Aqueous CO2 Reduction on Si Photocathodes Functionalized by Cobalt Molecular Catalysts/Carbon Nanotubes

Photoelectrochemical reduction of CO2 is a promising approach for renewable fuel production. We herein report a novel strategy for preparation of hybrid photocathodes by immobilizing molecular cobalt catalysts on TiO2-protected n(+)-p Si electrodes (Si|TiO2) coated with multiwalled carbon nanotubes (CNTs) by pi-pi stacking. Upon loading a composite of Co-II(BrqPy) (BrqPy=4 ',4 ''-bis(4-bromophenyl)-2,2 ' : 6 ',2 '' : 6 '',2 '''-quaterpyridine) catalyst and CNT on Si|TiO2, a stable 1-Sun photocurrent density of -1.5 mA cm(-2) was sustained over 2 h in a neutral aqueous solution with unity Faradaic efficiency and selectivity for CO production at a bias of zero overpotential (-0.11 V vs. RHE), associated with a turnover frequency (TOFCO) of 2.7 s(-1). Extending the photoelectrocatalysis to 10 h, a remarkable turnover number (TONCO) of 57000 was obtained. The high performance shown here is substantially improved from the previously reported photocathodes relying on covalently anchored catalysts.