Effect of Rotation Rate on the Formation of Platinum-modified Polyaniline Film and Electrocatalytic

Chinese Chemical Letters Vol. 15, No.1, pp115- 117, 200415htp://ww.imm.ac. cn/journal/ccl.htmlEffect of Rotation Rate on the Formation of Platinum-modifiedPolyaniline Film and Electrocatalytic Oxidation of MethanolQiu Hong LI', Lin NIUl*, Chang Qiao ZHANG' , Feng Hua WEr,Hu ZHANG''School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100Shandong Analysis and Test Center, Jinan 250014Abstract: The oxidation of methanol was investigated on platinum- modifed polyaniline electrode.Changes in the electrode rotation rates ( 2 ) during platinum electrodeposition remarkably affectthe formation and distribution of platinum in the polymer matrix and consequently lead to differentcurrents of methanol oxidation. The results show that platinum loading is proportional to rotationrates 0Keywords: Platinum- modified polyaniline electrode, electrode rotation rate, methanol oxidation,electrocatalytic activity.The preparation of highly active electrodes is of considerable interest to theelectrocatalytic oxidation of methanol. The routine method is to disperse, at molecularlevel, electrocatalytic materials, such as platinum and platinum-based alloys in theelectron conductive polymers.Polyaniline (PAni)， which is easy to synthesize iaqueous medium and chemically stable in air, is a very interesting support material.Many factors, such as polymerization procedure, polymerization potential, dispersitydegree or particle size of platinum metals, will influence the activity of electrode. Thoughmuch work has been done on the electrocatalytic activities of platinum-modifiedpolyaniline electrodes for the methanol oxidation reaction' , few researchers havedevoted to study the dependence of platinum loading and dispersity on the electroderotation during the platinum electrodeposition. The aim of the present work is toexplore the effect of electrode rotation rates on the formation and ditribution of platinumparticles in the polymer films and the subsequent methanol oxidation.The Electrochemical measurements were performed with CHI650A Potentiostat /Galvanostat and ATA-1A rotating electrode apparatus. A glassy carbon (GC) rotatingdisc (geometric area 0. 1256 cm2 ) was used as working electrode. The counter electrodewas a Pt plate and reference electrode was a saturated calomel electrode (SCE). Themodification of the disk electrodes was performed in two steps: (a) Electropolymeri-zation of aniline by potential cycling (15 cycles at a scan rate of 50 mV/s) between -0.2and 0.9 V (vs. SCE) in aqueous solution containing 0.1 mol/L aniline + 0.5 mol/L H2SO4.E-mail: lniu@sdu.edu.cn中国煤化工MHCNMH G.116Qiu Hong LI et al.The thickness of the polymer films was estimated to be 0.6 imd. (b) Deposition ofplatinum particles into the PAni film by electroreduction of chloroplatinic acid (0.003mol/L) in 0.5 mol/L sulfuric acid with different electrode rotation rates. Eachelectroreduction step involved 25 potential cycles in the range from -0.1 to 0.8 V (scan .rate= 50 mV/s). Cyclic voltammetry was used to evaluate the electrocatalytic effect ofthe platinum-modified polyaniline electrode, with different platinum loadings, on themethanol oxidation in 0.1 mol/L methanol + 0.5 mol/L H2SO4 solutions. Allexperiments were carried out at 25土1°C.Results and DiscussionThe dependence of platinum loading on rotation rates 2 12 is given in Figure 1. Asshown in Figure 1, platinum loading is proportional to 2 , showing that rotation ratehas a great effect on platinum loading. The amount of loaded platinum particles wasdetermined from the charge passed during the loading step by assuming that the reductionof Pt4+ to Pt0 is 100% efficient?. When the rotation rate increases from 0 to 1500 r/min,the amount of platinum deposits increases from 0.14 to 1.42 mg/cm2 (geometric area).Figure 1 Plot of platinum loading W vs. rotation rates s21"2 during platinum depo-sition on a polyaniline-covered glassy carbon rotating disc electrode.2.8-三.4-0.0-0 203(402 "1(r/min)“Figure 2 shows the effect of rotation rate of platinum electrodeposition on thecyclic voltammograms of methanol oxidation. From the CVs, one can see that themethanol oxidation peaks rise with the increase of rotation rates of platinumelectrodeposition.One reason may be that with the increase of rotation rates, theplatinum loading and particle size grow gradually， which leads to a higherelectrocatalytic activity of the electrode. Another reason probably is that platinum canbe dispersed sufficiently into the PAni polymer with the increase of rotation rates.Highly dispersed platinum is less susceptible to poison. The poison of the catalytic sitecaused by the fixation of intermediate species, which produced during methanoloxidation, is decreased*. Therefore, the catalytic activity of the electrode increases.中国煤化工YHCNMH G.Platinum-Modified Polyaniline Film117In summary, the electrode modified by platinum particles dispersed inside of thepolyaniline film shows high activity with respect to methanol oxidation. Rotation rateof electrode has a great effect on the deposition of platinum. With the increase ofrotation rates of platinum deposition, platinum loading increases as a function of2 1/2.Moreover, platinum particles may be dispersed into the polymer homogeneously with theincrease of rotation rates. More intensive work in this respect is in progress.Figure2 Cyclic voltammograms of methanol oxidation (Scan rate: 5 mV/ s) rotation rateduring platinum deposition:a-0, b- 500, c- 1000, d- 1500r/ min.2F.0.8-.4-.2.0-.2L0.0.8E/V vs. SCEAcknowledgmentsThis project was supported by the Research Foundation for Exellent Middle -aged andYoung Scientists of Shandong Province (Project No.9937) and the Research Foundationfor Returming Scholars of Ministry of Education of China.ReferencesM. J. Croissant, T. Napporn, J.M. Le ger , C. Lamy, Electrochim. Acta, 1998, 43, 2447.K. Bouzek, K. M. Mangold, K. Juttner, J. Appl. Electrochem, 2001, 31, 501A.A. Mikhaylova, E.B. Molodkina, O.A. Khazova, V.S. Bagotzky, J. Electoaanal. Chem,2001, 509, 119.A. Kelaidopoulou, A. Papoutsis, G. Kokkinidis, J. Appl. Electrochem, 1999, 29, 101.Received 20 December, 2002中国煤化工MHCNMH G.