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

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.