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 under visible light illumination at low applied potential and high faradaic efficiency toward methanol. Several experimental reports suggest that aromatic amines such as pyridine (Py) are essential to the catalysis but the reaction mechanism leading to CO2 reduction in this system is still under debate. We use first-principles quantum mechanics with both periodic slab and embedded cluster calculations to investigate the catalytic mechanism on the GaP(110) surface. We initially proposed that the active catalyst in the system could be adsorbed dihydropyridine (DHP*), formed by surface hydride transfer (H-*) to adsorbed Py. However, we subsequently found that the proposed mechanism, indeed any mechanism involving desorption of hydride, to be kinetically hindered. We thus conclude that an intermediate whose formation does not require H-* transfer must play the role of the active co-catalyst. We then investigated adsorbed deprotonated dihydropyridine (2-PyH-*) as an alternative catalytic intermediate. We recently found that its formation is thermodynamically favored on various semiconductor electrode surfaces active towards CO2 reduction. Here we present the full energetics for 2-PyH-* formation and reaction with CO2 on the GaP(110) surface and show that these processes may be feasible on the illuminated surface.

First-principles investigation of adsorbed hydrogenated N-heterocycles as hydride shuttles for catalytic CO2 reduction on p-GaP photoelectrodes

255th National Meeting (2018)

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