On the Catalytic Activity and Corrosion Behavior of Polycrystalline Nickel in Alkaline Media in the Presence of Neutral and Reactive Gases

Abstract

Nickel (Ni) is an important catalytic metal that finds application in electrochemical energy technologies, such as alkaline water electrolyzers (AWEs) and alkaline fuel cells (AFCs). An essential property that determines nickel’s applicability in AWE and AFC technologies is its stability under operating conditions, i.e., performance at extreme potential (E) conditions and in the presence of reactive gases. However, the electrochemical and electrocatalytic behavior of nickel is not as well understood as that of noble electrocatalytic metals such as platinum. This lack of knowledge needs to be addressed prior to dedicating significant efforts to the design, fabrication, and characterization of Ni-based materials for electrochemical energy technologies. We report experimental data on the catalytic activity and corrosion behavior of polycrystalline Ni in the presence of different dissolved gases. Cyclic voltammetry (CV) and potentiodynamic polarization (PDP) measurements are conducted at room temperature in 0.10 M aqueous NaOH solution saturated with either N2(diss), H2(diss), or O2(diss). CV measurements are performed using different potential scan rates in the regions of α-Ni(OH)2 and NiOOH formation/reduction. PDP measurements are conducted in the same electrolyte and in the presence of different dissolved gases but over a much broader potential range (−0.40 V ≤ E ≤ 2.20 V) and at a very low potential scan rate (s = 0.10 mV s−1) to achieve steady-state conditions. The influence of the state of the electrode’s surface (metallic versus oxidized) on the catalytic activity and corrosion behavior of nickel is also investigated by applying two different types of conditioning. The results demonstrate that the electrochemical behavior of Ni changes depending on the nature of the dissolved gas. The corrosion behavior is shown to depend on the polarization direction, thus the surface state of the electrode, and the nature of the dissolved gas. A graph, which is an extension of the Pourbaix diagram for Ni, summarizes the main interfacial and faradaic processes occurring at the surface of polycrystalline Ni in relation to the potential. The results and their analysis are expected to benefit renewable electrochemical energy technologies, such as alkaline water electrolyzers and fuel cells. In addition, they will serve as standards in electrochemical and electrocatalytic characterization of monocrystalline Ni materials and Ni-based nanomaterials.