运用电化学方法，研制了三种表面合金（ＰｂＳｂＰｔ／ＧＣ，ＳｂＰｔ／ＧＣ，ＰｂＰｔ／ＧＣ）电催化剂，发现在草酸还原生成乙醛酸的电有机合成中这些表面合金电催化剂有较高的活性，其起始还原电位分别比在Ｐｂ阴极上（１．１Ｖ）提前了０．４８～０．７０Ｖ。这三种表面合金电催化剂的活性次序为：ＰｂＳｂＰｔ／ＧＣ＞ＳｂＰｔ／ＧＣ＞ＰｂＰｔ／ＧＣ。红外光谱结果表明，在这些表面合金电极上草酸还原产物主要为乙醛酸。作者联系地址：厦门大学化学系固体表面物理化学国家重点实验室Author's Address: Dept. of Chem., State Key Lab. for Phys. Chem. of the Solid Surf.,Inst. of Phys. Chem., Xiamen Univ., Xiamen 36100

Chen Shengpei

Sun Shigang

Xia Shengqing

夏盛清

孙世刚

陈声培

Xiamen University Institutional Repository

第 4 卷 　第 2 期1998 年 5 月电化学EL ECTROCHEMISTR YVol. 4 　No. 2May 1998Studies of surface alloy as high efficientelect rocatalyst for glyoxylic acid synthesis①Chen Shengpei 　Xia Shengqing 　Sun Shigang 3( Dept . of Chem . , S tate Key L ab. f or Phys . Chem . of the Solid S urf . ,Inst . of Phys . Chem . , Xiamen U niv . , Xiamen 361005)The organic electrosynthesis is of advantage in many aspects , such as high selectivity and nopollution to environment . In recent years , with more social attention focused on the environmentand energy problems , the organic electrosynthesis has become an important part in the industry ofgreen synthesis. The synthesis of glyoxylic acid by means of electro2reduction of oxalic acid hasplayed an important role not only in fine chemical industry , spice synthesis and pharmaceuticalchemistry , but also in the fundamental studies of electocatalysis. Lead , carbon and other materi2als are often used as cathodes for this synthesis. However , the problem of high overvoltage is en2countered with these materials. For example , the reduction of oxalic acid on lead cathode takesplace at potentials below 21. 2 V (SCE) [1 ] , which leads to a large consumption of energy. In addi2tion , the generation of by2products (mainly glycolic acid[2 ]) and the corrosion of lead cathode un2der conditions of high current density[3 ] cause also many difficulties in purifying the products. Asa consequence , to develop new electrocatalysts of high selectivity and activity become a key step inadvancing the industrial process of electrosynthesis of glyoxylic acid. In the present paper , threekinds of electrode of surface alloy ( Pb2Pt/ GC , Sb2Pt/ GC and Pb2Sb2Pt/ GC) were prepared andtested for the reduction of oxalic acid , which has thrown a new light into design and preparationof electrocatalyst of high performance for glyoxylic acid synthesis.1 　ExperimentalTwo types of electrochemical cell , an H2type cell and an undivided cell , were used in experi2ments. The compartments of H2type cell are separated by a glass f rit . A satured calomel electrode( SCE) and a platinum foil were used in both cells as reference and auxiliary electrode , respective2① Received 5 Feb , 1998 ; Supported by National Natural Science Foundation3 　To whom correspondence should be addressed© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved.    http://www.cnki.netly. To eliminate the interference of K+ and Cl - f rom SCE reference electrode , the electrochemicalcell was separated from the compartment of reference electrode by a solution bridge. The elec2t rodes of surface alloy were prepared through the following steps : 1) polishing glassy carbon( GC : ª= 8. 0 mm) at first with 4～6 # Jing Xiang sand paper and then with Al2O3 polishingpowder of size 1～0. 3μ. The surface of GC was cleaned afterwards through an ult rasonic bath ;2) depositing galvanostatically platinum layer of different thickness by controlling the chargepassed ; 3) t ransferring this platinized glassy carbon into the solution containing different metalions ( Pb2 + ,Sb3 + ,or both) , and by setting windows of potential cycling to get surface alloy of dif2ferent composition and structure. All solutions were prepared from A. R reagents and Milliporewater supplied from a Milli2Q Lab system. The data were acquired and processed by a micro2com2puter interfaced with a XHD2II potentiostat . The potentials reported in this paper were referredto SCE scale and the potential sweep rate was at 50 mV·s - 1 for all experiments. The experimentswere carried out at room temperature.Fig. 1 　Cyclic voltammogram curve of Pt/ GCa. 10 - 3 mol·L - 1 Pb2 + + 0. 1 mol·L - 1 HClO4b. 10 - 3 mol·L - 1 Sb3 + + 0. 1 mol·L - 1 HClO4c. 10 - 3 mol·L - 1 Pb2 + + 10 - 3 mol·L - 1 Sb3 + + 0. 1 mol·L - 1 HClO42 　Results and discussion2. 1 　Preparation and characterization of surface alloy electrodesThe voltammograms of deposition of Pb2 + or Sb3 +ions on a platinized glassy carbon ( Pt/ GC) are shown inFig. 1. From Fig. 1a a reduction peak is observed at 20. 2V and an oxidation peak appears at around 20. 45 V ,which may be att ributed respectively to the reduction ofPb2 + and the oxidation of deposited Pb. We observe alsoa pair of redox peaks near 20. 08 V and 0. 22 V from thisvoltammogram. In order to ascertain the origin of thispair of peaks , the electrode of Pt/ GC after deposition ofPb , i. e , the surface alloy electrode of Pb2Pt/ GC wasrinsed with Millipore water and transferred to a pure 0. 1mol·L - 1 HClO4 solution. In the voltammogram recordedthe peaks near 20. 52 and 20. 45 V disappeared , and theredox pair of peaks at 20. 08 and 0. 22 V remained. Incomparison with a cyclic voltammogram of Pt/ GC elec2t rode in 0. 1mol·L - 1 HClO4 no peaks appeared at 20. 08and 0. 22 V , it is evident that the pair of peaks at 20. 08and 0. 22 V is due to the reduction and oxidation of sur2face alloy of Pb2Pt . In the case of Sb3 + ( Fig. 1b) the de2·131·第 2 期 　 　　　　　陈声培等 :用于乙醛酸电合成的高效表面合金电催化剂研究© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved.    http://www.cnki.netposition and dissolution current peak are located around 20. 25 and 20. 05 V. When the solutioncontains both Pb2 + and Sb3 + ions , the voltammogram ( Fig. 1c) displayed clearly two pairs of cur2rent peak. One located near 20. 18 and 20. 06 V , due to the reduction of Sb3 + and the oxidation ofSb , and the other at around 20. 52 and 20. 45 V corresponds to the reduction of Pb2 + and the oxi2dation of Pb. It may be noted that f rom all voltammograms in Fig. 1 that the charge integrated inthe negative going potential sweep (N GPS) is always larger than the charge calculated in the posi2tive going potential sweep ( PGPS) , implying that in each potential cycling , a small quantity ofmetal ( Pb ,Sb) was deposited onto the surface of Pt/ GC electrode. So , by controlling the numberof potential cycling we may control the quantity of Pb and Sb deposited on Pt/ GC surface. Theelectrodes of different surface alloy ( Pb2Pt/ GC ,Sb2Pt/ GC and Pb2Sb2Pt/ GC) prepared in this ex2periment were rinsed by pure water and transferred to another cell for further study.2. 2 　Electrocatalytic effects of different surface alloy electrodes for synthesis ofglyoxylic acid via the reduction of oxalic acidFig. 2 　Cyclic voltammogram curve of surfacealloyele2ctrode in 0. 1 mol ·L - 1HClO4 + 0. 2 mol·L- 1 C2 H2O4a. Pb/ Pt/ GCb. Sb/ Pt/ GCc. Pb/ Sb/ Pt/ GCThe voltammograms recorded with three kinds ofsurface alloy electrode prepared in 2. 1 in a solution con2taining 0. 2mol·L - 1 C2 H2O4 are displayed in Fig. 2. Wemeasured that , at potential of 20. 5 V , the reductioncurrent of oxalic acid on Pb2Pt/ GC , Sb2Pt/ GC and Pb2Sb2Pt/ GC is respectively at 20. 5 , 22. 5 and 23. 6 mA·cm2 ,which are much larger than the current of hydrogenevolution in pure HClO4 solution on the same electrode.From these voltammograms we can measure also the on2set potential of reduction of oxalic acid , which is respec2tively at 20. 52、20. 45 and 20. 4 V for Pb2Pt/ GC , Sb2Pt/GC and Pb2Sb2Pt/ GC electrodes. To compare the valueof 21. 1 V for the reduction of oxalic acid on a Pb cath2ode[1 ] , the electrocatalytic effect of these three kinds ofsurface alloy electrode is evident . The reduced productscan be oxided at potentials above 0. 0 V and yielded apeak at about 0. 25 V as shown in the figure. For thesame lower limit of potential sweep , the intensity of cur2rent of the anodic peak due to the oxidation of reduced oxalic acid on Pb2Pt/ GC , Sb2Pt/ GC andPb2Sb2Pt/ GC electrodes is 0. 4、0. 6 and 1. 0 mA·cm22 , respectively. These results demonstratethat the Pb2Sb2Pt/ GC electrode is the most active one among the three electrodes prepared , since·231· 电 　化 　学 　　　　　　　　　　　　　1998 年© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved.    http://www.cnki.netit gives the highest onset potential for C2 H2O4 reduction and the largest current density for the ox2idation of the reduced products. The electrocatalytic activicty of these three types of surface alloyelectrode may be thus arranged in an order of Pb2Sb2Pt/ GC > Sb2Pt/ GC > Pb2Pt/ GC.2. 3 　The identif ication of reduced products of oxalic acid by infrared spectroscopyFig. 3 　Infrared speetra of electrolytic solu2tion of oxalic acid.a. 0. 6 mol·L - 1 C2 H2O4 + 0. 1mol·L21 HClO4b. Solution affer 12 hrs of electroly2sis on Pb2Sb2Pt/ Gc electrodec. 0. 1 mol·L - 1 C2 H2O3 + mol·L - 1 HClO4The IR spectrum of electrolytic solution after 12hours reduction of oxalic acid on a Pb2Sb2Pt/ GC elec2t rode ( Fig. 3b) displayed mainly four peaks of absorp2tion :1 700 cm - 1 、1 315 cm - 1 、1 233 cm - 1 and 1 108cm - 1 . In comparison with the spectra of oxalic acid( Fig. 3a) and that of glyoxylic acid ( Fig. 3c) , these fourpeaks can be assigned as follows :νc = o of C2 H2O4 orC2 H2O3 (1 700 cm- 1) ; νc2c of C2 H2O3 (1 315 cm- 1 ) ;νc2c of C2 H2O4 (1 233 cm- 1) ; the absorption of HClO4(1 108 cm - 1) . These results proved that the electrolyticsolution of reduction of oxalic acid may contain a mixtureof oxalic acid ( C2 H2O4) and glyoxylic acid ( C2 H2O3 ) ,and illust rated that the main product specie of C2 H2O4reduction on Pb2Sb2Pt/ GC electrode is glyoxylic acid.3 　ConclusionsIn the present studies , we have prepared threetypes of surface alloy electrode , and demonstrated thatthese electrodes possess a high activity towards the elec2t rosythesis of glyoxylic acid via the reduction of oxalic acid. The order of activity of these surfacealloy ecectrode has been arranged as Pb2Sb2Pt/ GC > Sb2Pt/ GC > Pb2Pt/ GC. Further work willbe emphasized on studies of the structure of these surface alloy electrocatalysts and on the mecha2nism of the reduction of oxalic acid.Keywords 　Glassy carbon , Surface alloy electrode , Oxalic acid , Glyoxylic acidreference s1 　桂伟志 . 电化学合成乙醛酸. 化学世界 ,1989 ,249 :2 　K. scott , A. P. Colbourne and S. D. Peer. A study of glyoxylic acid synthesis in an undivided cell. ElectrochimicaActa. , 1990 ,35(3) :3 　Keith Scott . A preliminary investigation of the simultaneous anodic and cathodic production of glyoxylic acid ,Electrochimica Acta , 1991 ,36(9) :·331·第 2 期 　 　　　　　陈声培等 :用于乙醛酸电合成的高效表面合金电催化剂研究© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved.    http://www.cnki.net用于乙醛酸电合成的高效表面合金电催化剂研究陈声培　夏盛清　孙世刚 3(厦门大学化学系 ,固体表面物理化学国家重点实验室 ,物化所 ,厦门 361005)摘要 　运用电化学方法 ,研制了三种表面合金 ( Pb2Sb2Pt/ GC , Sb2Pt/ GC , Pb2Pt/ GC) 电催化剂 ,发现在草酸还原生成乙醛酸的电有机合成中这些表面合金电催化剂有较高的活性 ,其起始还原电位分别比在 Pb阴极上 (21. 1 V)提前了 0. 48～0. 70 V。这三种表面合金电催化剂的活性次序为 : Pb2Sb2Pt/ GC > Sb2Pt/ GC> Pb2Pt/ GC。红外光谱结果表明 ,在这些表面合金电极上草酸还原产物主要为乙醛酸。关键词 　玻碳 ,表面合金电极 ,草酸 ,乙醛酸·431· 电 　化 　学 　　　　　　　　　　　　　1998 年© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved.    http://www.cnki.net

Studies of surface alloy as high efficient electrocatalyst for glyoxylic acid synthesis

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Studies of surface alloy as high efficient electrocatalyst for glyoxylic acid synthesis

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