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.　©　2023　Science　Press　and　Dalian　Institute　of　Chemical　Physics,　Chinese　Academy　of　Sciences