Re-evaluating the Contribution of a Fe-Based Current Collector to Bioelectrochemical Methanogenesis: Role and...

The metal-based current collector has been adopted as an essential component of cathodes for electron delivery in microbial electrosynthesis (MES) cells, while the effect of its corrosion on biofilm development and electromethanogenesis activity was overlooked. In this study, the corrosion of the Fe-based current collector was identified to in situ decorate cathode naturally which substantially boosted the performance of CO₂ electromethanogenesis in terms of taking over two-thirds less time starting up MES and increasing the CH₄ production rate by 3.5 times. Despite the low concentration of Fe (0.13 at%), the electrochemical analysis indicated that it was possible for these Fe deposits to act as electron shuttles and catalysts for H₂ production to benefit methanogenesis. The Fe aggregates weakened the dependence of methanogens on electroactive bacteria (EABs) to conduct methanogenesis via interspecies electron transfer as the proportion of EABs on Bio FeCF (with Fe current collector, where CF is carbon felt) was only 25.5% of that on Bio CF (without Fe current collector). On the contrary, the abundance of genes encoding the proteins to uptake extracellular electrons of methanogens on Bio FeCF was 2.3 times higher than that on Bio CF. The enhanced energy transfer maintained high amounts of methanogens and live microorganisms. This study comprehensively explored the multiple roles of Fe-based current collectors in enhancing CO₂ electromethanogenesis.