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

Abstract

Cobalt-based transition metal oxides are promising candidates for the oxygen evolution reaction.However, a complex interplay between the catalyst crystal structures and material morphologies as well as the surface reactions hampers a comprehensive understanding of the electrocatalytic oxygen evolution reaction at those materials. Here, we investigate the amount and reactivity of specific surface sites of a mesostructured cobalt oxide spinel powder by surface interrogation mode of scanning electrochemical microscopy (SI-SECM). The powder material was supplied in cavity-microelectrodes and efficiently titrated with an Fe(II)-triethanolamine redox mediator generated at a gold microelectrode in alkaline electrolyte. Thus, quantification of different surface sites was achieved and their reactivity showed dependence on the cobalt oxidation state.Titration experiments after adjustable time delays with respect to the generation of the different surface sites indicated that these surface sites are active for the oxygen evolution reaction. Kinetic analysis revealed two pseudo-first order decay constants that were related to fast and slow surface sites for the oxygen evolution reaction. Rate constants were determined for potentials where predominantly a mixed-valence Co III/IV state might be present as most active species. These results expand the great potential of the surface interrogation mode on studying the reaction kinetics of distinct surface sites for practically relevant powdered, non-precious metal catalysts to address a highly relevant challenge in electrocatalysis.

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

“…SI-SECM provides relevant mechanistic and kinetic information, which is not easily accessible by other spectroscopic and voltammetric techniques . The SI-SECM mode is widely employed for the study of OER electrocatalyst surfaces, because it enables the identification of different active sites within the same OER catalyst, the quantification of short-lived reaction intermediates, , the detection of different surface metal oxidation states and the calculation of kinetic rate constants of the active sites .…”

Descriptive Role of Pt/PtOx Ratio on the Selective Chlorine Evolution Reaction under Polarity Reversal as Studied by Scanning Electrochemical Microscopy

“…Up to recently, scanning electrochemical microscopy (SECM) utilizing the ultramicroelectrode (UME) tip came into the spotlight by either the feedback or redox competition mode for ClER characterization. − Compatibility with variable tip/substrate sizes and three-dimensional movement of the UME provided information on not only spatial activity variations but also operational flexibility to adjust ohmic resistance, capacitive current, and collection efficiency. More importantly, surface interrogation SECM (SI-SECM) could quantify adsorbed transient intermediate species such as OER intermediates for a wide range of surface coverages down to 3%, ,,− active sites at spinel metal oxide catalysts, and adsorbed hydrogen . The in situ analysis based on time-dependent feedback current strongly depends on selection of a suitable mediator.…”

Surface Interrogation of Electrodeposited MnOx and CaMnO3 Perovskites by Scanning Electrochemical Microscopy: Probing Active Sites and Kinetics for the Oxygen Evolution Reaction

“…1 mst ime resolution. SI-SECM has recently been used in investigations of catalysts for the hydrogen evolution, [22,23] water oxidation, [24][25][26][27] and oxygen reduction reactions. [28,29] Theredox behavior of surface manganese sites in electrodeposited MnO x and CaMnO 3 catalysts is investigated by SI-SECM.…”