Is electron ping-pong limiting the catalytic hydrogen evolution activity in covalent photosensitizer–polyoxometalate dyads?

Abstract

Understanding the limitations of catalytic processes enables the design of optimized catalysts. Here, femtosecond transient absorption spectroelectrochemistry is used to explore the photophysics of polyoxometalate-based covalent photosensitizer-hydrogen evolution catalyst dyads....

Covalent Linkage of BODIPY‐Photosensitizers to Anderson‐Type Polyoxometalates Using CLICK Chemistry

“…The team demonstrated that variation of the central heterometal (Fe 3+ , Co 3+ , Mn 3+ ) of the Anderson anion can be used to tune the light‐driven hydrogen evolution of these systems. Further, detailed time‐resolved optical spectroscopy and spectro‐electrochemistry demonstrated the charge‐separation pathways [28] and identified limiting processes for the hydrogen evolution catalysis [29] …”

Multifunctional Polyoxometalate Platforms for Supramolecular Light‐Driven Hydrogen Evolution**

“…Thus, light-driven catalytic studies were performed in waterfree, de-aerated DMF solutions containing the respective catalyst POM-PtX (12.5 μM), the photosensitizer PS (125 μM) and triethyl amine/acetic acid (TEA (1.0 M)/HAc (0.2 M)) as sacrificial proton/electron donors; this experimental setup has been adapted from earlier POM-based HER studies. [48,[50][51][52] The samples were irradiated under an Ar atmosphere using monochromatic LEDs (λ max = 470 nm, P ~40 mW cm À 2 ) at 25 °C. Hydrogen evolution was quantified by calibrated gas chromatography.…”

Multifunctional Polyoxometalate-Platforms for Supramolecular Light-driven Hydrogen Evolution

“…PS was chosen due to its cationic charge, and the literature-known ability for light-driven electron transfer to POMs. 25,44 In addition, (spectro-)electrochemical analyses of both POM-PtX species showed, that at least two electron transfers from the photoreduced PS (E1/2 ca. -1.8 V vs. Fc + /Fc) 45 to POM-PtX is thermodynamically possible, as POM-PtX shows two redox-couples at potentials more positive than -1.8 V (see SI, Table S2, Figures S3, S4).…”

“…Thus, light-driven catalytic studies were performed in water-free, de-aerated DMF solutions containing the respective catalyst POM-PtX (12.5 µM), the photosensitizer PS (125 M) and triethyl amine/acetic acid (TEA (1.0 M) / HAc (0.2 M)) as sacrificial proton/electron donors; this experimental setup has been adapted from earlier POM-based HER studies. 44,[46][47][48] The samples were irradiated under an Ar atmosphere using monochromatic LEDs (λmax = 470 nm, P ~ 40 mW cm -2 ) at 25°C. Hydrogen evolution was quantified by calibrated gas chromatography.…”