Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 53: Focus Session: Electrocatalytic Energy Harvesting and Conversion

O 53.3: Topical Talk

Wednesday, March 9, 2016, 11:30–12:00, S052

Probing the Femtosecond Dynamics of the Hydrogen Evolution Reaction on Gold — •R. Kramer Campen, Francois Lapointe, and Yujin Tong — Fritz Haber Institute of the Max Planck Society, Berlin, Germany

While water electrolysis on gold electrodes was first demonstrated more than 225 years ago, the mechanisms of both the oxygen and hydrogen evolution halves of this process are still controversial. From an experimental point of view part of the challenge has been a lack of methods that allow characterization of transient intermediates. Here we report a novel experimental approach in which we initiate hydrogen evolution at a gold/liquid water interface using an intense, femtosecond, UV pulse to promote an electron from gold’s fermi level into water’s conduction band and track the fate of this electron with fs time resolution both optically, using interface specific sum frequency generation spectroscopy, and electrochemically via a double-pump, laser induced perturbation of the open circuit potential. The results of this approach suggest that, at circum-neutral pH, (i) at the gold/water interface the delocalized, conduction band, solvated electron has a lifetime of 150-250 fs depending on surface potential (ii) conduction band electrons relax to form localized solvated electrons the great majority of which have a potential dependent lifetime of 1-18 ps while a small fraction live for much longer, > 40 ps, and drive chemistry. These results furnish a potential-dependent, mechanistic picture of the transfer of electrons from gold into liquid water, the first step in hydrogen evolution.