Selectively converting CO2 to HCOOH on Cu-alloys integrated in hematite-driven artificial photosynthetic cells

The integration of electrochemical CO2 reduction (CO2RR) and photoelectrochemical water oxidation offers a sustainable access to valuable chemicals and fuels. Here, we develop a rapidly annealed hematite photoanode with a photocurrent density of 2.83 mA cm−2 at 1.7 VRHE to drive the full-reaction. We also present Cu-alloys electrocatalysis extended from CuInSnS4, which are superior in both activity and selectivity for CO2RR. Specifically, the screened CuInSn achieves a CO2 to HCOOH Faradaic efficiency of 93% at a cell voltage of −2.0 V by assembling into artificial photosynthesis cell. The stability test of IT exhibits less than 3% degradation over 24 h. Furthermore, in-situ Raman spectroscopy reveals that both CO32- and CO2 are involved in CO2RR as reactants. The preferential affinity of C for H in the *HCO2 intermediate enables an improved HCOOH-selectivity, highlighting the role of multifunctional Cu in reducing the cell voltage and enhancing the photocurrent density.