Carbon nanotubes with Pt–Ru catalyst for methanol fuel cell

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Abstract

Multiwalled carbon nanotubes (NTs) have been used as an attractive support of catalytic metallic particles for methanol electrooxidation in acidic medium. Pt–Ru (50:50) nanoparticles were deposited on the different type of nanotubular materials to select the best support and to estimate the efficiency of CH3OH oxidation. Pt–Ru supported on NTs graphitized at 2500 °C supply the optimal voltage/current characteristics with a maximum current load of 2.7 A/g. Mesoporous network of nanotubes combined with their excellent conducting properties allows a quick transport and easy accessibility of the reagent molecules to the catalytic sites of electrode interface giving a good performance of methanol anode.

Introduction

The direct methanol fuel cell is one of the most promising energy sources for the nearest future [1], [2], [3]. Since methanol oxidation in acidic medium requires the application of noble metals, generally platinum and/or its binary alloys, an intensive research is devoted to decrease the catalyst loading [4], [5], [6], [7], [8], [9]. The kinetics and total efficiency of the process strongly depend on the catalyst dispersion, which is quite often determined by the support. In this paper, multiwalled carbon nanotubes (NTs) are used as catalyst support. Attractive properties of nanotubes related with their good electrical conductivity, entanglement and high resiliency have been demonstrated in other electrochemical energy storage systems, e.g., supercapacitors [10], [11], [12]. Some investigations have already been performed with an application of carbon nanotubes as a promising catalyst support for cathodic and anodic reactions in fuel cell [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. However, there is a lack of correlation of the nanotubular texture and/or structure with an electrochemical behavior.

Our target is to investigate various nanotubes as a catalyst support and to select the optimal type of NTs for Pt–Ru particles used in the methanol anode.

Section snippets

Experimental

Binary Pt–Ru (50:50) catalyst particles from Alfa Aesar Johnson Matthey have been deposited on different kinds of nanotubes. To ensure the same distribution and amount of catalyst and to pronounce only effect of a support, the deposition of catalyst particles from ethanol suspension was applied for all the nanotubular materials. We used either entangled NTs prepared by catalytic decomposition of acetylene on a CoxMg(1  x)O solid solution catalyst [24] or stiff nanotubes obtained by propylene

Results and discussion

For all the nanotubular carbon samples, the nitrogen adsorption/desorption isotherms reveal a mesoporous character (IV type isotherm) due to the entanglement and/or the presence of the central canal. The BET specific surface area of the CoxMg(1  x)O catalytically grown nanotubes is 290 m2 g−1 and it diminishes to 159 m2 g−1 after annealing whereas KOH activation causes its enhancement to 402 m2 g−1. For the nanotubes obtained by the template technique it reaches only 15 m2 g−1. Transmission electron

Conclusion

One can summarize that nanotubular materials fulfil perfectly the conditions of conducting and well accessible mesoporous network for catalytic particles. Pt–Ru particles of 2–3 nm size were equally deposited on different nanotubular supports. The selection of optimal support is crucial for a performance of methanol anode and it was clearly shown, that the best results of methanol oxidation are obtained for graphitized carbon nanotubes with deposited catalyst. This high electrocatalytic activity

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