Operation Of Solid Oxide Fuel Cells (SOFC) with Biogas Generated from Agri-Food Waste: Optimisation of Biogas Production and Analysis of Cell Performance

Due to the internal reforming that takes place in solid oxide fuel cells, they can operate with the (bio)methane contained in the biogas produced by anaerobic digestion (AD) from organic waste. In this sense, the potential of agri-food waste (onion skins) for biogas production and its use in SOFCs has been analyzed. For this purpose, physical, chemical, thermal, and combined pretreatments were tested on onion skins to increase the anaerobic biodegradability. The evaluated pretreatments increased the soluble chemical oxygen demand (SCOD). However, it was observed that the use of Ca(OH)₂ was preferred to NaOH, because it allowed the precipitation of sulphates, blocking the biological production of H₂S, which acts as a toxic compound for methanogenic archaea and as a catalytic poison of SOFC systems. This combination of pretreatments increased methane production by 36 and 19 % compared to untreated substrate. Once the most suitable pretreatment was identified, the biogas produced was used to feed a SOFC optimized by advanced ceramic processing to operate with this biofuel. The electrochemical performance of SOFC was examined through the characterization of I-VP and EIS curves for H₂ and the obtained biogas as fuels, operating at different temperatures: 800, 850, and 900 °C.