nanoparticles is important to fuel cell performance, while subtle effects of molecular structure on catalytic activity require more investigation.