Fabrication and characterization of microtubular solid oxide cells for CO2/CO redox operations

Abstract

Ni-cermet fuel electrode-supported microtubular solid oxide cells with single layer Sm0.2Ce0.8O1.9 (SDC) electrolyte and bilayer YSZ/SDC electrolyte are fabricated for CO2/CO redox operations, i.e., NiO–SDC/SDC/PrBaCo2O5+δ and NiO–SDC/YSZ/SDC/PrBaCo2O5+δ, respectively. The substrate fuel electrode features radially well-aligned microchannels, which are open at the inner surface of the substrate, enabling facile fuel/gas diffusion. With CO/CO2 mixture gas as fuel, the SOFC performance of the single layer electrolyte cell is significantly improved over the bilayer electrolyte counterpart. However, due to the current leakage through the SDC electrolyte, the Faraday efficiency of the single layer electrolyte cell in SOEC mode is < 14%, even though the input current is very high at a given applied cell voltage, while the bilayer electrolyte cell may achieve Faraday efficiencies of 90% and above. Other different behaviors are also identified between the two cells. The study also emphasizes the important role of a purely ionic conducting electrolyte for CO2 electrolysis operation with microtubular cells. The substrate NiO–SDC electrode is fabricated using dual-layer spinning extrusion process in combination with phase inversion method. After heat treatment, the substrate electrode features radially well aligned microchannels, open at the inner surface. Built upon substrate electrode, dense and thin film electrolyte layer as well as oxygen electrode layer are fabricated through dip-coating and sintering alternatively, forming microtubular solid oxide cells. CO2/CO redox operations with the fabricated microtubular cells are systematically studied.