Mediator Enhanced Water Oxidation Using Rb₄[Ru^II(bpy)₃]₅[{Ru^III₄O₄(OH)₂(H₂O)₄}(γ-SiW₁₀O₃₆)₂] Film Modified Electrodes

Abstract

The water insoluble complex Rb4[Ru(II)(bpy)3]5[{Ru(III)4O4(OH)2(H2O)4}(γ-SiW10O36)2], ([Ru(II)bpy]5[Ru(III)4POM]), was synthesized from Rb8K2[{Ru(IV)4O4(OH)2(H2O)4}(γ-SiW10O36)2] and used for electrocatalytic water oxidation under both thin- and thick-film electrode conditions. Results demonstrate that the [Ru(II)bpy]5[Ru(III)4POM] modified electrode enables efficient water oxidation to be achieved at neutral pH using thin-film conditions, with [Ru(bpy)3](3+)([Ru(III)bpy]) acting as the electron transfer mediator and [Ru(V)4POM] as the species releasing O2. The rotating ring disc electrode (RRDE) method was used to quantitatively determine the turnover frequency (TOF) of the catalyst, and a value of 0.35 s(-1) was obtained at a low overpotential of 0.49 V (1.10 V vs Ag/AgCl) at pH 7.0. The postulated mechanism for the mediator enhanced catalytic water process in a pH 7 buffer containing 0.1 M LiClO4 as an additional electrolyte includes the following reactions (ion transfer for maintaining charge neutrality is omitted for simplicity): [Ru(II)bpy]5[Ru(III)4POM] → [Ru(III)bpy]5[Ru(V)4POM] + 13 e(-) and [Ru(III)bpy]5[Ru(V)4POM] + 2H2O → [Ru(III)bpy]5[Ru(IV)4POM] + O2 + 4H(+). The voltammetry of related water insoluble [Ru(II)bpy]2[S2M18O62] (M = W and Mo) and [Fe(II)Phen]x[Ru(III)4POM] materials has also been studied, and the lack of electrocatalytic water oxidation in these cases supports the hypothesis that [Ru(III)bpy] is the electron transfer mediator and [Ru(V)4POM] is the species responsible for oxygen evolution.

Electrocatalytic oxidation of water by a self-assembled oxovanadium(iv) complex modified gold electrode

“…Consequently, catalysts that allow electrochemical oxidation of water at low overpotential are of great interest. 4,5 Although precious metals can show high catalytic activity for water oxidation at low overpotential, the high cost prohibits their widespread use. 6,7 The creation of earth-abundant molecular systems that produce O 2 from water with high catalytic activity and stability thus remains a significant basic science challenge.…”

“…Several heterogeneous catalysts have been developed for electrochemical water oxidation; some of them are Mn-oxide thin films on a polished GC electrode, 22 Mn 3 O 4 -Au nanocomposites on a gold electrode, 23 hydrated metal oxide modified electrodes, 24 Fe-based films on an ITO electrode, 25 Co 3 O 4 nanoparticles 26 and [Ni 1−x Fe x IJOH) 2 ]IJNO 3 ) y IJOH) x−y •nH 2 O nanosheets on a flat HOPG surface, 27 cobalt polyoxometalate (POM) carbon paste electrodes, 28 cobalt-modified fluorinedoped tin oxide electrodes, 29 nickel oxyhydroxide thin films, 30 a [RuIJbpy) 5 ]ijRu 4 POM]-modified electrode, 4 iridium oxide-polymer composite electrodes, 31 carbon-grafted iridium complexes, 32 IrO 2 colloid self-assembled on an ITO electrode, 6 mesoporous IrO x nanoparticle films, 7 etc.…”

Electrochemical properties of the [SiW10O36(M2O2Kemmegne‐Mbouguen1, Floquet2, Cadot3 2021Comptes Rendus. Chimie6000View full textAdd to dashboardCite

“…In particular, with a tremendously diverse variety of POMs capable of storing a high number of electrons and displaying proton transfer capabilities, this class of compounds behaves as very efficient electrocatalysts for reactions of environmental interest such as CO 2 reduction [20][21][22], proton reduction into hydrogen [23][24][25], oxygen evolution reaction [26][27][28][29], or detection of environmental pollutants like nitrogen oxides [30][31][32][33][34][35], bromates [35][36][37][38], or iodates [35,37,[39][40][41].…”

Bioinspired Electrocatalytic CO2Reduction by Bovine Serum Albumin‐Capped Silver Nanoclusters Mediated by [α‐SiW12O40]4−

“…[14] Polyoxometalates (POMs), for example, [a-SiW 12 O 40 ] 4À , [15] are molecular oxide anionst hat undergo multiple reversible electroreduction processes covering aw ide potential range. Therefore, as uitable redox process can be chosen to provide the drivingf orce required for CO 2 reduction if aP OM is used as the electron transfer mediator.…”

“…cently by us to establish ar apid communicationp athway for am olecular catalyst in the solid state, which resultedi ns ignificantly enhanced catalytic activity for the electrooxidation of water. [14] Polyoxometalates (POMs), for example, [a-SiW 12 O 40 ] 4À , [15] are molecular oxide anionst hat undergo multiple reversible electroreduction processes covering aw ide potential range. Therefore, as uitable redox process can be chosen to provide the drivingf orce required for CO 2 reduction if aP OM is used as the electron transfer mediator.…”