High-power, high-energy solid oxide fuel cell using lignosulfonate as energy source and Fe2O3 as pseudo-fuel

Abstract Biomass, especially lignin, is a potential renewable and carbon–neutral energy resource. The present work developed a solid oxide fuel cell (SOFC) capable of converting lignosulfonate directly into electricity with high efficiency. The pyrolysis of lignin below 1000 °C typically generates tar and char, which are difficult to decompose. Hence, the use of lignin as fuel at 800 °C, the typical operating temperature of an SOFC, requires the accelerated anode reaction of such products. For this reason, various transition metal oxides were added to the anode as pseudo-fuels in this work. CuO, NiO and CoO were found to be reduced to their metallic states when employing a sodium lignosulfonate fuel under open circuit conditions, and these metals contributed little to the discharge reaction. In contrast, Fe 2 O 3 repeatedly cycled between a metallic state and FeO or Fe 3 O 4 during discharge, allowing for stable cell operation over a long period of time. The gravimetric energy density (Wh g –1 ) of the lignosulfonate fuel was also shown to increase with increasing fuel mass. This effect was attributed to an additional gasification reaction (the Boudouard reaction) in which tar and char reacted with CO 2 to form CO. This reaction was promoted as the lignosulfonate mass was increased. An optimized SOFC generated electrical energy equivalent to 18.3% of the higher heating value for the lignosulfonate fuel.