Efficient photoelectrocatalytic CO2 reduction by cobalt complexes at silicon electrode

Abstract

Two homogeneous photoelectrocatalytic systems composed of simple polypyridyl Co complexes [Co(tpy)2](PF6)2 and [Co(bpy)3](PF6)2 as electrocatalysts and a Si wafer as the photoelectrode were used for combined photoelectrochemical reduction of CO2 to CO. A high photocurrent density of 1.4 mA/cm2 was observed for the system with the [Co(tpy)2](PF6)2 catalyst and a photovoltage of 400 mV was generated. Faradaic efficiencies of CO were optimized to 83% and 94% for the [Co(tpy)2](PF6)2 and [Co(bpy)3](PF6)2 complexes, respectively, in acetonitrile solution with 10% methanol (volume fraction, same below) as a protic additive. Addition of 2% water volume fraction induced a large amount of non-specific H2 evolution by the Si photoelectrode.