Controlling the fate of atomic H in photocatalytic reduction reactions is paramount to improve overall efficiency and limit unfavorable H2 evolution in CO2 upgrading and NH3 synthesis efforts. Working within the established framework of excited states driving surface chemistry via reduction and oxidation events has shown that selectivity towards H2 is often very high and not straightforward to limit through band gap or band edge alignment tuning. On the other hand, we have discovered a new pathway forward that involves a hydrogen transfer mechanism that is orders of magnitude more selective towards hydrogenation vs. H2 evolution. This new hydrogen transfer mechanism is associated with ground-state neutral atomic H and driven by high energy electron-phonon coupling effects. Instead of performing proton reduction with excited electrons, they may relax and produce high energy phonons that selectively excite surface-bound intermediates. This is an unusually mass-selective phenomenon that selectively excites elements with low atomic mass funneling energy to surface reactions. The inherently greater degrees of freedom at the catalyst surface also aid in funneling energy to surface reactions. Unlike classic photocatalysis, this phenomenon is promoted by elevated temperature and may be developed to operate in the strong electron-phonon coupling regime where phonon excitation is considerably coupled to photoexcited electrons. This phenomenon also allows for a plethora of energy at the surface of the catalyst such that energetically demanding reaction steps can be driven forward effectively. We will highlight our studies of photocatalytic CO2 reduction by H2O and light only and the need for new catalytic materials with rationally designed electron-phonon coupling structures. The effect of photocatalyst surface chemistry is also very pronounced in this catalysis lending yet another tunable parameter that must be freshly understood in the light of high energy catalytic surface chemistry. The discovery of this phenomenon may also enable dramatic progress in plasma-assisted catalysis. Strong electron-phonon coupling between a plasma and an appropriate catalytic material may allow the elevated energy of the plasma to directly participate in surface reactions rather than simply produce gas phase intermediates that collect and convert thermally on the catalyst surface.

New hydrogen-transfer mechanism driven by electron-phonon coupling that is selective towards hydrogenation in photocatalytic reduction reactions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.