Ruthenium metallopolymer: Dawson polyoxomolybdate alpha-[Mo18O54(SO4)(2)](4-) adduct films: sensitization for visible photoelectrocatalysis

Jie Zhu, James J Walsh, Alan Maxwell Bond, Tia E Keyes, Robert J Forster

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Abstract

Thin films of the adduct formed from the electrostatic association of the metallopolymer, [Ru(bpy)(2)(PVP)(10)](2+), and the Dawson polyoxomolybdate alpha-[Mo18O54(SO4)(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 Ru2+ and POMo4- 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 x 10(-10) to 8.1 x 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 POMo5-, 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.
Original languageEnglish
Pages (from-to)13536 - 13541
Number of pages6
JournalLangmuir
Volume28
Issue number37
DOIs
Publication statusPublished - 2012

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