Solar fuels: photoelectrosynthesis of CO from CO2 at p-type Si using Fe porphyrin electrocatalysts

Abstract

Photoelectrocatalytic conversion of CO2 to CO can be driven at a boron-doped, hydrogen terminated, p-type silicon electrode using a meso-tetraphenylporphyrin Fe(III) 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 k(Si)(obs)=0.24×10(4) s(-1) for the photoelectrocatalysis at p-type Si at -1.2 V versus SCE this compares with k(Si)(obs)=1.03×10(4) s(-1) for the electrocatalysis in the dark on vitreous carbon at a potential of -1.85 V versus SCE.

Keywords: CO2 reduction; iron; p-type silicon; photoelectrocatalysis; porphyrins.