In situ time-resolved FTIRS study of adsorption and oxidation of ethylene glycol on Pt(100) electrod

ARTICL .ESChinese Science Bulletin 2005 Vol. 50 No.18 1995- -1998sorption of EG may occur due to the strong interactionbetween EG and Pt surface, resulting in formation of ad-In situ time-resolved FTIRSsorbed CO species and other strongly bound adsorbates,study of adsorption andwhich empoisons Pt surface and causes the so-called“self-poisoning”phenomenon. However, these studiesoxidation of ethylene glycol onwere focused mainly on surface structure effects of Ptelectrodes and on the reaction mechanism by determiningPt( 100) electrodeintermediates and products involved in EG electrocatalyticoxidation using different methods, such as chromatogra-phy2, in situ FTIR spectrosopyl'-010.1, and differ-FAN Youjun, ZHOU Zhiyou, FAN Chunjie,ential electrochemical mass spectroscopy"", and the sur-ZHEN Chunhua, CHEN Shengpei & SUN Shigangface processes and kinetics of EG oxidation were lessState Key Laboratory of Physical Chemistry of Solid Surfaces, Deparment of Chemistry, Xiamen University, Xiamen 36 1005, ChinaCorrespondence should be addressed to Sun Shigang (email: sgsun@level. In the present paper, the dissociative adsorption andxmu.edu.cn)oxidation of EG on Pt(100) surface are investigated by inxmu.situ time-resolved FTIR reflection spectroscopy, and newAbstract Adsorption and oxidation of ethylene glycolinformation of EG reaction kinetics was obtained.(EG) on Pt(100) electrode were studied by in situ time-1Experimentalresolved FTIRS (TRFTIRS). The TRFTIR spectra recordedat 0.10 V ilustrate that an IR band appears near 2050 em-1In situ time-resolved FTIR spectroscopy experimentsat t > 5 s, corresponding to linearly bonded CO formed inwere carried out on a Nexus 870 FTIR apparatus (Nicolet)dissociative adsorption of EG. The TRFTIR results haveequipped with a liquid nitrogen cooled MCT-A detector.confirmed also that CO species are distributed uniformly on10 interferograms were collected and co-added into eachPt(100) surface. Another band appears near 2342 cm-1 atspectrum of spectral resolution 16 cm~ . The resultingt > 70 s, associating with IR absorption of CO2 produced inthe direct oxidation of EG. With the increase of electrodespectrum is calculated as AR/R=(RE, - RE, )1RE, , wherepotential, the direct oxidation of EG becomes gradually themain reaction. When the potential is above 0.40 V, the oxida-RE，and RE, are single-beam spectra recorded at E andtion of EG occurs mainly via the reactive intermediates, i.e.E, respectively. A saturated calomel electrode (SCE) wasspecies containing -COOH determined by in situ TRFTIRS.used as reference electrode. Before each measurement theKeywords: ethyene glycol, P(100) eletrode, dssociative adsorption Pt(100) electrode was annealed in a hydrogen-oxygenand oxidation, in situ time-resolved FTIR spectroscopy.flame, quenched with super pure water and transferredDOI: 10.1360/982004-540into electrochemical cell under protection of a droplet ofpure water. The solutions were prepared using MilliporeMetal single crystal planes provide model electrocata- water (18.0 MQ cm) provided from a Milli-Q Lablysts of well-defined surface structure, and play an impor-apparatus (Nihon Millipore), super pure H2SO4 and ethyl-tant role in fundamental studies of electrocatalysis. EthyI- ene glycol of analytical grade (both from Shanghaiene glycol (EG) has attracted considerable interests inChemicals, Inc., China). All measurements were carriedboth basic studies and applications in direct fuel cells, out at around 20"C.since its complete oxidation transfers 10 electrons. In the2 Results and discussionstrong acid environment of proton exchange membranefuel cell (PEMFC), the sole stable and most active metalOur previous studies 181 ilustrated that the average ratecatalyst for the electro-oxidation of alcohols is platinum'(σ ) of dissociative adsorption of EG on Pt(100) electrodeExtensive efforts have been devoted to investigating elec-varies with adsorption potential Ead following a volcano-trochemical adsorption and oxidation properties of EG ontype distribution. The maximum of σ (σmax ) is locatedPt elctrodes with different suface structures2- 17. Theresults demonstrated that the electrocatalytic oxidation of no matter whether Ead decreases or increases gradually. σEG on Pt electrode occurred via a dual path reactiontends towards zero when the adsorption potential is belowmechanism, and its oxidation includes a set of consecutive-0.22 V or above 0.40 V.and parallel steps yielding several C1- and C2-produ-In situ time-resalved FTIR snectra (TRFTIRS) obtained:ts- 6.9. The oxidation route of EG proceeding withouton Pt(100) eld中国煤化工40 and 0.90 v in .C-C bond cleavage in acidic solutions includes consecu-0.1 mol L'YHC N M H Glution are showntive, two-electron transferring processes that yield somein Fig. l(a)-(d). We can see from Fig. 1(a) that a nega-intermediates, such as glycolaldehyde, glyoxal, glycolicacid, glyoxylate and oxalic acids, and the final product is .tive going band near 2050 cm- ! starts to appear in theCO2 In parallel to the above route, the disciative ad- spectrum at 1> 5 s, corresponding to linearly bonded COChinese Science Bulletin Vol. 50 No. 18 September 20051995ARTICLES(@)(b- 257.4s|重220020002400v/cm-'v/cm~'(C)d)205.4s205.7s6.23 s6.23 s .2.08 s2.08s1500v/cm-1Fig. 1. In situ time-resolved FTIR spectra obtained for Pt( 100) electrode in 0.1molLl EG + 0.1 mol L' H2SO4 solution with E at-0.22 V and Er at (a) 0.10 V, (b) 0.25 V, (c) 0.40 V, (d) 0.90 V.(CO) derived from dissociative. adsorption of EG on dized at 0.10 V where is located the maximum value ofPt(100) electrode at E2 = 0.10 Vl23.0. The intensity of the0 in itsvolcano-type distribution, and ilustrates theband increases progressively with time and attains almostcompetitive reaction with EG dissociative adsorption. Fig.a constant value att> 100 s. The negative going monopo- 2(a) shows the variation of the integration intensity oflar band and its variation indicate that the dissociative COL and CO2 bands with ↑on Pr(100) surface for E2=adsorption of EG on Pt(100) electrode at E = -0.22 V has0.10 V. We can see that the formation of COL on Pt(100)not occurred (otherwise a bipolar band will appear), andsurface in EG dissociative adsorption is obviously moreCOL species were formed exclusively at 0.10 V. The in-significant than the production of CO2 species in EG di-tensity of the band increases progressively with t, indicat-rect oxidation.ing that the quantity of COL increases gradually and it isIn Fig. 1(b) (Ez = 0.25 V), we can observe two similaraccumulated on Pt(100) surface. The band center (Vco, ) IR bands, namely, COr band at about 2050 cm-' and CO2shifts positively with time from 2042 cm-' (t= 7.8 s) toband around 2342 cm l. The intensity of CO band still2054 cm-' (t = 257.4 s), which is apparently caused by theincreases with increasing t and rapidly attains a stableincrease of COL coverage, and demonstrates that the COLconstant value, and in the initial stage of reaction the bandspecies are distributed uniformly on Pt(100) surfacecenter (Vco, ) also shifts positively with increasing t. Inwithout the formation of island. At the same time, a smallcontrast to the中国煤化工2 band appears innegative going band near 2342 cm-1 appears whent> 70s，the initial staYHCNMHG! increases fastercorresponding to the asymmetry stretching of CO2 that is with increasinThe variation ofthe final product of EG direct oxidation3- )!. The intensityintegration intensity of COL and CO2 bands with t at thisof this band increases progressively with t. The appear- potential is shown in Fig. 2(b). We can see that in the re-ance of CO2 band indicates that EG can be directly oxi-corded time window, the intensity of CO2 band increases1996Chinese Science Bulletin Vol. 50 No. 18 September 2005ARTICL ESlinearly and quickly with increasing t, and the variation of CO2 bands is gradually increased with increasing 1, and is .COL band intensity with t is similar to that of E2= 0.10 V. apparently larger than that measured at E2 = 0.25 V. ThisWe can see also that when t is larger than 60 s, the inten-may indicate that the rate of EG direct oxidation increasessity of CO2 band becomes stronger than that of the COLsignificantly at E2 = 0.40 V, accordingly, the production ofbandintermediates containing -COOH and CO2 in EG oxida-When E2= 0.40 V (Fig. 1()), the number of IR bands tion on Pt(100) is fast at this potential. We can also seeis increased and all bands are negatively going. Except the that the intensity of IR bands near 1100 and 1059 cm-' isCOL and CO2 bands, the assignment of other bands is asgradually increased with increasing t, which may be at-follows: the bands near 1740 and 1230 cm~' may be at- tributed to the consumption of H2O in the thin-layer solu-tributed to IR absorption of -COOH groups'*; the band tion involved in EG oxidation. In addition, the COL bandnear 1100 cm~' can be assigned to the stretching vibrationcan be hardly observed in the spectra, which may be at-of SO4- anions'19); the band near 1059 cm can be astributed to three aspects: (1) The rate of EG dissociativecribed to C-0 stretching of the primary alcohol4 .adsorption is very small at this potential8; (2) the ad-Among these bands, the intensity of the - COOH and the sorbed Co derived from EG dssociative adsorption canbe oxidized, which decreases the possibility of COad ac-cumulation on Pt( 100) surface; (3) the competition occurs(aCO.●between dissociative adsorption and direction oxidation ofEG, the ltter takes place via the reactive intermediates, i.e.1.6-species containing - COOH determined by in situTRFTIRS. With further increase of sample potential E2.2-(Fig. 1(), the intensity of the above IR bands is increased rapidly with increasing t, which can be clearly0.8-seen from in situ TRFTIR spectra of different E2 but at thesame reaction time (t = 60 s) shown in Fig. 3. From the .variation of integration intensity of CO2 band with t at E2100 150 200 250= 0.75 V given in Fig. 2(c), we can see that when t is .longer than 100 s, the quantity of CO2 produced by EG(boxidation approaches to a stable value. At this potential no5COad species can be detected by in situ TRFTIRS.Eg/NI 0.902+0.751COL0.600-0.5050 100 150 200 2500.400.32070.25(CCO2x200015000+v/cm-'Fig. 3. In situ time-resolved FTIR Spectra recorded on Pt(100) elec-trode for reaction timet= 60s in 0.1molL' EG+ 0.1 mol L H2SO4solution with E22 Y and varving R.∩100.18, 0.25, 0.32, 0.40,0.50, 0.60, 0.75,中国煤化工50100150200t/s3 Conclusid.FYHCNMHGIn the present paper, the adsorption and oxidation ofFig. 2. Comparison of variation of integration intensity () of CO, andethylene glycol (EG) on Pt(100) electrode were studied byCO2 band versus reaction time1. (a) E2=0.10 V;(b)E2=0.25 V;(c)E2=in situ time-resolved FTIRS. The results demonstrated that0.75 V.Chinese Science Bulletin Vol. 50 No. 18 September 20051997ARTICL .ESa negative going band near 2050 cm-' corresponding toformations under steady-state experimental conditions at a plati-linearly bonded CO (CO1) formed mainly via dissociativenized platinum electrode in acid medium, J. Electroanal. Chem.,adsorption of EG at E2= 0.10 V, and this band appears in1983, 147(1-2): 263-278.the spectra at reaction time t > 5 s. The intensity of this8. Lebedeva, N. P, Kryukova, G. N., Tsybulya, S. V. et al, Effcts ofband is increased progressively with increasing t. In themicrostructure in ethylene glycol oxidation on graphite supportedinitial stage, the CO, band center (Vco, ) is blue-shiftedplatinum electrodes, Eletrochim. Acta, 1998, 44(8-9): 1431-with increasing t, indicating that the Vco， changes with1440.COL coverage, and implying that COL species are distrib-9. Cherstiouk, O. V., Savinova, E. R, Kozhanova, L. A. et al, Elec-uted uniformly on Pt(100) surface. In addition, a bandtrocatalytic oxidation of ethylene glycol on dispersed Pt: Determi-near 2342 cm! appears in the spectraat t> 70 s, which is .nation of the reaction products, React. Kinet. Catal. Lett, 2000,assigned to IR absorption of CO2 species that are formed69(2): 331- -338.via direct oxidation of EG. With the increase of E, the0. Gootzen, J. F. E., Visscher, W., Vanveen, J. A. R., Characterizationdirect oxidation of EG becomes gradually the main routeof ethanol and 1,2-ethanediol adsorbates on platinized platinumof EG oxidation, and leads to the decrease of the rate ofwith Fourier transform infrared spectroscopy and differential elec-EG dissociative adsorption on Pt( 100) surface. When E2 >trochemical mass spectrometry, Langmuir, 1996, 12(21): 5076-0.40 V, all EG molcules reaching electrode surface can5082.be oxidized directly into CO2, and the oxidation of EGoccurs mainly via the reactive intermediates that are the1. Beltowska- Brzezinska, M., Luczak, T, Holze, R, Electrocatalyticspecies containing -COOH determined by in situoxidation of mono- and polyhydric alcohols on gold and platinum,TRFTIRS.J. Appl. Electrochem., 1997, 27: 999- -1011.Acknowledgements This work was supported by the National Natural12. Dailey, A., Shin, J,. Korzeniewski, C., Ethylene glycol electro-Science Foundation of China (Grant Nos.20373059 and 90206039) andchemical oxidation at platinum probed by ion chromatography andthe“973" Program (Grant No. 2002CB211804).infrared spectroscopy, Electrochim. Acta, 1998, 44: 1147- - 1152.References13. Gootzen,J. F E, Wonders, A. H., Cox, A. P. et al., On the adsor-1. Lamy, C. 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Sci, 1997, 55: 271-340.(Received October 29, 2004; accepted March 21, 2005)1998Chinese Science Bulletin Vol. 50 No. 18 September 2005