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 π-π 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 (TOF_CO ) of 2.7 s^-1 . Extending the photoelectrocatalysis to 10 h, a remarkable turnover number (TON_CO ) of 57000 was obtained. The high performance shown here is substantially improved from the previously reported photocathodes relying on covalently anchored catalysts.