Charge accumulation processes in molecules for the production of H2 and the depletion of CO2

What is it about?

This work investigates how electrons generated by light absorption in a photo-absorbing semiconductor are transferred and accumulated in molecules immobilised at the surface of the semiconductor. In particular, we measure the speed and efficiency of the accumulation process as a function of the light intensity and the electrical applied potential. We find that the accumulation of more than one electron is relatively slow (around milliseconds) compared to the accumulation of only one electron (under microseconds), and it is highly sensitive to the light and potential conditions.

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Photo by Alex Dukhanov on Unsplash

Photo by Alex Dukhanov on Unsplash

Why is it important?

Because of the intermittency and low energy density of renewable energy and electricity, it is necessary to find cost-effective clean-energy storage solutions. One of the most promising approaches is based on converting renewable electricity into fuels such as H2, or into valuable chemicals from CO2, waste or biomass. All these electro-chemical reactions require the accumulation of more than one charge at a relatively small spot and their transfer to the reactants (i.e., water, CO2, etc.) The latter processes are usually mediated by a transition-metal based catalyst, which minimizes their energetic cost and facilitates the formation of chemical bonds. The working mechanism of the catalysts, however, is usually not well understood because of the fast pace of the reaction steps and the multiple reaction pathways. In this work, we have provided a unique glimpse into a very elusive reaction step (i.e., charge accumulation) with time-resolved and photoelectrochemical techniques.