Exploring Conditions That Enhance Durability and Performance of a Tubular Solid Oxide Fuel Cell Fed with Simulated Biogas

Tubular solid-oxide fuel cells (t-SOFCs) fed directly with biogas, an equiproportioned mixture of CH4 and CO2 produced by fermentation of organic waste, are subject to nonuniform thermal stresses due to internal dry reforming in the anode entrance region coupled with structure exfoliation due to coking, resulting eventually in cell rupture. The integral t-SOFC is of practical interest, although many laboratory studies are conducted in differential button cells. Guided by mechanistic understanding and a robust thermodynamic model, the operating temperature and biogas feed composition were explored experimentally in order to enhance durability and performance of the t-SOFC. Thus, a temperature of 900 °C, a feed CH4/CO2 ratio of 45/55, and a fuel utilization ≥25% were found to be optimal. The cell durability, performance, efficiency, and outlet gas composition at open-circuit voltage (OCV) as well as at different loads were found to be in accord with a thermodynamic analysis and mechanistic understanding based on a set of four independent overall reactions (ORs). It is shown that the OCV is independent of the chosen electrodic OR. In addition to single-tube experiments, a 5-tube SOFC pilot-unit was preliminarily tested as a step toward scale-up of this promising renewable energy technology.