(graphite) rod which is immersed in the elec-trolyte in the centre of the cell is the positiveterminal or cathode. Zn-C dry cells are thecheapest primary batteries and this makesthem very popular for use in many types ofdevices and appliances. The aim of this work isto find out if ZnO nanostructures were formedon the Zn electrode of the Zn-C dry cell [1-8].

M AT E R I A L S A N D M E T H O D SZn electrodes from used Zn-C dry cellSamples of Zn electrodes from Zn-C dry cellsthat had been used for a complete life periodwere collected. The surface of the Zn electrodewas not treated with any etchant. The innersurface of the Zn electrode that was in contactwith the electrolyte was examined using aSEM. Figure 1a shows the Zn casing of the Zn-C dry cells. Figures 1b and 1c show the elec-trolyte and the C-electrode in an opened Zn-Cdry cell.

Scanning Electron MicroscopyThe inner surface of the Zn electrodes that wasin contact with the electrolyte was examinedwith a JEOL JSM-6480LV scanning electronmicroscope.

Energy-Dispersive X-ray SpectroscopyEDX analysis was performed on a JEOL JSM-6480LV scanning electron microscope using anOxford INCAPentaFET-X3 energy-dispersive X-ray spectroscopy system with a high-angleultrathin window 30 mm2 Si(Li) X-ray detector

B I O G R A P H YSyed Nasimul Alamreceived his BTech in1997 from the IndianInstitute of Technologyat Kharagpur, India, inmetallurgical and mate-rials engineering and hisMS in photonics and electronic materialsfrom the Chemical and Nuclear EngineeringDepartment at the University of Massachu-setts, Lowell, USA. He is currently an assis-tant professor at the National Institute ofTechnology-Rourkela, India. His area ofinterest is nanomaterials, X-ray diffractionand microscopy.

A B S T R A C TZinc oxide (ZnO) is a unique material thatexhibits semiconducting as well as piezo-electric properties. ZnO has a very rich fam-ily of nanostructures. Here an effort hasbeen made to find out if there is formationof ZnO nanostructures in the Zn electrode ofa Zn-C dry cell. Zinc electrodes from fullyused Zn-C dry cells have been used for theanalysis. Scanning electron microscopy(SEM) and energy dispersive X-ray spec-troscopy (EDX) analysis of the ZnO structuresformed on the Zn electrode of a Zn-C drycell were performed. The results clearlyshow the formation of ZnO nanostructuresin the Zn-electrode of the Zn-C dry cell. EDXanalysis suggests the ZnO nanostructuresare not pure and stoichiometric.

K E Y W O R D Sscanning electron microscopy, energy-dis-persive X-ray spectroscopy, zinc oxide, Zn-Cdry cell, nanostructures

A C K N O W L E D G E M E N T SWe would like to thank Mr R. Patnayak forhelping us in analyzing the samples usingSEM. We would also like to thank the staffof the heat treatment laboratory at NIT-Rourkela.

A U T H O R D E TA I L SSyed Nasimul Alam, Metallurgical and Materials Engineering,National Institute of Technology Rourkela,Rourkela, Orissa Pin-769008, IndiaTel: +91 9937 917811Email: nasimulalam@yahoo.com

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ZNO NA N O S T R U C T U R E S

I N T R O D U C T I O NZinc oxide (ZnO), a representative of II–VI semi-conductor compounds, is a technologicallyimportant material. ZnO has a unique positionamong the semiconducting oxides due to itspiezoelectric and transparent conductingproperties, high electrical conductivity andoptical transmittance in the visible region.These properties make ZnO ideal for applica-tions such as transparent conducting elec-trodes in flat panel displays and window layersin thin film heterojunction solar cells.

Nanostructures have attracted the attentionof researchers for their many important tech-nological applications and ZnO has beenfound to have a very wide range of nanostruc-tures. Zinc is an integral and a very importantpart of the zinc-carbon (Zn-C) dry cell battery.A Zn-C dry cell is packaged in a Zn casing thatserves as both the container and the negativeterminal. The objective of this analysis was tofind out if ZnO nanostructures were formed inthe Zn electrode of the Zn-C dry cell. The posi-tive terminal of the Zn-C dry cell is usually acarbon rod or graphite rod surrounded by theelectrolyte. The electrolyte is a mixture com-posed of manganese (IV) dioxide (MnO2),ammonium chloride (NH4Cl) and zinc chloride(ZnCl2). It is added to starch to make a thickpaste and also to maintain the moisture in theelectrolyte. The MnO2 is mixed with carbonpowder to increase the electrical conductivity.In the Zn-C dry cell the Zn casing, which is thenegative terminal, is the anode and the carbon

Zinc Oxide Nanostructures in the ZincElectrode of a Zinc-Carbon Dry CellSyed Nasimul Alam and Madhukar Poloju Metallurgical and Materials Engineering Department, National Institute of Technology Rourkela, Orissa, India

Figure 1: (a) A used Zn-C dry cell showing the zinc casing that serves as both the container andthe negative terminal. The carbon or graphite rod positive terminal is surrounded by theelectrolyte which is a mixture of MnO2, NH4Cl and ZnCl2.(b, c) Electrolyte (e) and the carbon electrode (c) in an opened Zn-C dry cell.

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e c

a

b c

that was liquid-nitrogen cooled. An accelerat-ing voltage of 25 kV was used with a 1 nmprobe with ~1 nA of current on the specimen.

R E S U LT S A N D D I S C U S S I O NThe Zn-C dry cell consists of a zinc casing whichacts as the negative terminal and a carbon orgraphite rod which acts as the positive termi-nal. The electrolyte is made up of manganese(IV) dioxide (MnO2), ammonium chloride(NH4Cl) and zinc chloride (ZnCl2). When theexternal switch is closed, an atom of Zn on theZn electrode is oxidized to Zn2+ ion, liberatingtwo electrons. The reaction which takes placein the dry Zn-C dry cell is as follows:

Zn(s) → Zn2+ + 2e–

2NH4+(aq) + 2e– → H2(g) + 2NH3(aq) 2MnO2(s) + H2(g) → Mn2O3(s) + H2O(l) Zn2+ + 2NH3(aq) → Zn(NH3)2

2+ (aq)Although there could be several other reac-tions taking place, the overall reaction in a Zn-C dry cell can be represented as:

Zn(s) + 2MnO2(s) + 2NH4+(aq) → Mn2O3(s)+ Zn(NH3)2

2+(aq) + H2O(l)One of the reactions that could lead to the

formation of ZnO in the Zn electrode is:H2O(l) → H+(aq) + (OH)– (aq)Zn(s) + 2OH– (aq) → ZnO + H2O + 2e–

A reaction of this type is likely to result in theformation of ZnO. It has also been reportedearlier by Wu et al. [7] that Zn(OH)4

2– decom-poses and forms a nucleus for the growth ofZnO crystals when the solution was placed intothe 50°C water bath.

Figures 2a and 3 show the SEM image of theZn casing of a completely used 1.5 volt Zn-Cdry cell. Each hierarchical structure of ZnO con-sists of many nanorod arrays as its secondarystructure. From the magnified SEM image wecan see symmetrical rod-arrays. These arrays ofrods comprising the hierarchical structure canbe divided into two categories, namely pri-mary rod arrays (PRAS) and secondary rod

Figure 4: Energy-dispersive X-ray analysis of the ZnO formed in the Zn electrode of a Zn-C dry cell.

Figure 2: (a) Scanning electron microscope image of the surface of the Zn electrode of a Zn-C drycell. Arrows: ZnO structure illustrating clearly the SRAS distribution. (b) Schematic showing the relative position of the SRAS [7].

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Figure 3: Scanning electron microscope image of the surface of the Zn electrode of a Zn-C dry cell.

a b

ZNO NA N O S T R U C T U R E S

MICROSCOPY AND ANALYSIS SEPTEMBER 2010 11

Figure 5: Schematic showing the details of how the PRAS and the SRAS grow and the formation process of the hierarchical structure.

arrays (SRAS) [7]. The PRAS are formed into aline while the SRAS look like branches comingout of the PRAS. SRAS which are located atboth ends of the PRAS form an angle of 60°with each other, while the SRAS located at theinner area of PRAS are parallel to each other.The tips of the ZnO rods in both PRAS andSRAS are pointed. According to previous work,the first formed stem can provide its six pris-matic planes as the platforms for the latergrowth of the branches. The legs of the star-like structures have a thickness of just less than100 nm. The legs of the star-like structurespreferentially grew along the [0001] direction[8-10]. The lengths of the legs are around 0.5µm (refer to Figures 2a and 3).

The EDX analysis of the ZnO structures isshown in Figure 4. Apart from Zn (at. % =48.07 %) and O (at. % = 44.79 %) there is alsothe presence of a small amount of Cl (at. % =7.14 %). As discussed earlier the electrolyte inthe Zn-C dry cell is composed of manganese(IV) dioxide (MnO2), ammonium chloride(NH4Cl) and zinc chloride (ZnCl2). Cl in the ZnOstructures has possibly come from the elec-trolyte. The Cl in the ZnO structures must havecome from the Cl in the ammonium chloride(NH4Cl) and zinc chloride (ZnCl2) in the elec-trolyte. This suggests that the ZnO structuresare not very pure and have trace amounts ofelements such as Cl.

The ZnO prefers to grow along the c-axisand the (0001) plane. The first formed ZnOstem provides its six prismatic planes as theplatforms for the later growth of thebranches. The process of formation of thehierarchical structure starts with the genera-tion of the nanorods. The nanorods after theirformation are aligned together and fused intoa wall to form the PRAS. For the rods locatedon each end of a PRA, two of their six planescannot act as a platform due to the spatial bar-rier (marked as green lines with arrow heads atboth ends in the schematic diagram in Figure2b). In contrast, for the rods located inside aPRA, only two of the six planes can act as theplatform for the later growth of the SRAS(refer to Figure 2b) [7-10].

Initially the formation of ZnO is very slowand gradually the small ZnO particles fuse toform the ZnO nanorods. First the nanorodswere formed along the [0001] direction. Then,the formed rods aggregated side by side toreduce their surface energy and finally fusedto form a wall. However, when the rate of thegrowth of ZnO structures became very rapid,the prismatic planes of the ZnO rods that havealready formed act as the substrates to com-pensate the rapid growth rate. This is the stagewhen the secondary rod arrays are formed [7].The schematic in Figure 5 shows the details ofhow the PRAS and SRAS are formed.

Apart from the hierarchical structure, rod-like structures of ZnO could also be seen. Therod-like structures of ZnO are mostly nanos-tructured. Figures 6 a-e clearly show the for-mation of ZnO nanorods in the Zn electrode offully used Zn-C dry cell. It can be seen from theEDX analysis of the ZnO nanostructures thatthey are not very pure and stoichiomteric. The

Figure 6: (a-e): Scanning electron microscope images of Zn casings of various used Zn-C dry cells showing the formation of ZnO nanorods.

e

d

a b

c

EDX analysis shows presence of other elementssuch as Cl, K and Pb. The at. % of oxygen in thenanostructures is very high. EDX analysis of thenanorods was also done and is reported in Fig-ure 7. In one of the samples the at.% of oxy-gen was 43.45 whereas the at.% of zinc was23.38. This clearly proves that the nanostruc-tures are not of high purity ZnO and also notstoichiometric. Apart from this, elements likeCl (11.59 at.%) were also seen in the ZnO struc-ture.

C O N C L U S I O N SThere is clear indication of the fact that the Zncasing of the Zn-C dry cell gets oxidized due tothe electrochemical reaction with the elec-trolyte of the cell forming ZnO nanostructures.The nanostructures of ZnO are of variousshapes. Rod-like, wire-like and star-like nanos-tructures of ZnO have been found in the sur-face of the Zn electrode of the Zn-C dry cellthat is in contact with the electrolyte. The ZnOnanostructures do not have very high purityand are also not highly stoichiometric.

R E F E R E N C E S1. Subramanyam, T. K., Naidu, B. Srinivasulu, Uthana, S.

Structure and Optical Properties of DC Reactive MagnetronSputtered Zinc Oxide Films. Crystal Research Technology34(8):981–988, 1999.

2. Wang, Z. L. Zinc oxide nanostructures: growth, propertiesand applications. J. Physics Condensed Matter.16:R829–R858, 2004.

3. Yawong,O., Choopun, S., Mangkorntong, P.,Mangkorntong, N., Chiang M. Zinc Oxide Nanostructure byOxidization of Zinc Thin Films. University Journal SpecialIssue on Nanotechnology 4(1), 2005.

4. Stolt, L., Hedstrom, J., Kessler, M., Ruckh, Velthaus, K. O.,Schock, H. W. ZnO/CdS/CuInSe2 Thin Film Solar Cells withImproved Performance. Applied Physics Letters 62:597,1993.

5. Eveready Carbon Zinc (Zn/MnO²), Application ManualEveready Battery Co. Inc., pp. 1-13, 2001.

6. www.scribd.com/doc/24475365/Primary-Cell-Types-Dry-Cell-Alkaline-Cell-Lithium-Cell. Accessed June 2010.

7. Wu D., Bai, Z. and Jiang K. Temperature inducedhierarchical growth of ZnO microcrystal. Materials Letters63:1057–1060, 2009.

8. Huang, M. H., Mao, S., Feick, H., Yan, H. Q, Wu, Y. Y., Kind,H. Room Temperature Ultraviolet Nanowires Nanolasers.Science 292:1897–1899, 2001.

9. Li, W. J., Shi, E. W., Zhong, W. Z., Yin, Z. W. J. Growthmechanism and growth habit of oxide crystals. Cryst.Growth 203:186–196, 1999.

10. Greene,L. E., Law, M., Tan, D. H., Montano, M., Goldberger,J., Somorjai, G. General Route to Vertical ZnO NanowireArrays Using Textured ZnO Seeds. Nano Letters5:1231–1236, 2005.

©2010 John Wiley & Sons, Ltd

Figure 9: Energy-dispersive X-ray analysis of the ZnO hierarchical structure formed in the Zn electrode of a Zn-C dry cell.

Figure 8: Scanning electron microscope image of Zn casing of a used Zn-C dry cell showing the formation of a ZnO hierarchical structure that has notgrown completely.

Figure 7: Energy-dispersive X-ray analysis of the ZnO nanorods formed in the Zn electrode of a Zn-C dry cell.

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