Transport processes at nickel hydroxide/gold modified electrodes in the presence of an electroactive solution

R. TUCCERI .

Turku

Congreso; ICSM 2014; 2014

ICSM 2014

Nickel hydroxide is an important electroactive material for many applications in the field of chemical analysis and electrocatalysis [1-3]. Transport properties of nickel hydroxide films electrochemically deposited on gold were studied in the presence of the Fe(CN)63-/4- redox active couple. Rotating Disc Electrode Voltmmetry (RDEV) was employed to analyze the dependence of limiting currents on electrode potential, electrode rotation rate and voltammetric charge value of the nickel hydroxide film. The voltammetric charge of the nickel hydroxide films was varied within the range 1 < Q < 15 mC cm-2. While anodic limiting currents were observed at potential values more positive that E = 0.6 V (vs. SCE), cathodic ones were observed at potential values lower than E = 0.0 V (vs. SCE). Anodic limiting currents follow the Levich`s equation and are independent of the voltammetric charge value of the nickel hydroxide film (Fig. 1). Cathodic limiting currents depend on the voltammetric charge value and respond to a reactant membrane diffusion phenomenon within the film (Fig. 1). While the anodic process was related to a fast charge transfer process at the Ni(OH)2|Fe(CN)63-/4- solution interface, the cathodic one was attributed to the physical diffusion of the electroactive Fe(CN)63- species across the nickel hydroxide film. A diffusion constant value for the Fe(CN)63- transport through the nickel hydroxide film was obtained. Also, a diffusion constant for the electron transport process across the nickel hydroxide film was extracted considering the existence of a mediation reaction at the Ni(OH)2|Fe(CN)63-/4- interface. The last constant was considered to be the electron transfer rate between Ni2+ and Ni3+ active redox centers into the nickel hydroxide film. Diffusion constant values for nickel hydroxide films were compared with diffusion constants obtained for poly(o-aminophenol), an electroactive polymer that also contains redox active centers and is able to act as mediator in the presence of different redox couples in solution.