The presentation describes a new type of low-cost and easy-to-fabricate mixed e^- and CO₃^2- conducting membrane for advanced high-flux and selective electrochemical CO₂ separation from flue gas. The membrane is consisted of a CO₃^2--conducting molten carbonate phase and an e^--conducting lithiated Ni-oxide interphase formed in situ during operation. The testing results explicitly show that the membrane exhibits a CO₂ flux density >1.0 mL min^-1 cm^-2 at 850 ^oC with a selectivity of 100-500 and excellent stability for 450 hours. Compelling experimental evidence is also provided to support that the self-formed interphase Li_0.4Ni_1.6O₂ is highly electronic conducting and responsible for providing electrons to the co-reduction of CO₂ and O₂ into CO₃^2-. Given the performance level demonstrated, this low-cost and easy-to-fabricate membrane is superior to the conventional “size-sieving” inorganic and “dissolution-diffusion” organic counterparts, promising it to be a very competitive technology for future advanced CO₂ capture from flue gas.