Ni–LnOx (Ln = Dy, Ho, Er, Yb and Tb) cermet anodes for intermediate-temperature solid oxide fuel cells

Ni–LnOx (Ln = Dy, Ho, Er, Yb and Tb) cermets are investigated as the anodes of intermediate-temperature solid oxide fuel cells using ceria-based electrolyte to seek insights into the properties and electrocatalytic activity of these lanthanide oxides, whose oxygen ion conductivity is negligible. They have displayed similar electrochemical activity which is comparable to, if not higher than, those of the commonly Ni-doped ceria cermets. The anode performance has been found to depend strongly on cermet composition and porosity. Temperature programmed reduction study and EIS analysis under different hydrogen partial pressure suggest that the catalytic activity of the Ni–LnOx cermets might be originated from the hydrogen adsorption ability on the LnOx surface, promoting hydrogen spillover process, and consequently enhancing the electrochemical oxidation of the fuel.

If a anode consists of an oxide with negligible oxygen-ion conductivity, the H2 oxidation reaction is limited to the physical interface between the electrolyte and Ni, where the H2, Ni, and SDC electrolyte phases meet, i.e. path A. Accordingly, it is reasonable to consider that the high performance of Ni–LnOx (Ln = Dy, Ho, Er, Yb, Tb) anodes is only related to the high catalytic activity of LnOx. Temperature programmed reduction shows that the catalytic activity might originate from its capability of hydrogen adsorption. The presence of Ni/LnOx might promote hydrogen spillover processes, and consequently, enhance the electrochemical oxidation of the fuel. This reaction mechanism via the spillover process is illustrated by the reaction path B.Figure optionsDownload as PowerPoint slideHighlights
► LnOx (Ln = Dy, Ho, Er, Yb, Tb) are firstly investigated as the ceramic components in Ni-based cermet anodes for SOFCs.
► The high performance might be caused by LnOx capability of hydrogen adsorption.
► Hydrogen adsorption capability is as important as oxygen-ion conductivity for the ceramic component in a composite anode.