Surface Structure Dependence of Electrochemical Processes at Monocrystalline Nickel Electrodes. Part 2: The Hydrogen Oxidation Reaction

Abstract

Nickel single crystals grown with the innovative Controlled Atmosphere Flame Fusion (CAFF) technique are used to study the hydrogen oxidation reaction (HOR) on high-quality Ni(111), Ni(100), and Ni(110) electrodes. Cyclic voltammetry (CV) profiles are acquired in both N₂-saturated and H₂-saturated 0.10 M aqueous NaOH solution and compared. Linear sweep voltammetry (LSV) measurements conducted at a very low potential scan rate (s = 0.10 mV s^–1), which ensures steady-state conditions, are performed in the anodic and cathodic directions, from which Tafel plots are constructed and the exchange current density (j₀) and Tafel slope (b) are determined. The resulting Tafel plots are unique to each monocrystalline electrode and also depend on the scan direction; thus, the surface arrangement of atoms and the pretreatment of the electrode influence the values of j₀ and b. CV measurements are used to analyze the surface of the Ni(hkl) electrodes after the HOR and to determine if the process brings about any surface-structural changes. An analysis of the CV profiles leads to the conclusion that the long-range atomic order of the Ni(hkl) electrodes becomes disturbed. This study marks the first ever comprehensive investigation of the HOR on Ni(hkl) electrodes, hence its originality and importance.