Confinement of Platinum Catalysts in Carbon Nanocontainers to Control the Durability in the Oxygen Reduction Reaction

Platinum and platinum alloys are widely used as catalysts for hydrogen fuel cells. However, several challenges need to be over come in order for Pt catalysts to reach their full potential. These include the high intrinsic costs, the fairly poor durability, wide nanoparticle size distributions, and a the lack of understanding of the precise nature of the contact between the catalyst and support materials.¹ Moreover carbon black, which is the most commonly used support material in fuel cells is thermo chemically unstable under acid conditions which drastically limits its use. Recently, carbon nanotubes (CNTs) and graphitised carbon nanofibres (GNFs), both of which have a number of exciting properties including; high specific surface areas, high electrical conductivity and relatively good stability in acid and alkaline media, have been proposed as alternative catalyst supports.² In addition, confinement of metal nanoparticles (NPs) inside these tubular structures potentially offers enhanced stability against sintering. As a consequence of this stabilisation the resultant catalysts will remain highly catalytically active for a significantly higher number of cycles making fuel cells financially more viable.³

In this study we have developed a series of GNF supported platinum composites for use as catalysts in the cathode side of the hydrogen fuel cell. Preformed free-standing platinum NPs (PtNPs) were deposited on either the external and internal surfaces of the GNFs using different conditions.⁴High resolution transmission electron microscopy (HRTEM) was used to characterise the composites, verifying the location of the PtNPs in each material (Figure1). The electrochemical active surface area of the composites materials, turn over numbers and the lifetime/stability of the materials was quantified using cyclic voltammetry, and the electrocatalytic activity of the catalyst towards the oxygen reduction reaction was assessed. It was found that depositing the PtNPs inside the GNFs (PtNPs@GNFs) rather than outside (PtNPs/GNF) resulted in a catalyst with higher catalytic activity, stability, and an increased electrochemical active surface area.

Figure 1: TEM images of the PtNPs@GNF (left) and Pt/GNFs (right) composites studied.

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2. L. Li, Yangchuan Xing, J.Electrochem. Soc., 2006, 153, 1823-1828.
3. G. A. Rance, W. A. Solomonsz, A. N. Khlobystov, Chem. Commun., 2013, 49, 1067.
4. A. La Torre, M. C. Gimenez-Lopez, M. W. Fay, G. A. Rance, W. A. Solomonsz, T. W. Chamberlain, P. D. Brown, A. N. Khlobystov, ACS Nano, 2012, 6, 2000-2007.