Ruthenium Metallopolymer: Dawson Polyoxomolybdate α-[Mo₁₈O₅₄(SO₄)₂]^4– Adduct Films: Sensitization for Visible Photoelectrocatalysis

Abstract

Thin films of the adduct formed from the electrostatic association of the metallopolymer, [Ru(bpy)(2)(PVP)(10)](2+), and the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-), POMo, have been formed on ITO electrodes using an alternate immersion approach. The Ru/POMo ratio is 4.5:1, which exceeds the 2:1 ratio expected on the basis of the charges of the Ru(2+) and POMo(4-) building blocks. This behavior arises because of the polymeric character of the cation. In the presence of a substrate that has an abstractable proton such as benzyl alcohol, these ruthenium-sensitized polyoxomolybdate films generate significant photocurrents under visible irradiation. Significantly, increasing the surface coverage of the adduct from 1.4 × 10(-10) to 8.1 × 10(-10) mol cm(-2) does not measurably increase the photocurrent observed. Scan-rate-dependent cyclic voltammetry reveals that the rate of homogeneous charge transport through the film is slow, which most likely results in only a fraction of the film thickness being active for photoelectrocatalysis. The photocurrent increases markedly when the driving force for the oxidation of POMo(5-), created by the photoelectrocatalytic oxidation of benzyl alcohol, is increased. This result is consistent with the dynamics of heterogeneous electron transfer being centrally important to the regeneration of the photoelectrocatalyst. A system in which the surface coverage and applied overpotential are optimized produces a photocurrent density of 190 ± 18 nA cm(-2) under 480 ± 5 nm irradiation.

Photoelectrocatalytic Dioxygen Reduction Based on a Novel Thiophene-Functionalized Tricarbonylchloro(1,10-phenanthroline)rhenium(I)

“…These results proved that the photocurrents observed were cathodic. It is worth noting that the photocurrent (photocurrent density) observed at zero bias potential was found to be 1.6 µA (5.7 µA/cm 2 ), which compares favorably with those for most of the previously reported thin films [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]. Thus, we conclude that the film we studied here may be a highly promising candidate for applications in PEC oxygen reduction or sensing.…”

Facile assembly of polyoxometalate-polyelectrolyte films on nano-MO2 (M = Sn, Ti) for optical applications

“…3 Second, we have shown previously that the rate of charge transport through thicker films consisting of the polyoxometalate α-[S2Mo18O62] 4and a polycationic Ru(II) metallopolymer is slow due to mass transfer limitations, making thicker films less useful in photoelectrocatalytic applications (time to electrolyse whole film 2 -50 s). 4 In principle, low film conductivity can generally be addressed by either (a) increasing the supporting electrolyte concentration or (b) by incorporating conducting materials into the film -this has successfully been used in electrocatalytic applications using, for example, multi-walled carbon nanotubes. 5 However, for applications involving an optical component (photocatalysis, photoelectrochemistry, colorimetric sensing, electrochromic displays, photochromism) the addition of particulate or coloured materials into a film can, while rendering the film conducting, also significantly change its optical properties.…”

Visible Light-Driven Photoenergy Storage and Photocatalysis Using Polyoxometallates Coupled with a Ru Complex

“…Work that greatly pioneered the field is the development of dye-sensitized solar cells that are based on the TiO 2 /Ru complex system . In recent years, POMs such as α-SiW 9 O 34 and Mn 4 (H 2 O) 2 (VW 9 O 34 ) 2 were coupled with a Ru complex to split water into hydrogen and oxygen under visible light irradiation. , For photochemical applications, several other systems that combine POMs with Ru complexes have been reported. − Fay et al reported a visible-light-induced photoreduction of POMs in DMF using [Ru­(bpy) 3 ]­Cl 2 as a sensitizer . Attempts have also been made to intensively generate a reduced form of POMs for photoenergy storage using Ru or Ir complexes. , However, only a few studies have reported the reduction of POMs by visible light irradiation in organic solutions .…”