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

Abstract

The mechanism of O 2 reduction at the spinels, Co 3 O 4 and NiCo 2 O 4 , in KOH electrolyte is probed using voltammetry at rotating disc and rotating ring-disc electrodes by examination of the rotation rate dependent limiting currents. The analysis shows that the products and mechanisms at the two spinels are quite different. At the cobalt spinel, a substantial amount of the 2e − reduction product, H 2 O 2 , is formed while at NiCo 2 O 4 the 4e − reduction strongly predominates. In terms of both the overpotential for reduction and its limiting current density, the mixed spinel is a substantially better electrocatalyst. It is proposed that the differences arise from an enhanced rate of O-O bond cleavage early in the reduction process at NiCo 2 O 4 .

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

“…Moreover, the substitution of cobalt atoms by nickel leads to an enhancement of ORR kinetics. The results obtained with Co 3 O 4 /RGO_GO and NiCo 2 O 4 /RGO_GO catalysts confirmed earlier reports . As already reported, the cleavage rate of O−O bond is the rate‐determining step for spinel catalysts and this step is faster with NiCo 2 O 4 than with the Co 3 O 4 material .…”

“…The results obtained with Co 3 O 4 /RGO_GO and NiCo 2 O 4 /RGO_GO catalysts confirmed earlier reports . As already reported, the cleavage rate of O−O bond is the rate‐determining step for spinel catalysts and this step is faster with NiCo 2 O 4 than with the Co 3 O 4 material . As mentioned, cobalt substitution by nickel in cobaltite materials leads to the insertion of Ni atoms at octahedral sites.…”

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

“…at 0.85 V but approximately one order of magnitude lower than values from RRDE studies at 0.90 V in alkaline electrolyte reported as SA=320 μA cm −2 Pt and MA=150 A g −1 Pt . Deviations might occur due to the poorly controlled O 2 ‐mass transport in these measurements based on thick porous catalyst layers and packing of particles might reduce the surface area . The Tafel slopes b of Pt/C samples resulted in reasonable values of around 56 b /mV at low current densities indicating a dissociative mechanism.…”

“…Their activity can be improved by addition of carbon supports and structural design of the catalyst morphology . In addition, the substitution of Co atoms by another transition metal leads to an enhanced oxygen reduction activity . Wei et al .…”

“…In their comprehensive study they showed an enhanced activity for spinels in the order Co 3 O 4 <NiCo 2 O 4 <MnCo 2 O 4 . Similarly, Sönmez et al . showed a superior activity of NiCo 2 O 4 compared to that of Co 3 O 4 .…”