Photoelectrochemically converting CO2 over Z-scheme heterojunction CoPc/K7HNb6O19 with high Faraday efficiency

Photoelectrochemically converting CO2 into the high value-added chemicals and fuels is a hopeful sustainable energy conversion and storage road to alleviate the energy crisis and global warming. In this study, CoN-x Z-scheme heterojunctions were prepared by coupling CoPc with K7HNb6O19 rich in oxygen vacancy with a low-temperature calcination, and used for photoelectrocatalytic (PEC) reduction of CO2 to CO. The prepared heterojunctions demonstrate Faraday efficiency of −90 % and TOF values over a wide voltage range (−0.65 ∼ −1 V vs. RHE). The superior PEC CO2 reduction performance is mainly attributed to the designed Z-scheme heterojunction, which endows a built-in electric field to the interface of the two semiconductors, benefiting the separation of electrons and holes greatly. Additionally, the oxygen vacancies from K7HNb6O19 provide an alternative pathway for CO2 adsorption and activation, and simultaneously the incorporated K7HNb6O19 inhibits the aggregation of cobalt phthalocyanine molecules, which is beneficial for the stability of PEC catalysts. Density-functional-theory (DFT) calculation also elucidates a favorable CO2 activation energy over CoPc coupling oxygen-vacancy-rich K7HNb6O19 heterojunctions. This work may provide a viable pathway for the rational designing of efficient PEC systems to reduce CO2 to valuable fuels.