Comparison of the Spinels Co 3 O 4 and NiCo 2 O 4 as Bifunctional Oxygen Catalysts in Alkaline Media

Abstract

Data from experiments with both rotating disc electrodes (RDEs) and gas diffusion electrodes (GDEs) are used to investigate the properties of the spinels, Co3O4 and NiCo2O4, as bifunctional oxygen electrocatalysts. Emphasis is placed on catalyst compositions and electrode structures free of carbon. Oxygen evolution and reduction occur at surfaces where the transition metals are in different oxidation states but the surface can be repeatedly cycled between these two states without significant change. It is shown that carbon-free, NiCo2O4 catalysed GDEs can be fabricated using structures based on stainless steel cloth or nickel foam. Those based on nickel foam can be cycled extensively and allow both O2 evolution and reduction at current densities up to 100 mA cm -2 .

The impact of operating conditions on component and electrode development for zinc-air flow batteries

“…This is in agreement to reported values of other zinc-air battery systems [14,28,[40][41][42][43]. The charge/discharge potentials are nearly the same for all three electrodes indicating that the PIC method is applicable in full cell operation without any harming effect on the air electrode.…”

“…The recharge capability of the zinc electrode is studied with pulse interrupt currents (PIC) on rotating electrodes in order to achieve dendrite-free zinc deposits [21,22]. Concerning the positive electrode, of the many catalysts reported for zinc-air batteries [14,[23][24][25][26] [27][28][29][30]were chosen and both employed in the investigated air electrodes. They bi-functionally catalyze the discharging reaction, i.e., oxygen reduction reaction-ORR, and the charging reaction, i.e., oxygen evolution reaction-OER.…”

Voltammetric Studies of the Mechanism of the Oxygen Reduction in Alkaline Media at the Spinels Co3O4and NiCo2O4

“…Voltammograms of the Co 3 O 4 and NiCo 2 O 4 catalysts used in this study in nitrogen purged 1 M KOH have been previously reported. 18 For comparison purposes, coatings were prepared either with Pt black (Fuel Cell Grade) from E-TEK or XC-72R carbon powder replacing the spinel catalyst, but otherwise prepared by the same procedure. In all cases, the catalyst loading was ∼ 75 μg cm −2 .…”

“…[9][10][11] It is also not a viable component of bifunctional oxygen electrodes because of possible corrosion in the conditions of oxygen evolution. Three recent papers from our group [16][17][18] report oxygen reduction at GDE based on NiCo 2 O 4 catalyst without graphitic carbon. A number of papers have also reported the behavior of nanostructured Co 3 O 4 and NiCo 2 O 4 for oxygen reduction 12,13,[19][20][21][22][23][24][25][26][27][28][29][30][31][32] but the assessment of these data is often hampered by the absence of data at 'standard' surfaces, such as Pt, graphitic carbon, or the uncoated glassy carbon surface, for comparison.…”

Preparation and Electrochemical Properties of NiCo2O4 Nanospinels Supported on Graphene Derivatives as Earth‐Abundant Oxygen Bifunctional Catalysts

“…This is known to improve the electrochemical activity of cobaltites in both the ORR and the OER . Numerous other reports stated that NiCo 2 O 4 is a better catalyst than Co 3 O 4 for the OER . All these reports tend to indicate that NiCo 2 O 4 is the most suitable bifunctional catalyst.…”