Energy storage and syngas production by switching cathode gas in nickel-yttria stabilized zirconia supported solid oxide cell

Abstract

Energy storage is needed for the renewable energy power, and it is highly promising to convert CO2 to fuels utilizing the surplus renewable energy. Solid oxide cell (SOC) is an efficient energy conversation device, and it can realize energy storage by reversible operation. However, the CO2 electrolysis process is limited by the intensive energy input and low efficiency. To improve the electrolysis efficiency and realize syngas production, in this work, nickel-yttria stabilized zirconia (Ni/YSZ) supported solid oxide cell has been used for CH4 assisted CO2 electrolysis (CH4-SOEC). Moreover, a novel energy storage concept by cycling operating the cell in CH4-SOFC mode (discharge) and CH4-SOEC mode (charge) has been proposed, called CH4 assisted solid oxide cell (CH4-SOC). Besides energy storage, the CH4-SOC technology can realize syngas production as well. In the experiments, CH4 is continuously supplied to the Gd-doped ceria (GDC) modified Ni/YSZ anode, while air/CO2 are supplied to the YSZ-La0.6Sr0.4FeO3−δ (LSF)/GDC cathode in discharge/charge cycles, respectively. Experiments demonstrate that the cell presents well electrochemical performance and durability for 400 h under different operation modes. Using distribution of relaxation times (DRT) method, the rate limiting steps of the fundamental electrochemical processes in the electrodes have been identified. Moreover, thermodynamic calculations have been performed to evaluate the cell efficiency. Results suggest that the cell could realize an energy conversion efficiency of 84% in case of fuel utilization of 0.9, where the ratio of the discharge electric energy to the charge electric energy is about 0.95. Both experiments and calculations demonstrate the feasibility of technology, and using a conventional SOC is much important for the real application of it.