Organic Redox Probes for the Key Oxidation States in Mixed Valence Ruthenium Oxide/Cyanometallate (Ruthenium Prussian Blue Analogue) Catalysts

Abstract

The electrochemical redox behavior of the polynuclear mixed valence ruthenium oxide cyanometallate complexes (mvRuOxÀMCN, M Fe, Cr, Ni, Cu, Ru and Pt) have been systematically studied in this report by using three redox sensitive organic probes of glucose, ethanol and formaldehyde. The results were interpreted by the well-established ruthenium oxide and Prussian blue chemistry. The mvRuOxÀMCN, under the category of Ru-based Prussian blue analogue, was found to possess superior electrocatalytic activity than either ruthenium oxide or Prussian blue in acidic mediums. The electrogenerated oxy/hydroxy-Ru VII state (at 1.1 V vs. Ag/AgCl) was unusually stabilized in the mvRuOxÀMCN matrix without any disproportion reaction in acidic environments. In contrast to those of earlier studies, possible structure in terms of the ÀRu III/II ÀNCÀMÀand ÀRu III/II ÀOÀRu VII/VI Àsites was proposed here. Enzymeless analytical detection of glucose in acidic conditions was first time demonstrated with sensitivity comparable to that of ruthenium oxide-based electrodes in alkaline solutions.

Development of an Enzymeless/Mediatorless Glucose Sensor Using Ruthenium Oxide‐Prussian Blue Combinative Analogue

“…Ultimately, the nature and direction of the sweep rate is very critical to achieving the unusual ruthenium oxidation state and thus catalysis. It is noteworthy that in our recent investigation with the mvRuOx-FeCN film did not show any such crossover reaction and the potential dependent redox current values [34]. It is obvious from the XPS that the mvRuOx-FeCN material is oriented with less amount of oxy and/or oxyhydroxy surface functional groups (O 1s response) and in turn to the poor Ru VII stabilization.…”

“…We recently investigated the pH effect (pH 2 -8) on a mvRuOx-FeCN/GCE system [34], and the A2/C2 catalytic peak current at ca. 1.05 V was found to start to sharply decrease from pH 2 !…”

“…3) and can thus partly validate this expectation. Since the mvRuOxRuCN film showed the highest sensitivity for glucose oxidation, it was chosen for the subsequent catalytic studies [34].…”

“…To emphasize the combined structure and properties of RuOx and PB, henceforth the RuMCN will be designated as mvRuOx-MCN [34]. Earlier, Cox and co-workers reported a mixed valent ruthenium oxide-cyanometallate complex for analytical sensing of alcohols, aldehydes, and nitroamines except carbohydrates, e.g., glucose [23,25,27,31].…”

“…The catalytic mechanism is also unknown. Recently, our preliminarily attempt on the redox sensitive organic redox probing (glucose, ethanol, and formaldehyde) analysis on RuOx and mvRuOx-FeCN indicated an unusual oxidation state of the RuOx-PB based combinative material [34]. Since both alcohols and aldehydes can be easily oxidized at RuOx electrodes in wide pH range (1 -14) [35 -38], we thus suspect that a specific form of RuOx present in the zeolite-PB network may cause the desired electrocatalytic performance.…”