Cobalt electrodeposition onto highly oriented pyrolytic graphite (HOPG) electrode from ammonium sulfate solutions

Abstract

It was carried out an electrochemical study of the cobalt electrodeposition onto HOPG electrode from an aqueous solution containing 10 -2 M of CoSO 4 + 1M (NH 4 ) 2 SO 4 . Nucleation parameters such as nucleation rate, density of active nucleation sites, saturation nucleus and the rate constant of the proton reduction reaction (k PR ) were determined from potentiostatic studies. An increase in k PR values with the decrease in the applied potential suggested a competition between H + and Co 2+ by the active sites on the surface. The ∆G energy calculated for the formation of stable nucleus was 8.21x10-21 J/nuclei. The AFM study indicated the formation of small clusters of 50-400 nm in diameter and 2-120 nm in height.

The Effect of Electrolyte pH on the Ni-Co Mixed Oxides Coatings Produced from Citrate Baths

“…Although noble metals, such as Pt, Au, Ag, Ru and Ir, are generally used as electrodes for OER, they have high cost and low stability in alkaline medium [10][11][12] . Therefore, there is a growing demand to replace these metals by alternative catalysts with low cost and similar performance 15,16,18 . Transition metal oxides, such as Ni, Co, V, Fe, as well as Sn oxides, present electrocatalytic properties, which make them attractive alternatives electrodes for several reactions, including OER 16 .…”

“…The NiCo 2 O 4 is not aggressive to the environment and may have different nanostructures. This mixed oxide presents stability, activity and low cost, being active in the oxygen evolution and reduction reactions, in alkaline medium 18,19 and also in the electro-oxidation of amines and alcohols 16 . Even though the production of films in neutral media is encouraged 1 , generally, Ni-Co mixed oxides are electrodeposited using alkaline solutions and studies using others pH ranges are scarcely reported 1,5,[20][21][22] .…”

Analysis of the substrate effect on the nucleation and growth mode of electrodeposited cobalt on copper and graphite electrodes

“…These models are used as theoretical background for the development of more recent nucleation and growth models [19][20][21] that take into account of particular shape of the nuclei (for hemispherical nuclei, see for example Ref. [20]) or process taking place at the same time like proton reduction [19,20,22]. To correlate global physical values to the microscopic scale data obtained by Atomic Force Microscopy (AFM) or Scanning Electron Microscopy (SEM) imaging is a difficult task as well as finding a relationship between the deposition conditions and the topography images of the deposit.…”

“…To correlate global physical values to the microscopic scale data obtained by Atomic Force Microscopy (AFM) or Scanning Electron Microscopy (SEM) imaging is a difficult task as well as finding a relationship between the deposition conditions and the topography images of the deposit. It has been partially undertaken for copper electrodeposited on silicon substrate from pyrophosphate solutions [23], for cobalt electrodeposition onto Glassy Carbon Electrode (GCE) and HOPG substrates from sulphate sodium solutions [19,22,24] and for zinc electrodeposition on GCE [21]. In our paper, we extract characteristic parameters from the Amstrong or Sharifker models and compare them to the AFM images obtained during the first step of growth.…”

“…Graphite supporting electrodes are available for industrial applications (glassy carbon, graphite, HOPG, y) and are interesting substrate for carbon fibres growth activated by catalysts [33]. Recently, glassy carbon electrodes [3,20,24,[34][35][36][37] or HOPG [19,22,24,34,[38][39]40] surfaces have been used in cobalt electrodeposition studies to investigate the cationic influence on the nucleation process of cobalt nano-sized aggregates [34,39]. Kinetic studies [24] and references therein] show that electrodeposition of cobalt is a diffusion-controlled process with a 3-D nucleation mechanism for both substrates (GCE and HOPG) using sodium sulphate baths.…”