Carbon formation on and deactivation of nickel-based/zirconia anodes in solid oxide fuel cells running on methane

Nickel/zirconia fuel reforming anodes in solid oxide fuel cells (SOFCs) running on methane have been studied using a test cell based on a tubular SOFC. The anodes have been characterised using temperature-programmed reduction (TPR) which reveals that two distinct types of nickel oxide are present in the anode prior to reduction. The steam reforming activity and surface chemistry of two different nickel/zirconia anode formulations and a molybdenum doped nickel/zirconia anode have been studied. All three show good activity towards methane steam reforming. It is found that the quantity of carbon deposited on the anode during methane reforming is strongly affected by the operating temperature and the methane/steam ratio. The addition of small quantities of molybdenum leads to a significant reduction in the amount of carbon deposited, whilst having little effect on the reforming activity or cell performance. Temperature-programmed oxidation (TPO) has revealed that three types of carbon are formed on the anodes during high temperature reaction of methane. As current is drawn from the cell, increased methane conversion occurs together with reduced carbon deposition, through reaction via partial oxidation and oxidative coupling with the flux of oxygen ions through the solid electrolyte. (C) 1998 Elsevier Science B.V. All rights reserved.