Rational design and comparative studies of catalysts rely on detailed information about the mechanism of catalysis that in most cases is not available. We have used time-resolved UV/VIS and mid-IR spectroscopy to resolve highly reactive catalyst intermediates on the nano- to millisecond time scale, elucidate their structures and measure their reactivity in proton- and electron transfer reactions of the mechanistic cycle. Inspired by many enzymes that demonstrate exquisite control on PCET reactions, the introduction of proton relays in the secondary coordination sphere of catalysts has become a popular strategy, aiming to facilitate protonation and deprotonation. The azadithiolate bridge of FeFe-hydrogenase active sites have been taken as an example design for proton shuttling to the metal centre. Using direct spectroscopy measurements, we have recently shown that for the corresponding model complexes, the aza-group has no role as proton shuttle in the FeIFe0 state, as had been proposed. Instead, the effect of aza protonation is to shift the catalyst reduction potential, surprisingly with no or only little reduction in the rate of subsequent protonation. We have also been able to follow the charge transfer dynamics in catalyst-semiconductor systems. We show that the catalytic mechanism changes with varying conditions, both in solution and when immobilized on mesoporous semi-conductor surfaces.

Capturing intermediates of solar fuels catalysis by transient mid-IR spectroscopy

2019 Spring National Meeting

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