Methanol Tolerant FeTPP-Pt/C Co-catalysts for the Electroreduction of Oxygen

Chinese Chemical Letters Vol. 13, No.11, pp 1125- 1126, 20021125http://www.imm.ac.cn/jourmalccl.htmlMethanol Tolerant FeTPP-Pt/C Co-catalysts for the Electroreductionof OxygenXu Guang LI, Xiang Qing LIF, Wei XING', Xing Qiao WANG', Tian Hong LU'*'Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun 1300222Department of Chemistry, Jilin University, Changchun 130023Abstract: It was found for the first time that iron tetraphenylporphyrin (FeTPP)-Pt/C showed thegood activity for the electroreduction of oxygen and methanol tolerant ability. Their perfor-mances were related to the heat-treatment temperature.Keywords: FeTPP, Pt, oxygen reduction, methanol tolerant.Though direct methanol fuel cells have received much attention during the last thirtyyears', their performances are limited by several basic problems. One of them is thatmethanol in the anode will diffuse through the polymer electrolyte membrane to thecathode, causing the decrease in the electrocatalytic activity of Pt catalyst?, which is .usually used for electroreduction of oxygen. Thus, it is an important project to find anelectrocatalyst, which shows the good activity for oxygen reduction and methanoltolerant ability. In this paper, it was reported for the first time that FeTPP-Pt/C co-catalyst had the above ability.The electrochemical measurements were carried out with CHI602A potentiostat(CH Instrument Co.), Model 616 rotating disk electrode (EG&G PAR Co.). A Pt wireand a saturated calomel electrode were served as the counter electrode and the referenceelectrode, respectively. The working electrode was a glassy carbon electrode (0.196cm2). The FeTPP-Pt/C co-catalyst was obtained when FeTPP was adsorbed onplatinum supported on carbon black. The resulting FeTPP-Pt/C was heat-treated atvarious temperatures in Ar atmosphere for 2 hours. Then, 0.4 mL 5 wt% Nafion@solution (Aldrich Co.) and 5 mg FeTPP-PU/C catalyst were mixed. 5 u L suspensionwas placed on the surface of the working electrode and left to dry at room temperature.Figure 1A compares the polarization curves of Pu/C, FeTPP/C and FeTPP-Pt/C inO2- saturated 80 mL 0.5 mol/L H2SO4 without CH;OH and O2 saturated 0.5 mol/L H2SO4with 1 mol/L CH3OH. Figure 1A shows that the electrocatalytic activity of un-heat-treated FeTPP-PVC for oxygen reduction is worse than that of Pt/C in the absence ofmethanol, but better than that of FeTPP/C. In the presence of 1 mol/L CH,OH,electrocatalytic performance of FeTPP-Pt/C is better than that of Pt/C. For example,*E-mail: tianhonglu@ 263.net中国煤化工MHCNMH G.1126Xu Guang LI et al. .methanol oxidation causes the onset of cathodic current shifts cathodically by 0.07 V forFeTPP-PUC, while 0.13 V for Pu/C.The activity of heat- -treated FeTPP-Pt/C at 4509Cis better than that of Pt/C in the absence of methanol. In addition, the methanoloxidation has lttle effect on the performance of heat-treated FeTPP-Pt/C at 450°C(Figure 1B). The further experiments demonstrated that the methanol tolerant ability ofFeTPP-Pt/C increases with increasing the heat-treatment temperature. However, theactivity of FeTPP-Pt/C for oxygen reduction decreases gradually above 700°C. Theexperiment results indicated that heat-treated FeTPP-Pt/C at 450°C had the bettercatalytic activity and methanol tolerant ability simultaneously.The sublimation of FeTPP above 400°C will lead to re-dispersion of FeTPP overthe surface of co-catalysts, thus makes methanol difficult to access to the Pt atom due tothe steric hindrance. It may be the reason for methanol tolerant ability of FeTPP PVC.In addition, because both FeTPP and Pt are active for oxygen reduction, their interactionin FeTPP-_Pt/C may increase the electrocatalytic activity for oxygen reduction.Figure 1 Polarization curves(A) un-heat trated FeTPP PV/C(B) heat-treated FeTPP-Pt/C at 450°C200 -A200 FB多.00至-200-400-400上-6(-0.40.,40.8E/V vs.SCE(a) Pt/C, (b) FeTPP-Pt/C, (c) FeTPP/C in O-saturated 0.5 mol/L H2SO(a) Pt/C, (b) FeTPP-Pt/C in O-saturated 0.5 mol/L HSO with 1 mol/L CH,OH.Sweep rate: 10 mV/s, rotation rate: 1000 rpm, temperature: 25°C.AcknowledgmentsThe authors are grateful for the financial supports of 973 Program, National Science andTechnology Commission (G2000026408)， 863 Program, National Science and TechnologyCommission (2001AA320306), Natural Science Foundation, Jjilin Province (200005 10).ReferencesB. S. Baker, Hydrocarbon Fuel Cell Technology, Academic Press In.,. New York, 1965.2. A. Kuver, W. Vielstich, J. Power Sources, 1998, 74 (2), 211.Received 21 February, 2002中国煤化工MHCNMH G.