Photo-coupled electrocatalytic conversion of CO2 to CO over cobalt phthalocyanine-modified POM-K8Ta6O19 Z-scheme photocathodes

Abstract

The construction of inorganic–organic heterojunctions, inspired by natural photosynthesis, is regarded as an effective strategy for designing highly efficient photoelectrocatalysts for CO₂ conversion. In this study, we successfully prepared Z-scheme heterojunction photoelectrocatalysts by loading cobalt phthalocyanine (CoPc) onto a substrate of K₈Ta₆O₁₉ crystals containing oxygen vacancies, a type of polyoxometalate (POM), using an impregnation method combined with low-temperature calcination. The results revealed that their CO₂ reduction to CO performance could be significantly enhanced under simulated-solar-photo-coupled electrocatalytic conditions. The optimal photoelectrocatalytic CO₂ reduction performance was achieved over CoT-7 (CoPc/K₈Ta₆O₁₉ mass ratio = 1 : 7), exhibiting a faradaic efficiency of 99.5% for CO (FE_CO) and a high CO production rate of ∼309 μmol cm⁻² h⁻¹ at −1.0 V vs. RHE, which is three-times higher than that of pure CoPc. The enhanced activity of the photocathodes was attributed to their broadened light absorption and efficient separation of photogenerated charges through the Z-scheme electron transfer pathway, which promoted electron transport and minimized charge carrier recombination. Moreover, the photoelectrocatalytic mechanism for this Z-scheme was also further expounded using collective experimental results such as X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, electrochemical tests and in situ infrared spectroscopy. This work provides a strategy for designing efficient Z-scheme heterojunction photoelectrocatalysts through inorganic–organic coupling.