Bi-Eu bimetallic catalysts enabling ultrastable electroreduction of CO2 with a ∼ 100% formate Faradaic efficiency

•Bi8Eu1 bimetallic nanoparticles were synthesized for CO2 electroreduction.•High formate FE (>97%) in a wide potential window (−0.89 ∼  − 1.19 VRHE).•Long-term stability of 400 h in H-type cell.•High current density of 250 mA cm−2 in flow-cell.•DFT calculations reveal that the Bi-Eu interactions benefit formate production.