Selectively converting CO 2 to HCOOH on Cu-alloys integrated in hematite-driven artificial photosynthetic cells

The integration of electrochemical CO 2 reduction (CO 2 RR) 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 V RHE to drive the full-reaction. We also present Cu-alloys electrocatalysis extended from CuInSnS 4, which are superior in both activity and selectivity for CO 2 RR. Specifically, the screened CuInSn achieves a CO 2 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 CO 2 are involved in CO 2 RR as reactants. The preferential affinity of C for H in the *HCO 2 intermediate enables an improved HCOOH-selectivity, highlighting the role of multifunctional Cu in reducing the cell voltage and enhancing the photocurrent density.