Molecular catalysts offer a potentially high activity and selectivity for solar fuels production. Rational design of catalysts requires mechanistic understanding beyond overall performance measurements and benchmarking. By time-resolved laser spectroscopy reaction intermediates can be identified and their rates of interconversion can be determined.<br/> <br/>We have used a laser flash-quench method with time-resolved UV/VIS and mid-IR spectroscopy to induce rapid (~100 ns) reduction and protonation steps of molecular catalysts. In this way we can control single-electron reduction on a short time scale, and capture reactive intermediates that are not easily accessible by e.g. electrochemical methods. From the transient mid-IR spectra and comparison with calculated spectra, we could determine the structure of several intermediates of a photocatalytic proton reduction cycle for a series of [FeFe]-hydrogenase mimics. The results also show that the photocatalytic mechanism can be different from electrocatalytic mechanisms for the same catalyst, which illustrates the need for mechanistic understanding and underscores the problem of meaningful benchmarking of catalyst performance. The kinetics of hydride formation is compared, for complexes with and without internal acid/base groups as potential proton shuttles.<br/>

Capturing intermediates of molecular solar fuels catalysts by time-resolved mid-IR spectroscopy

253rd National Meeting (2017)

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