The Electrochemistry of Metallic Nickel: Oxides, Hydroxides, Hydrides and Alkaline Hydrogen Evolution

Abstract

Ni-based catalysts in aqueous alkaline media are low-cost electrode materials for electrolytic hydrogen generation, a renewable method of producing fuel and industrial feedstock.However, Ni cathodes show a significant decrease in their hydrogen evolution reaction (HER) activity after several hours of electrolysis. Further, industrial electrolysers are often subjected to transient anodic currents, the effects of which on Ni-based catalysts are not well-known. We consider the source of electrode deactivation and the effects of temporary anodic currents on smooth metallic Ni electrodes in alkaline solutions by cyclic voltammetry (CV), galvanostatic and potentiostatic polarization, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Polished surfaces are covered by a bilayer composed of α-Ni(OH) 2 underlaid by nonstoichiometric NiO x . Below the reversible hydrogen electrode (RHE) potential, the air-formed layer mostly reduces to Ni metal and H atoms incorporate deep into the electrode material. Under industrial conditions, i.e., concentrated NaOH/KOH solutions and large cathodic current densities, α-NiH x and β-NiH x can form at the electrode surface. Above the RHE potential, NiO x , α-Ni(OH) 2 , β-Ni(OH) 2 and β-NiOOH form r eversibly and mostly reduce back to Ni on subsequent cathodic polarization. However, repeated oxidation and reduction will introduce strain on a catalyst material, which may lead to its mechanical failure.Hall, D.S.; Bock, C.; MacDougall, B.R. uOttawa/NRC 3

Nickel hydroxides and related materials: a review of their structures, synthesis and properties

“…Presumably, the additional SERS-active β-Ni(OH) 2 peak at 445 cm −1 is convoluted with the α-Ni(OH) 2 peak at 460 cm −1 in the spectra, which reinforces the benefits of examining the O−H stretching 'fingerprint' region. Our interpretation of these results support recent voltammetric peak assignments of Ni in alkaline media; during a forward potential sweep a surface layer of mostly α-Ni(OH) 2 forms over a non-stoichiometric NiO x underlayer [179]. However, the SERS results suggest that β-Ni(OH) 2 is a surface layer component at lower potentials than previously thought.…”

“…de Souza et al 's conclusions are generally consistent with the present understanding of the voltammetry of nickel in alkaline media [179].…”

“…Kostecki & McLarnon [233] measured SERS during long-term voltammetric cycling between Ni(OH) 2 and NiOOH. During such cycling, it is known that the composition of the reduced state is initially α-Ni(OH) 2 and, after cycling, gradually contains a greater β-Ni(OH) 2 component [179]. The SERS spectra of the initial state contains the same α-Ni(OH) 2 lattice modes present in the results of Desilvestro et al After cycling, the spectra contain additional SERS peaks at 445 and 522 cm −1 .…”

“…Ni/NiO/α-Ni(OH) 2 in fig. 9a-i in [179]) samples. It is presently not possible, however, to quantify the components in a mixed α/β-Ni(OH) 2 sample from XPS results.…”

Nickel Electrodeposition on Silver for the Development of Solid Oxide Fuel Cell Anodes and Catalytic Membranes

“…All voltammograms scanned from OCV to several potential regions of −1.1 to +0.9 V, −1.1 to +0.8 V and −0.9 to +0.5 V vs Ag/AgCl. 36,37 At higher Ni 2+ concentrations, a rapid rise in current density is observed toward 2 and NiO: 53,54 Ni…”