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Mechanism of CoPt electrodeposition from hexachloroplatinate solution
Ibro Tabakovic and Jiaoming Qiu Seagate Technology, Research and Development, Minnesota 55435, USA E-mail: Ibro.M.Tabakovic@seagate.com |
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PtCl6-2 +2e = PtCl4-2 + 2Cl- (E0 = 0.481 V vs. SCE) (1)
PtCl4-2 + 2e = Pt +4Cl- (E0 = 0.513 V vs. SCE) (2)
Cyclic voltammetry at Pt electrode obtained in H2PtCl6 solution (NH4Cl- H3BO3-H2PtCl6) reveals two reduction peaks at 0.256V and 0.375V vs. SCE, respectively. The voltammetric experiments (CV, RDE, multisweep CV) indicate that the electroactive species at the first wave is adsorbed PtX6-2 (X= Cl, OH) species, which is reduced through 2-electron transfer to PtX4-2. The reduction of PtX4-2 to Pt occurs along the second wave. Electrodeposition of Pt at GCE, Rh, and Cu electrodes occurs through 4-electron transfer along a single voltammetric wave. The RDE voltammogram of CoSO4 solution (NH4Cl-H3BO3-CoSO4) shows the first wave corresponding to the reduction of protons (E1/2 ~-450 mV vs. SCE) followed by reduction of Co+2 ions at on-set potential around 950 mV. The reduction of Co+2 ions is shifted for more than 300 mV to the cathodic side in CoPt solution (Fig.1)
Fig.1. RDE voltammograms obtained in various solutions, Pt-disc, 300 rpm, 5 mV/s.
Electrodeposition at the controlled potential (ECP) from CoPt solution demonstrated that cobalt is deposited at potentials positive to that required to deposit elemental cobalt. The co-deposition of CoxPt1-x alloys is attributed to the negative enthalpy of CoxPt1-x alloy formation [J. J. Mallet et al., Electrochem. Solid-State Lett. 8, C15 (2005)].