Sensitivity of nickel cermet anodes to reduction conditions

The direct use of methane as fuel for solid oxide fuel cell (SOFC) without pre-reforming would reduce running costs and enable higher efficiencies. But methane generally causes carbon deposition on the nickel anode and subsequent power degradation. This paper shows that carbon deposition from methane is very sensitive to anode reduction conditions. The effect of direct methane on microtubular SOFC reduced at two different conditions was studied at temperatures above 800 °C. Reducing the cells at high temperature gave good performance on hydrogen but the current degraded quickly on methane, suggesting that carbon was blocking the nickel surfaces. This was not recoverable by bringing in hydrogen to replace the methane. Cells reduced under low temperature conditions gave higher current on methane than on hydrogen, showing that carbon deposited from the methane improved nickel anode conductivity in this case. These cells also did not degrade on methane under certain conditions but lasted for a long period. Extracting the carbon by feeding the cell with hydrogen interrupted this newly formed linkage between the nickel particles, reducing the electrical conductivity, which could be recovered by reintroducing methane. The conclusion was that nickel cermet anodes are very sensitive to reduction conditions, with low temperature reduction being preferred if methane is to be used as the chosen fuel.