RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

Debabrata Chatterjee,Maria Oszajca,Marta Chrzanowska,Rudi Van Eldik,Anna Katafias

doi:10.1039/d1ra03293c

Abstract

The reduction of molecular oxygen (O2) and hydrogen peroxide (H2O2) by [RuII(edta)(pz)]2− (edta4− = ethylenediaminetetraacetate; pz = pyrazine) has been studied spectrophotometrically and kinetically in aqueous solution. Exposure of the aqua-analogue [RuII(edta)(H2O)]2− to O2 and H2O2 resulted in the formation of [RuIII(edta)(H2O)]− species, with subsequent formation of the corresponding RuV Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O complex. A working mechanism for the O2 and H2O2 reduction reactions mediated by the RuII(edta) complexes is proposed. The role of the coordinated water molecule (by its absence or presence in the primary coordination sphere) in controlling the mechanistic pathways, outer-sphere or inner-sphere, is discussed.

Highlights

The electrochemical oxygen reduction reaction (ORR) proceeds by two-electron two-proton (2eÀ/2H+) partial reduction of O2 to produce H2O2 (eqn (1) in Scheme 1) or direct four-electron fourproton (4eÀ/4H+) reduction of O2 to 2H2O (eqn (3) in Scheme 1)
We report the results of the detailed spectral and kinetic investigation of the reduction of O2 and H2O2 by the above referred RuII(edta) complexes
The [RuIII(edta)(pz)]À complex can be reduced electrochemically (E1/2 value corresponding to the [RuIII(edta)(pz)]À/ [RuII(edta)(pz)]2À couple is 0.252 V vs. SHE)[19] or chemically[22] to its ruthenium(II) analogue, [RuII(edta)(pz)]2À (Fig. 1)

Summary

Introduction

The electrochemical oxygen reduction reaction (ORR) proceeds by two-electron two-proton (2eÀ/2H+) partial reduction of O2 to produce H2O2 (eqn (1) in Scheme 1) or direct four-electron fourproton (4eÀ/4H+) reduction of O2 to 2H2O (eqn (3) in Scheme 1). A er complete disappearance of the peak at 462 nm (attributed to the oxidation of the [RuII(edta)(pz)]2À to [RuIII(edta)(pz)]À) under the speci ed conditions (see Fig. 3a), the reaction is followed by a step that involves the formation of a band at 390 nm.

Results

Conclusion