Professor Leif Hammarström receives Presidential Award

Abstract from the award ceremony:

Molecular Mechanisms of Artificial Photosynthesis

Conversion of solar energy to a fuel requires a series of photo-induced charge separation steps that lead up to proton-coupled electron transfer (PCET) reactions at the catalysts for water oxidation and fuel formation. In natural photosynthesis and respiration, PCET is involved in a similar manner. PCET is required for levelling the potentials of the sequential catalyst redox steps. It also has substantial impact on the reaction rate, due to modulations of the reaction energy barrier as well as the strong dependence on the distance the proton has to tunnel during the reaction. For the design of efficient solar fuels production, and understanding of biological PCET, it is therefore necessary to understand and control PCET reactions.
The introduction of proton relays in the secondary coordination sphere of molecular solar fuels catalysts has become a popular strategy to accelerate catalysis. The exact mechanism behind the effects is often unclear, but assumed to be enhanced proton-tunneling probability in a PCET reaction. However, our work on some catalysts show that the supposed proton relay has no such function.

Instead, we use a metal-hydride catalyst model system and direct time-resolved observations to show that its proton-coupled oxidation could be accelerated by several orders of magnitude by an internal base that facilitates proton transfer.