Shaari, Abdul Halim

Silong, Sidik

Tan, Wee Tee

Universiti Putra Malaysia Institutional Repository

UPM Research Report 1998: Volume 2=.ELECTROCHEMICAL STUDIES OF SOME ORGANICCONDUCTING! SUPERCONDUCTING MATERIALS(SYNMET ALS)Tan Wee Tee, Sidik Silong and Abdul Halim ShaariFaculty of Science and Environmental StudiesUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: organic materials, solid state voltammetry,reaction mechanism.IntroductionThe abrasive stripping voltammetry (AbrSV) or solid statevoltammetry described recently by Scholtz and Lange(1992), Bond et a1. (1994. 1997) was used to extract electro-chemical properties of compounds such as some organome-tallic compounds in water which would otherwise prove im-possible as these compounds are insoluble in water. In re-cent years, the discovery of a number of organic. chargetransfer (CT) salts, known as synthetic metals (synmetals)including TCNQ-TIF (TCNQ = 7,7,8,8 tetracyano-p-quinodimethane and TTF= Tetrathiafulvalene) and more re-cently the discovery of fullerenes (Coo) and its salt: fulleride(e.g. K3Coo) have been found to exhibit superconductingproperties (Williams et al. 1992). Some could exhibit thisproperty even near ambient temperature and pressure. Al-though electrochemical information of these compoundshave been determined however these information are mainlyconfine to solution(voltammetry) rather than solid state volt-ammetry.Materials and MethodsCyclic voltammetry (CV) and square wave voltammetrywere employed to study the electrochemical oxida-tion/reduction of nanocrystals of TTF, TCNQ,Cooand TTF-TCNQ synmetal attached mechanically at the surface of theglassy carbon electrode (3 mm diameter) and immersed in anaqueous electrolyte solution separately. Various parametersincluding pH, type of electrolyte and its concentration werevaried to study the effect on the voltammogram. Redox(multiple) cycling (CV) was also carried out to examine thereproducibility and stability of the redox materials generatedat the electrode surface. Effects of varying scan rate and scanreversal in cyclic voltammetry and the current time wave-form behaviour in chronoamperometry were also assessed inorder to determine the mechanism of the electrode reactionoccurring at the electrode-solid-electrolyte interfaces. Mor-phological changes and insertion of ion(s) occurring at theelectrode surfaces during cyclic voltammetry were examinedby in-situ electrochemical optic~l mi~roscopYf scanningelectron microscopy and energy dispersive x-ray spectrom-metry.Results and DiscussionThe overall electrochemical processes of TTF and TCNQ oc-curring at the electrode-solid-electrolyte interphases mostlikely follow the general equation:300xTTF + yX-X=Br,Cl, I, CIO.(solid) (aq.) (solid)xTCNQ + ye' + yM' = (M+)y(TCNQ")y(TCNQ)x_yM=K,Na,Li,NR4(solid) (aq.) (solid)x Coo+ ye' + y(nNBU4+) = (nNBu/),(C60 -)y(Coo )x'Y(solid) (nonaq.) (solid)It was found that by a combination of the above mentionedvoltammetric techniques that the overall process is under therate control by nucleation and growth of the solid phases. Inthe redox cycling of nanocrystals of TTF, TCNQ and C60 un-usual inert zone or hysteresis was observed between the oxi-dation and re-reduction peaks for TTF unlike those seen inthe conventional redox cycling of solution species in non-aqueous electrolyte. The presence of hysteresis, the observa-tion of maxima, a characteristic feature of cross over of scanreversal into the anodic and cathodic curves in cyclic volt-ammetry and the non-monotonic rising current transient ob-served during chronoamperometry, are evidences of nuclea-tion and growth processes. TTF-TCNQ (1:1) synmetal wassynthesised and characterised electrochemically. Differencesbetween its solution voltammetry and solid state voltamme-try using CV mode were observed and were similar to thoseof the starting materials.ConclusionsThe electrode reactions of TTF. TCNQ, TTF-TCNQ syn-metal and Coooccurring at the electrode-solid-electrolyte in-terfaces can be characterised by the nucleation and growthprocesses.ReferencesBond. A.M. and Marken. F. 1994.Machanistic aspects of the elec-tron and ion transport processes across the electrode(solid),solvent(electrolyte)interface of microcrystalline deca-methylferrocene attached mechanically to a graphite electrode.Llilectroanal. Chern. 372: 125-135.Bond, A.M., Colton, R., Snook, G.A.. Mahon. P.l. and Tan, W.T.1997. Tetrabutylammonium cation expulsion versus perchlorateelectrolyte anion uptake in the electrochemical oxidation of mi-crocrystals of «CJI9}.N)(Cr(CO);1) mechanically attached to agold electrode : a voltammetric and quartz crystal microbalancestudy.l. Solid State Electrochem: 1: 53-61.Sholtz, F. and Lange, B. 1992. Abrasive Stripping Voltammetry-Anclectroanalytical solid state spectroscopy of wide applicability.Trends in Analytical Chemistry. 11(10): 359-367.Wiliams, I.M., Ferraro, I.R., Thorn, RJ .• Carlson, KD., Wang.RH., Kini, A.M., and Whangbo, M.H. 1992. "Organic supercon-ductors". Prentice Hall, NI.Supported by [RPA Grant 09"()2-04·005J

Electrochemical studies of some organic  conducting/superconducting materials (synmetals)

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Electrochemical studies of some organic conducting/superconducting materials (synmetals)

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