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

Abstract

Cobalt oxides are known as abundant and stable catalysts for the oxygen reduction reaction (ORR) in an alkaline environment. Here, the ORR activity of Co3O4 and mixed metal oxides NiCo2O4 and CuCo2O4 was studied. Synthesis by using the nanocasting procedure resulted in a mesostructured spinel phase with uniform morphology and high surface area. However, the evaluation of the specific activity of this material class is often hampered by limitations in determining the real surface area. The cavity‐microelectrode technique did not require the addition of any additives to the catalytic material. Thus, measuring the double layer capacitance was used to assess the surface area. This approach showed comparable and reliable values for all samples and different cavity depths. Furthermore, the in situ derived surface area enabled the determination of the specific ORR activity, which is more accurate than utilizing the geometric and nitrogen absorption derived surface area. Although the activity of Co3O4 was rather low, the presence of Ni2+ and Cu2+ in the mixed metal oxides led to a substantial activity enhancement, possibly by providing additional active sites.

Determining the Efficiency of Photoelectrode Materials by Coupling Cavity‐Microelectrode Tips and Scanning Electrochemical Microscopy

“…In addition to its fast screening features, the present method is not affected by any contribution from the supporting material (i. e. FTO or ITO) and of binders that might introduce artifacts: this is one of the most recognized features of C‐MEs …”

“…Other advantages of C‐ME, e. g. the precise control of the amount of powder loaded in the cavity, are well established, and the combined use with SECM was previously introduced as well in the case of high conductivity powders for the OER . The use of Au CM−E's filled with the studied material is equivalent to prepare custom microdisk tips, avoiding time consuming techniques for the preparation of microdisks of desired materials …”

Coulometric Titration of Active Sites at Mesostructured Cobalt Oxide Spinel by Surface Interrogation Mode of Scanning Electrochemical Microscopy

“…29,[35][36] Furthermore, a spinel-type Co 3 O 4 with a cubic structure replicated from the hard template was confirmed by X-ray diffraction measurements. 28 Particles of around 8 nm are highly ordered assembled to form the primary domain with the size between 100 and 500 nm (Figure S1b). The nanoparticles display clear lattice fringes with a spacing of 0.24 nm, which can be index to the (311) planes of Co 3 O 4 spinel (PDF: 00-042-1467) (Figure 1a).…”

“…The ordered mesoporous structure leads to a high specific surface area, which can be employed as a nice model system. [26][27][28] Cobalt-based materials are widely reported as bifunctional catalyst for both OER and ORR. [29][30][31] Their activity depends on the oxidation state of near-surface metal cations under applied electrode potential.…”

A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions: Nano-Co3O4-Deposited La0.5Sr0.5MnO3 via Infiltration

“…The focus in the literature has been on transition-metal oxides because oxygen electrocatalysts possess bifunctionality due to their operational stability in alkaline solutions and promising catalytic activities for ORR and OER. Among them, Co-containing oxides such as Co 3 O 4 , Ln x Sr 1- x CoO 3- δ , and Ba x Sr 1- x Co y Fe 1- y O 3- δ have especially been reported as efficient electrocatalysts for OER [ 13 , 16 , 17 , 18 , 19 , 20 , 21 ]. Mn-containing oxides (e.g., Mn 2 O 3 , NiMnO 2 , CoMnO 2 , and La 0.5 Sr 0.5 MnO 3- δ ) have demonstrated excellent catalytic activity for ORR [ 22 , 23 , 24 , 25 , 26 ].…”