217th ECS Meeting, Abstract #589, © The Electrochemical Society
Tungsten/carbon nanotube supported platinum as cathode catalyst for proton exchange membrane fuel cell Doralice Meza1,2, Drew Higgins1, Leonardo.Salgado2, Zhongwei Chen1,* 1 Dept. of Chemical Engineering, Waterloo Institute of Nanotechnology, Waterloo Institute for Sustainable Energy, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1;
[email protected] 2 Dept. of Chemistry, Universidad Autonoma Metropolitana - Iztapalapa, Mexico City, 09340 The slow kinetics of oxygen reduction reaction is one of the major challenges of proton exchange membrane (PEM) fuel cells. Platinum has been the catalyst of choice for oxygen reduction reaction due its high catalytic activity. Nevertheless, its high cost impedes the widespread commercialization of fuel cells. Several attempts to decrease the amount of platinum loading have been done [1]. A common way of improving the catalytic activity of platinum electrodes is by increasing the electroactive area through the formation of well dispersed, small particles onto a support or matrix with high surface area. Further optimization of electrocatalyst materials has been obtained by the combination of platinum with other transitions metals such as W, Mo, Ru, Fe, Cr, Ti, Co and Ni [2,3], among others. Particularly, tungsten shows corrosion resistance in acidic media and has been used with platinum as anodic and cathodic materials in proton exchange membrane fuel cells [4,5]. It has been reported that Pt-W materials enhance the catalytic activity for different reactions such as carbon monoxide oxidation [6] and oxygen reduction [5]. Carbon nanotubes (CNT) have been studied as an electrocatalyst support due to their unique physical and chemical properties such as high surface area and good electronic conductivity. Tungsten/CNT composites have also been reported to be Pt catalyst supports for methanol or ethanol oxidation [7]. Nevertheless, incorporation of tungsten into Pt/W systems has been traditionally done by post-treatment of CNTs. Therefore, in this work, liquid chemical vapor deposition (LCVD) was proposed in order to synthesize tungsten/CNTs. Ethanol and ferrocene were respectively used as precursor and catalyst. The incorporation of tungsten was performed during the course of LCVD by sublimation of W(CO)6 salt, whereas platinum particles were deposited by an ethylene glycol (EG) reduction method.
Figure 1 ORR polarization curves for Pt/CNT (dashed line) and Pt-W/CNT (straight line) at 900 rpm in 0.1 M HClO4.
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The physical characterization of materials was carried out throughout X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The electrocatalytic performance upon oxygen reduction reaction (ORR) was assessed by means of cyclic voltammetry and rotating disk electrode techniques. Membrane electrode assembly tests were also conducted on a fuel cell station. Figure 1 shows oxygen reduction polarization curves for Pt/CNT and PtW/CNT in 0.1 M HClO4. A positive shift for half wave potential of 50 mV was obtained on PtW/CNT. To date this fact and based upon the hydrogen peroxide reduction properties of tungsten trioxide [8], PtWO3 would proceed as in a co-catalytic system where Pt reduces oxygen while WO3 reduces H2O2 generated during the oxygen reduction reaction.
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