Polyoxometalates as solution-phase electrocatalytic mediators for reduced electrode fouling and the improved oxidative response of phenols

• Polyoxometalates (POMs) can mediate the oxidation of phenolics.
• Typical phenol passivation of electrode is prevented by POM.
• Electrocatalytic mediation occurs by homogeneous oxidation of the phenoxyl radical.
• 11-fold increases in peak current possible, in the case of vanillin
• Exhaustive two-electron electrolysis of vanillin can even be performed.

The electrochemical oxidation of phenols typically passivates electrodes, due to the reactive one-electron oxidation intermediate, a phenoxyl radical cation. Here, we show that the addition of polyoxometalates to the electrolyte can prevent electrode passivation via an EC`E mechanism; the initial oxidation is unchanged, but oxidation of the phenoxyl radical intermediate is mediated. As such the electrochemistry assumes an ideal EE process, as confirmed by cyclic voltammetric simulation, with no electrode fouling on the voltammetric timescale. Bulk electrolysis of phenolic molecules can even be performed to isolate solution-phase products. This is exemplified by the scenario of vanillin (phenolic compound) and phosphotungstic acid (H3[PW12O40], a polyoxometalate).

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