Co-Electrolysis of Steam and Carbon Dioxide in Solid Oxide Cells

Abstract

Reduction of H2O and CO2 as well as oxidation of H2 and CO was studied in a Ni/YSZ electrode supported Solid Oxide Cell (SOC) produced at DTU Energy conversion (former Risø DTU). Even though these Ni/YSZ based SOCs were developed and optimized for fuel cell use, they can work as reversible SOCs in mixtures of H2O, H2, CO2 and CO. From polarization (i-V) and electrochemical impedance spectroscopic characterization, it is evident that, electrochemical reduction of both CO2 and H2O occurs during co-electrolysis of H2O and CO2 in these Ni/YSZ based SOC. During co-electrolysis, the equilibrium of the water gas shift reaction is reached, and CO is therefore produced via the water gas shift reaction also. Significant differences during oxidation/reduction in H2O – H2 and CO2 – CO mixtures were observed implying that different reaction mechanisms apply for the mixtures.