Anodic polarization characteristics in hydrogen and methane oxidations at nickel-cobalt yttria-stabilized zirconia cermet relating to prolonged cell performance stability

Abstract

The conventional solid oxide fuel cell (SOFC) anode, which consists of metallic Ni and yttria-stabilized zirconia (YSZ), is liable to deactivation when a carbon-containing gaseous fuel is directly supplied. To retard the degradation due to a direct supply of CH4, the Ni/YSZ has been modified with the incorporation of Co into the Ni matrix, forming a substitutional solid-solution alloy. As a result, the porous anode exhibits well-connected compositional grains owing to the Co3O4 precursor as a sintering aid. The 25 mol% Co incorporation producing the Ni0.75Co0.25/YSZ anode significantly improves the cell performance and prolonged stability. In addition, the Ni0.75Co0.25/YSZ anode provides the apparent activation energy of the charge transfer reaction to a lower value in the electrochemical oxidation of CH4 at the triple-phase boundary. However, the apparent activation energy decrease is not identified for H2. The Co alloying effect on catalyzing the electrochemical oxidation of CH4 is caused by suppressing the carbon deposition originating from the thermal dissociation of adsorbed CH4 on the Ni1-xCox alloy surface.