The development of efficient catalysts for the conversion of CO2 to liquid fuels is a main challenge of our age. Overcoming this challenge will provide us with a carbon-neutral and renewable energy source. A system consisting of a p-GaP electrode and a pyridine-based co-catalyst has been shown to reduce CO2 at low overpotentials and high faradaic efficiency toward methanol. The reaction mechanism leading to CO2 reduction in this system is still under debate. Experimental conditions suggest that pyridinium (PyH+) is essential to the catalysis. It has been proposed that PyH+ may be reduced to the pyridinyl radical which then reacts to form the active catalytic species for CO2 reduction. In this contribution, we use first-principles quantum mechanics with both periodic slab and embedded cluster calculations to investigate the fate and the role of PyH+. We show that PyH+ will not be reduced to the pyridinyl radical, even under illumination to produce photoexcited electrons in GaP. We instead propose an alternative, viable pathway for PyH+ reduction. This pathway leads to the formation of adsorbed pyridine and adsorbed hydrogen atoms; these species may react to form adsorbed dihydropyridine (DHP) which has been proposed to play the role of the active catalyst. Subsequently, we use cluster calculations to investigate whether the proposed reaction pathway for adsorbed DHP formation is thermodynamically and kinetically favored and whether this species can act as a co-catalyst for CO2 reduction on GaP electrodes.

First-principles investigation of the role of pyridinium and adsorbed dihydropyridine in pyridine-catalyzed CO2 reduction on p-GaP photoelectrodes

251st National Meeting (2016)

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