NiFe Foam for Oxygen-Evolution Reaction under Neutral Conditions, Electrolysis of Baking Soda Solution: Catalytic and Mechanistic Studies

Abstract

NiFe oxide-based electrodes are promising compounds for oxygen-evolution reaction (OER), which is essential in metal–air batteries and water splitting. Indeed, OER is of great significance in the energy storage domain. Herein, NiFe oxide-based electrodes have been applied as effective and durable electrocatalysts in the presence of NaHCO3 (baking soda). Compared to corrosive acidic or alkaline solutions, the electrolysis of the baking soda solution toward producing oxygen and hydrogen is highly promising. Surprisingly, NiFe foam, without any anodization or modification, is an efficient and stable electrode for OER at pH= 8.5 (NaHCO3, 0.75 M). In addition, the experiments show that NiO(OH) and not Ni (bicarbonate) is the true catalyst for OER. The surface of the foam was investigated through several methods, including in situ Raman spectroscopy in the presence of NaH12/13CO3. All of the methods indicate the presence of various NiFe (hydr)oxides with different phases on the NiFe foam’s surface. For the NiFe foam at pH= 8.5 (NaHCO3, 0.75 M), the overpotentials for the onset of OER and the activity at 10 mA/cm2 are recorded at 250 and 460 mV, respectively. The Tafel plot of the electrode prepared at pH = 8.5 shows the linearity of the log(i) vs overpotential with a slope as low as 60 mV per decade. The effects of anodization potentials, electrochemically active surface areas, and a proposed mechanism for OER are also discussed. At least one possible pathway for OER could be the reaction of the electrolyte with high valent Ni ions on the surface of the electrode.

Reaction between Nickel Hydroxide and Cerium(IV) Ammonium Nitrate in Aqueous Solution

“…Similarly, the Ni–O and Ni–Ni bond distances are 2.056 and 3.117 Å, respectively, for β-Ni­(OH) 2 /CAN­(t), and 2.032 and 3.106 Å, respectively for β-Ni­(OH) 2 /CAN. The observed bond distances and the presence of Ni­(III) oxidation states suggest the coexistence of β-Ni­(OH) 2 and γ-NiO­(OH) in these compounds. − An enhancement in Ni–O coordination number (6.2) with a reduction in Ni–Ni coordination number (2.5) is observed in β-Ni­(OH) 2 /CAN compared to β-Ni­(OH) 2 and β-Ni­(OH) 2 /CAN­(t). Indeed, adding one drop of deionized water to solid Ni­(OH) 2 and CAN compounds results in Ni­(OH 2 ) 6 2+ (aq) formation, and the formation of this ion causes an enhancement in Ni–O coordination number with a reduction in Ni–Ni coordination number.…”

“…XRD patterns (a), Raman spectra of the prepared β-Ni­(OH) 2 (top), synthetic γ-NiO­(OH) (below*: the related peaks for γ-NiO­(OH)) (b), CAN (c), and γ-NiO­(OH) (purchased from Sigma-Aldrich; *: the related peaks for γ-NiO­(OH)) (d). FTIR (e) and DRS (f) spectra of β-Ni­(OH) 2 .…”

“…Of particular interest among these compounds are Ni compounds, and especially Ni (hydr)­oxides, which have been found to exhibit promising performance in WOR. − Although Ni (hydr)­oxides under alkaline conditions are poor catalysts for WOR, the presence of Fe results in efficient activity toward WOR. Ni (hydr)­oxides under acidic conditions were rarely investigated because Ni (hydr)­oxides are not stable under acidic conditions. − On the other hand, cerium­(IV)­ammonium nitrate (CAN) as a sacrificial oxidant is extensively used to study water-oxidation catalysts (WOCs) . However, CAN is a complicated oxidant, and some points should be considered when using CAN for WOR.…”

Oxygen-Evolution Reaction Performance of Nickel (Hydr)Oxide in Alkaline Media: Iron and Nickel Impurities

“…An OER study was conducted using metallic Ni as a model electrode, as its properties can be manipulated to gain insight into the impact of electrolyte composition and salt content on the reaction . Ni (hydr)­oxide frequently forms a protective layer on metallic Ni such as Ni foil or Ni foam, a phenomenon that is commonly observed even in the absence of any applied potential or in the presence of air. ,, Using a Ni foil coated with Ni (hydr)­oxide as an electrode provides a straightforward platform with no binder for studying the OER. Furthermore, the electrode’s structure offers a large surface area, promoting high OER activity and effective gas bubble formation.…”

“…Water electrolysis is a well-established technology that enables the production of hydrogen and oxygen from water. − It also plays a crucial role in storing intermittent renewable energy sources like solar and wind power. − However, a significant obstacle in water electrolysis is the slow and energy-intensive oxygen-evolution reaction (OER). − Therefore, the search for efficient, stable, affordable, abundant, and environmentally friendly OER catalysts is of utmost importance. − One class of catalysts that has garnered significant attention in recent years is NiFe (hydr)­oxides, known for their high activity and durability for OER. − Their potential applications in various fields continue to be explored. − …”