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 (NaHCO3)-C-12/13. 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/cm(2) 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.