High-performance fuel electrodes based on NbTi0.5M0.5O4 (M = Ni, Cu) with reversible exsolution of the nano-catalyst for steam electrolysis

This paper investigates potential fuel electrode materials NbTi0.5M0.5O4 (M = Ni, Cu) for solid oxide steam electrolysers. Efficient catalytic metallic Ni and Cu nanoparticles are exsolved and anchor onto the surface of the highly electronically conducting material Nb1.33Ti0.67O4, forming an enhanced composite fuel electrode in the in situ reduction. The XRD, SEM, EDS and XPS results together confirm that the exsolution or dissolution of the nanometallic catalyst is completely reversible in the redox cycles. The electrical properties of the reduced NbTi0.5M0.5O4 ceramic fuel electrode is systematically investigated and correlated to the electrochemical performance of the composite fuel electrodes in symmetric cells or electrolysis cells. The synergetic effect of the metallic catalyst and ceramic fuel electrode leads to the excellent stability as well as the superior performance of the direct steam electrolysis without a flow of reducing gas over the composite fuel electrodes. The Faradic efficiencies of the steam electrolysis reach 95% and 97% for the Ni- and Cu-enhanced fuel electrodes on flowing reducing gas over the fuel electrodes, respectively, however, comparable performance is achieved for the direct steam electrolysis with Ni- and Cu-enhanced fuel electrodes without flowing reducing gas over the composite fuel electrodes.