Study of the effect of hydrogen on Pt supported Nanoporous Carbon derived from Polyfurfuryl alcohol
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Study of the effect of hydrogen on Pt supported Nanoporous Carbon derived from Polyfurfuryl alcohol Ramakrishnan Rajagopalan, Juan Coronado, Henry C. Foley and Albert Vannice Department of Chemical Engineering. Pennsylvania State University. University Park, Pa 16801,USA ABSTRACT Platinum supported on nanoporous carbon (NPC) is promising candidate for using as electrodes in proton exchange membrane fuel cells. Performance of the anode of a fuel cell is markedly influenced by the efficiency of the splitting of hydrogen atoms by platinum and the transference of the produced protons to the carbon support (spillover process). Consequently a better understanding of these elemental processes could prompt the improvement of the materials used. With this aim, a series of Pt/NPC samples varying the metallic content were studied by electron spin resonance (ESR) under controlled gas environment. This spectroscopic tool is especially suitable for the investigation of processes that involve transference of electrons. In the present case, all materials studied, including bare carbon, showed a very narrow signal (Hpp=1.5-3 gauss) at g=2.0028±0.0002 after activation in vacuum at 500ºC. In the case of the pure carbon and for the samples with lower platinum content (lower than 0.2 wt%) signals are significantly asymmetric, and their intensity is scarcely affected by the introduction of hydrogen up to 500ºC. In contrast the spin concentration experiences a significant increment when the samples with platinum loading comes in contact with hydrogen at temperatures in the 300-500ºC range. Although the centres originating these signals are located in the carbon matrix, the present results emphasize the importance of platinum for hydrogen activation and electron transference. INTRODUCTION Nanoporous carbon (NPC) possess enormous potential in the area of catalysis and gas separations due to their unique size and shape selectivity. The ease of formation and their high temperature stability facilitates the use of these carbons as templates for supporting catalytic materials such as Platinum and alkali metals [1-3]. The ability to form supported catalytic nanoporous membranes with this material expands the horizon of engineering applications that is not limited to gas separation and catalysis. One of the promising applications includes the use of platinum supported nanoporous carbon (Pt/NPC) membranes as electrodes in proton exchange membrane fuel cells (PEM). These materials present graphite-like domains that grant the necessary electrical conductivity along with the porous network, which allows the access of the gases to the catalytically active particles of platinum. Pt/NPC was prepared by pyrolyzing the suspension of platinum precursor dispersed in polyfurfuryl alcohol (PFA) under inert atmosphere. It has been demonstrated that extremely dispersed and uniform Pt clusters as small as 2 nm can be formed by pyrolysis of chloroplatinic acid suspended in polyfurfuryl alcohol [1,4]. The size of the platinum clusters showed very narrow d
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