Solar Fuels: Photoelectrosynthesis of CO from CO2 at p-Type Si using Fe Porphyrin Electrocatalysts

Photoelectrocatalytic conversion of CO2 to CO can be driven at a boron-doped, hydrogen terminated, p-type silicon electrode using a meso-tetraphenylporphyrin FeIII chloride in the presence of CF3CH2OH as a proton source and 0.1 M [NBu4][BF4]/MeCN/5 % DMF (v/v) as the electrolyte. Under illumination with polychromatic light, the photoelectrocatalysis operates with a photovoltage of about 650 mV positive of that for the dark reaction. Carbon monoxide is produced with a current efficiency >90 % and with a high selectivity over H2 formation. Photoelectrochemical current densities of 3 mA cm−2 at −1.1 V versus SCE are typical, and 175 turnovers have been attained over a 6 h period. Cyclic voltammetric data are consistent with a turnover frequency of equation image=0.24×104 s−1 for the photoelectrocatalysis at p-type Si at −1.2 V versus SCE this compares with equation image=1.03×104 s−1 for the electrocatalysis in the dark on vitreous carbon at a potential of −1.85 V versus SCE