Redox-reversible iron orthovanadate cathode for solid oxide steam electrolyzer

Abstract

Solid oxide electrolyzers have demonstrated a tremendous advantage in the electrochemical conversion of H2O into H2 with high efficiencies by renewable electrical energy.[1-3] The high operation temperature leads to favorable kinetics and thermodynamics. The conventional Ni-YSZ (YSZ: 8% Y2O3 stabilized ZrO2) cathode has exhibited excellent steam-electrolysis performance under a reducing atmosphere however, the Ni-cermet is not redox stable and requires a significant concentration of reducing gas flowing over the Ni metal, avoiding the oxidation from Ni to NiO. Barnett et al. reported the high syngas yield of 7 sccm cm−2 with Ni-YSZ cathode from the coelectrolysis of CO2 /H2O with 25% H2 flowing in the cathode under 1.3 V at 800 ºC. [4] However, the Ni-cermets do display some disadvantages, such as reduction of three-phase boundaries (TPB) due to agglomeration after long operation and poor redox cycling causing volume instability.[5,6] The shortage of reducing atmosphere would not only breed the loss of electronic conductivity but also, in all probability, the mechanical failure of the Ni-YSZ cathode in the process of H2O electrolysis.[7].