Methods—On the Reliability of the Electrochemical Data Recorded on Nickel Foam in Alkaline Solution: The Illusive Surface Oxide Layer

Abstract

The extensive application of nickel foam (Ni foam) as current collector in supercapacitors has raised caveats on the contribution of the redox-active Ni foam to the measured capacities. However, due to the overlooked qualitative features (i.e., shapes) of the cyclic voltammograms (CVs), the redox reaction of the Ni foam oxide layer (NiFOL) has been frequently confused with the true electrochemical signature of the coated materials in alkaline solution. Herein, experimental CVs, scanning electron microscopy images, and estimations reveal that due to the high porosity of the Ni foam and its surface reactivity in alkaline solution (1-6 M KOH), the redox peak couple of the NiFOL can potentially be confused with or lead to misinterpretation of the true electrochemical features of the coatings. A classification of previous papers on a group of metal oxides investigated as battery-type or pseudocapacitive electrodes in the positive potential window is also presented to reveal the confusion between NiFOL and the coating when operated in alkaline solution.

Strengthening the Stability of the Reconstructed NiOOH Phase for 5-Hydroxymethylfurfural Oxidation

“…The first oxidation peak is classified as Ni­(0–II) (−0.2–0.15 V vs Ag/AgCl), and the current density of the second oxidation peak (0.35–0.55 V vs Ag/AgCl) is lower than that of the first CV curve, demonstrating that the low-valence species on the surface of Ni­(OH) 2 gradually transform to NiOOH species (Figure S6d). , …”

“…The first oxidation peak is classified as Ni(0− II) (−0.2−0.15 V vs Ag/AgCl), and the current density of the second oxidation peak (0.35−0.55 V vs Ag/AgCl) is lower than that of the first CV curve, demonstrating that the lowvalence species on the surface of Ni(OH) 2 gradually transform to NiOOH species (Figure S6d). 41,43 As can be seen from Figure 3a, the first CV curve of 14%Ce-Ni(OH) 2 contains two oxidation peaks, corresponding to Ni(0−II) (−0.2−0.15 V vs Ag/AgCl) and Ni(II−III) (0.35− 0.6 V vs Ag/AgCl). 44 In the second CV curve, the extra oxidation peak may belong to hydrogen desorption at −0.45 V vs Ag/AgCl (Figure 3b).…”

Effect of Redox Additive in Aqueous Electrolyte for Electrochemical Energy Storage Applications of A and B Site Ordered LaCaCoCrO6 Double Perovskite

“…In comparison to LaCaCoCrO 6 , the specific capacitance of nickel foil used is almost negligible. [ 64 ] Therefore, the influence of Ni foil on electrode performance might be neglected.…”

Highly Durable Compositionally Variant Bifunctional Tetrametallic Ni–Co–Mn–Fe Phosphide Electrocatalysts Synthesized by a Facile Electrodeposition Method for High-Performance Overall Water Splitting

“…However, recently, many studies revealed the electrocatalytic activity of Ni foam toward OER and HER as it develops a passive oxide layer on the surface once immersed in the electrolyte. This oxide layer might lead to interference with the recorded electrochemical activity of the actual catalyst, leading to misleading results . To this end, Ti mesh, as a low cost material ($.23/inch), was proven to be a suitable substrate due to its large-surface area, high stability in different pH values, and high corrosion resistance .…”

“…This oxide layer might lead to interference with the recorded electrochemical activity of the actual catalyst, leading to misleading results. 43 To this end, Ti mesh, as a low cost material ($.23/inch), was proven to be a suitable substrate due to its large-surface area, high stability in different pH values, and high corrosion resistance. 44 More importantly, Ti mesh showed very low activity toward water electrolysis.…”