Eneli Härk

Electroreduction of Hexaamminecobalt(III) Cation on Bi ( h k l ) Electrodes from Weakly Acidified LiClO4 Solutions

The cyclic voltammetry and rotating disk electrode methods have been used for investigation of electroreduction kinetics of the hexaamminecobalt(III) cations on the electrochemically polished Bi planes. The rate constant for the heterogeneous electroreduction reaction of the [Co(NH 3 ) 6 ] 3+ cation on the Bi(001) and Bi(011) planes in x M LiClO 4 + 0.001 M HClO 4 aqueous base electrolyte solutions has been established and the results have been compared with the data for the Ag(110), Au(hkl), and Hg electrodes as well as with the data for Bi(hkl) in x M HClO 4 solutions. In the region of zero charge potential, the value of the experimental transfer coefficient α exp is slightly higher than 0.5 and depends on the crystallographic structure of the Bi plane. For more concentrated base electrolyte solutions, the values of apparent transfer coefficient α app , corrected for the double-layer effect, are practically independent of the base electrolyte concentration and slightly depend on the electrode polarization. Noticeably different values of the double-layer-corrected rate constant k 0 het and α app for the Bi(001), Bi(011), Bi(lll), Hg, and Ag(110) electrodes from the data for Au(hkl) planes have been explained by the different water and ClO - 4 adsorption energies at the metals under discussion.

The electrochemical activity of two binary alloy catalysts toward oxygen reduction reaction in 0.1 M KOH

The platinum group metals (Pt, Ir and Ru) and the carbide-derived carbon support with the very high specific surface area were used to synthesise the low noble metal loading Pt-C, IrPt-C and RuPt-C alloy catalysts. The alloying of the platinum group metals in the studied catalysts was proved by the several independent physical characterization methods like: the X-ray diffraction, time of flight secondary ion mass-spectrometry, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The electrocatalytic activity toward oxygen reduction reaction of the synthesised catalysts in an alkaline solution was studied and compared with the commercially available Pt-Vulcan. The combined and detail approach using the transmission electron microscopy and inductively coupled plasma mass spectrometry for estimation of the surface area of metal particles is provided. The noticeably higher calculated mass corrected and specific kinetic current density values for Pt-C catalyst were established. For IrPt-C and RuPt-C alloy catalysts, mass corrected current density values are comparable with the commercial Pt-Vulcan. The specific kinetic current density values increase in the following sequence: RuPt-C < IrPt-C < Pt-Vulcan < Pt-C.