Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn Alloy

Availableonlineatwww.sciencedirect.comCIENCEODIRECTJOURNAL OHRE EARTHSJOURNAL OF RARE EARTHS 24(2006)232-237Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn AlloyLin guanfa(林冠发)2, Zhou genshu(周根树)2, Li Dangguo(李党国)2, Zheng maosheng(郑茂盛)2(1.RInstitute of Goods Tubular, China National Petroleum Cor poration. Xi'an 710065, China;2. School of Material Science and Engineering, Xian Jiaotong University, Xi'an 710049, China)Received 10 October 2005: revised 10 December 2005Abstract: The effect of Ce on the behavior of gas evolution on Pb-Ca-Sn alloy in 4. 5 mol L-1 H2 SO was investigatedusing cyclic voltammetry(CV), cathodic polarization curves and AC impedance(EIS). Cyclic voltammetry experimentsshow that the current of oxygen evolution on Pb-Ca- Sn-Ce electrode is lower than that of Pb-Ca-Sn electrode in the sameanodic voltage. Moreover, the oxygen evolution potential on the former electrode is greater than that on the latter, andthis means that Ce can increase the potential of oxygen evolution on Pb-Ca-Sn alloy. The AC impedance experimentshow that Ce can also enhance the resistance of hydrogen evolution on Pb-Ca-Sn electrode, i.e., Ce can inhibit the hydrogen evolution on Pb-Ca-Sn electrode. The reason why Ce decreases the volume of hydrogen evolution on Pb-Ca-Sn alloy is that Ce increases the resistance of absorbing step of hydrogen evolution reaction. All the experimental results indicate that Pb-Ca- Sn-Ce alloy can rapidly decrease the oxygen and hydrogen evolution on Pb-Ca-Sn-Ce alloy. It is concluded that Pb-Ca- Sn-Ce alloy can promote the maintenance-free property of lead acid battery, and can serve as the canddate of the grid material for maintenance-free lead acid batter,Key words cyclic voltammetry; AC impedance; Pb-Ca-Sn-Ce alloy; rare earthsCLC number: TM9121 Document code: A Article ID: 1002-0721(2006)02-0232-06Hydrogen and oxygen evolution reactions arematerials are Pb-Ca-Sn alloys. The over-potential ofharmful to the valve regulate lead acid battery during hydrogen evolution on Pb-Ca-Sn alloy is higher thanaging and discharging processes. Oxygen evolu- that on Pb-Sb alloy, and with the decrease in thetion reaction occurs at the positive electrode in the volume of gas evolution and water loss for Pb-Ca-Snlead acid battery and transfers from baffle to the alloy, it improves the maintenance-free property ofnegative electrode, reducing to water finally. Hy- the lead acid battery 1-3. However, investigationsdrogen evolution reaction takes place occasionally on find that a high-impedance passive layer at the grid/the negative electrode in the lead acid battery. In active material interface forms in Pb-Ca-Sn alloysgeneral, the rate of hydrogen oxidation reaction on and this layer composing of PbO makes the premathe negative electrode is lower or less hydrogen is ture capacity of batteries decrease rapidly. The maoxidized at the negative electrode, and the hydrogen intenance-free behavior of Pb-Ca-Sn alloescapes from the battery, becoming permanent waIn order to find a grid alloter. Excess gas evolution may lead to the loss of batmaintenance-free property, many novel grid alloys htery capacity prematurely. For maintenance-leTHEn MHGnmaintenance-free lead acid battery, the main gridFoundation item: Project supported by Innovation Fund for Small Technology Based Firms of Natd Technology Administration(03C26216111166)Biography: Lin Guanfa (1960-), Male, Doctoral candidate: Research direction: material sciencecop存葱据。, by editorial Committee of Journal of the Chinese Rare earths Societ. Published by Elsevier B.V. All rights reservedLin g F et al. Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn Alloy233sign and research is how to decrease the volume oftrode (SCe) acted as the counter and reference elec-gas evolution. Alloys with more positive over-potentrodtively. All data for electtial of hydrogen evolution may be the promise soluare reported with respect to this reference electrodetion. Since Ce has a similar electrode potential as the in this paper All the experiments were performed atcalcium element and the over- potential of hydrogen room temperature (25 C)evolution on Ce is also higher, addition ofCyclic voltammetry and linear sweep voltagePb-Ca-Sn alloy may preventgas evolution prowere performed using CHI Instrumentfoundly. Although many investigations have found Electrochemical Working Station. The AC impedthat Ce can significantly promote the deep-cycle ance apparatus consisted of a Solartron Schlumbergproperty of the Pb-Ca-Sn alloys 7-ll, there is no re- er 1250 frequency response analyzer and a Solartronport on the effect of Ce on the gas evolution property 1286 electrochemical interface, the potential was inin Pb-Ca-Sn alloys. In fact, the gas evolution reac- creased by 10 mV and the sweeping frequency wastion during battery charging process is not inhibited from 100 k Hz to 100 mHz. Prior to beginning ex-thoroughly, and the gas evolution is unavoidableperiment, the working electrode was polished with aThe critical problem is the need to decrease the vol- silicon carbide paper of 1200 grit, and washed withof gas evolution. The stability of low calciumdouble-distilled water and dried, and then polarizedand high tin lead alloy is better than that of high calat-1.6V for 20 min to remove the oxidation on thecium and low tin lead alloy Which is the common working electrode surface. The scanning potential ofPb-Ca-Sn alloy in merchandise), and the inter-grain cyclic voltage was in the range of 1.0 to 2.1 V withcorrosion easily occurs on the latter. In order toa scanning rate of 2 mv.s and 100 scanning cyunderstand the effect of Ce on the gas evolutiocles. The linear sweeping voltage was polarized at 1property of Pb-Ca-Sn alloys better, Ce is added into 28 V for 2 h to form the anodic film, and then sweptPb-Ca-Sn alloy and the effect of Ce on the gas evoluto-1.2 V with a scanning rate of 2 mV.stion property of Pb-Ca-Sn alloy in sulfuric acid solution was studied with the cyclic voltammetry mea2 Results and discussionurement,cathodic polarization method and AC im2.1 Characteristics of oxygen evolutionFig 1 shows the cyclic voltammetry of Pb-Ca1 ExperimentalSn and Pb-Ca-Sn-Ce electrodes performed between1.0 and 2.1 v with a scanning rate of 2 mV.sThe electrode alloys were prepared by meltingweighed mixtures of commercial lead (99. 99after 100 cycles in 4. 5 mol. L. H SO. It can be seenmass fraction), commercial tin(99. 99 %, mass fracthat three anodic peaks(1),(2)and(3)appear in thetion), commercial calcium (99. 99%, mass fraction)positive sweeping, and( 4) peak is observed in theind commercial Ce(99.99%, mass fraction)incrucible. and then cast witha iorm or rod(Φ20mmX 200 mm) in copper mould. The rod samples weremanufactured in a form of wafer(Φl0mm×5mm)one of the end surface exposed in the electrolyte ac-ngper of successively decreasing grain size down to athe lo um and others were sealed with epoxy resinin the lower part of an L-shaped glass tube. Table 1 liststhe chemical composition of the electrode alloys.All the electrochemical experiments were performed in a conventional three-electrode cell. and a8202.2piece of platinum mesh and saturated calomel e lecTable 1 Chemical composition (% mass fraction )of e-中国煤化工Sn and pb-Ca-Sn-Ce elec-lectrode alloysCNMHGPb-Ca-Sn-Ce;2-PbIrodesCaSn/ca(1) Peak of Pb( I)compound oxidation; (2) Peak of Pb(lv)0.0451.350.050.013 Balanced30compound oxidation; (3) Peak of oxygen evolution; (4) Peakof Pb( II)compound reduction234JOURNAL OF RARE EARTHS, Vol 24, No 2, Apr. 2006negative sweeping. The peaks(1).(2)and(4)cor- negative potential. This indicates that hydrogen evorespond to the inter-transformation of the lead comlution reaction takes place on Pb-Ca-Sn electrodepounds, peak (3) corresponds to the oxygen evolumore easily than on Pb-Ca-Sn electrode. We can obtion reaction 2 From Fig. 2. it can be found that tain the slops coefficient of the elog plot of thethe current of peak(3)on Pb-Ca-Sn-Ce electrode is two electrodes, 0. 136 and 0. 177 V for Pb-Ca-Sn elower than that on pb-Ca-Sn electrode, moreover thepectively.oxygen evolution potential on Pb-Ca-Sn-Ce electrode This also indicates that Ce can promote the slop co-is greater than that on Pb-Ca-Sn electrode. This imefficient value of Tafel plot for Pb-Ca-Sn alloy.plies that Ce can inhibit the oxygen evolution at the Higher slop coefficient value of Tafel plot corre-potential of peak (3)on Pb-Ca-Sn electrode, and sponds to lower volume of hydrogen evolution, andthen decrease the water loss during charging hence, the volume of hydrogen evolution on Pb-CaSn-Ce electrode is lower than that on Pb-Ca-Sn elecThe oxygen evolution reaction may occur at thepotential of peak (3)on lead electrode as follows:The rare earth element Ce is an extraordinaryH2O→O4+2H++2(1)active metal. which can easily react with the harmfulOa+Oa4→Oelement like oxygen, sulphur, etc, in steel produc-Od+ lead-lead oxidation(3)tion, and then purify the microstructure of the alObviously, the factors which benefit reaction loys. As Ce is added into Pb-Ca-Sn alloys, some(2)do not benefit to the reaction(3), and Ce addedharmful elements can react with Ce easily, andinto Pb-Ca-Sn alloys may improve the absorbing conthereby purifying the microstructure 3. Secondlycentration of oxygen (Od) which reacts with the Ce can make the grain of the alloys fine, as there issubstrate lead to form the lead oxidations. It implieshin film between grains for the fine microstructurethat the addition of Ce is favorable to reaction (3)the corrosion products can cover the grains and theand Ce may prohibit the occurrence of reaction (2)thin film between grains separating the electrolyteand the rate of the oxygen evolution sharply decreaand the substrate, and prevent corrosion. Thirdlyses, then the oxygen evolution on Pb-Ca-Sn-Ce elecCe has similar electrode potential with calcium, liketrode is inhibitedcalcium element, the over-potential of hydrogen evo-2.2 Properties of hydrogen evolutionlution on cerium is high, and it handicaps the hydro-The cathodic polarization curves of Pb-Ca-Sn-Ce gen evolution on cerium. In conclusion, Ce can inand Pb-Ca-Sn electrodes are shown in Fig. 2, andhibit the hydrogen evolution on Pb-Ca-Sn-Ce eleFig 2(a) is the e-j plot, Fig. 2(b) is the e-letrode,and this is helpful to prevent the water lossplot. It is observed that the current densities onand self-discharge occurrence in lead acid batteryboth electrodes increith the potential becoming 2.3 Result of Ac impedancemore negative, the current of hydrogen evolution onTafel plot is often used to describe the rate ofPb-Ca-Sn electrode is larger than that on Pb-Ca-Snthe electrochemical reaction at the cathodic potenCe electrode at the same potential, and the diffetiall4, which can be shown as followsent density between two electrodes ben=a+blog, b2.3RT(4)comes more and more significant with increasing(b)l.181.22TYHa中国煤化工CNMHG ()(2,0.01000150.0200.0250.030Fig 2 Cathodic polarization curves of 1 electrode(1)and 2 electrode(2)(a)e-j plot:(b) E-log plotLin g F et al. Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn Alloy235belectrochemical absorbing reaction, Cp representswhere a and b are constants. Assuming dithe capacity of the absorbed intermediate and QRp, Eg.(4)can be written asthe constant phase element (CPe). The impedance(5) (2) of a CPE can be obtained through the followingSubstituting the eg. (5) into eg. (4), Eg.(6) is obY0(j)0