Influence of carbon filler content on the performance of SiOC/C electrodes for energy production in bio-electrochemical systems

Abstract

Silicon oxycarbide (SiOC) electrodes are emerging as alternatives to traditional carbon-based anodes in microbial fuel cells; however, their electrical conductivity remains low. To overcome this, carbon fillers are typically incorporated into the SiOC matrix, under the assumption that higher electrical conductivity enhances bio- electrochemical performance. Nevertheless, a systematic study on the effect of carbon filler content in SiOC/C electrodes has not been yet conducted, so this assumption requires validation. In this work, SiOC/C electrodes with varying micro-graphite (MG) contents and controlled porous architecture were developed. A positive exponential correlation between electrical conductivity and MG content was observed for the electrodes. When tested in bio-electrochemical cells, anode current densities at steady-state effectively scaled with the filler content, reaching maximum values when 20 or 30 wt% MG was used. However, the highest microbial growth rate and electrical charge provided were both strikingly achieved with 20 wt% filler, the overall bio- electrochemical performance being thus determined not only by electrical conductivity, but also by a proper balance of electrode surface roughness and the particular physiological stage during biofilm evolution. These findings suggest that the optimum carbon content in SiOC/C electrodes, leading to enhancing their bio- electrochemical performance, does not correspond to the highest electrical conductivity value.