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44568-B5
Electrodeposition of Metal Alloy and Mixed Oxide Films Using a Single-Precursor Tetranuclear Heteropolymetallic Complexes

Bizuneh Workie, Delaware State University

Electrochemical Studies and Material Characterization of the Electrodeposited Films of (µ₄-O)(denc)₄Cu₃CoCl₆^.H₂O [denc = N,N-diethylnicotinamide, core structure Cu₃Co], (µ₄-O)(denc)₄Cu₂Co₂Cl₆ [Cu₂Co₂] and (µ₄-O)(denc)₄CuCo₃Cl₆ [CuCo₃] Heteropolymetallic Complexes

In our first report, cyclic voltammetry (CV) studies have shown that Cu₃Co complex is electrochemically active and at higher cathodic potential the complex forms a deposit on the electrode surface.  In this work, we have extended the CV studies to Cu₂Co₂ and CuCo₃, and the results demonstrate similar electrochemical trends for both complexes.  Analogous electrochemical results were also obtained using hydrodynamic rotating disk electrode (RDE) volatmmetry for Cu₃Co and Cu₂Co₂ complexes.  RDE voltammetry experiment of CuCo₃ was not performed due to a very limited amount of sample obtained from the synthesis.  We also conducted scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDS) studies for an electrodeposited film acquired from Cu₃Co complex.

All the heteropolymetallic complexes were synthesized in methylene chloride by means of transmetallation reaction and the by product of the reaction, Cu(NS)₂, was separated from the complexes by gel permeation chromatography. ^1-2  The reactants used for the transmetallation reactions were synthesized according to references 3, 4, and 5.

All CV and RDE voltammetry studies were carried using PAR Model 263A Potentiostat – Galvanostat (PerkinElmer) with three electrodes system consisting of Pt working, Pt wire counter, and Ag/(0.01 M) silver hexafluorophosphate (AgPF₆)-CH₃CN reference electrodes.  The Pt working electrodes for CV and RDE experiments were 3.0 mm diameter (CH instrument Co.) and 1.1 cm (Pine Instrument Co.) disks, respectively.  The Pt working electrodes were polished with 0.05 mm alumina (Buehler), washed with deionized water, sonicated for about 5 minutes, and dried before use.  All experiments were carried out using 1.0 mM solutions of the complexes with 0.20 M tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte in dimethylsulfoxide (DMSO).  The solutions were bubbled with N₂ prior to the electrochemical measurements and blanketed with N₂ while conducting the experiments.

SEM study was performed using an AMRAY 1810T microscope with tungsten filament running at 20 kV.  The EDS system used was an Oxford Instruments Pentafet detector with a SATW window for analysis down to boron.  The energy range typically examined was 1 to 15 kV with a resolution of 134 eV at 5 keV.

Shown in Figure 1 are the CVs of Cu₂Co₂ and CuCo₃ complexes at different switching potentials.  Similar to Cu₃Co, the voltammograms in Figure 1 exhibit the appearance of multiple anodic and cathodic peaks at higher cathodic switching potential.  Switching at - 0.60 V produces a simple and easily reproducible redox couples.  CV studies at a higher cathodic switching potential as a function of pausing time clearly demonstrated an increase of two anodic peaks with pause time increase, Figure 2.  This indicates that the peaks are stripping peaks of an electrodeposited film from the electrode.  Figure 3 shows the RDE voltammograms of Cu₃Co and Cu₂Co₂ complexes.  Both complexes formed electrodeposited films in the potential region of the second plateau region. One-hour potentiostatic hydrodynamic RDE electrodeposition of both complexes at potential of - 1.80 V and a rotations rate of 1600 rpm produced a continuous and well adhered film.  The SEM micrograph of the resulting deposit of Cu₃Co is shown in Figure 4.  EDS study of the base film in the center and at the edge revealed ~90% Cu and 1% Co along with other trace elements consistent with the electrodeposition solution. Further works will be conducted to control the Cu/Co atomic ratio of the Cu₃Co deposit by the metal stoichiometry of the complex and extend the project to other types of heteropolymetallic complexes.

    <>References

1.  Davies, G.; El-Sayed, M. A.; El-Toukhy, A., Chem. Soc. Rev., 1992, 101.

2.  Caulton, K. G.; Davies, G.; Holt, E. M., Polyhedron, 1990, 9, 2319.

3.  Dieck, H. T., Inorg. Chim. Acta, 1973, 7, 397.

4.  El-Toukhy, A.; El-Essawi, M.; Tawfik, M.; El-Sayed, L.; Iskander, M. F., Trans. Met.

    Chem., 1982, 7, 158.

5.  El-Sayed, L.; El-Toukhy, A.;Iskander, M. F., Trans. Met.  Chem., 1979, 4, 300.

Figure 1.  The effect of switching potential on CV of 1.0 mM of the (a) Cu₂Co₂ and (b) CuCo₃ core complexes in 0.20 M TBAPF₆-DMSO at a scan rate of 0.02 Vs^-1.

Figure 2.  CVs of 1.0 mM of (a) Cu₂Co₂ and (b) CuCo₃ core complexes in 0.20 M TBAPF₆-DMSO at a scan rate of 0.02 Vs^-1.  Increasing peak currents correspond with pause time of 0, 10, 20, 40 and 100 s.

Figure 3.  Hydrodynamic RDE voltammograms of 1.0 mM (a) Cu₃Co  and (b) Cu₂Co₂ core complexes in 0.20 M TBAPF₆-DMSO (a'and b') at a scan rate of 0.05 Vs^-1 and rotation rate of 1600 rpm. 

Figure 4.  SEM micrograph of the deposited film from 1.0 mM of Cu₃Co core complex in 0.20 M TBAPF₆-DMSO at a potential of - 1.80 V and rotation rate of 1600 rpm.

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