Building efficient biocathodes with Acidithiobacillus ferrooxidans for the high current generation

The development of biocathodes is highly fascinating in microbial electrochemical technologies research. In this study, iron-oxidizing bacterium Acidithiobacillus ferrooxidans-based biocathodes were developed under the constant polarization of the electrochemical reactors at −0.2 V vs. Ag/AgCl with a pH of 2. On the 15^th day of the 21-day batch experiment, A. ferrooxidans-based biocathode produced a maximum current density of −38.61 ± 13.16 A m⁻² when the reactors were supplemented with 125 mM Fe²⁺ ions as an electron donor and 9 mM citrate as an iron chelator to buffer the iron-rich medium. Oxidation of Fe²⁺ to Fe³⁺ by A. ferrooxidans and its electrochemical regeneration at the cathode were mainly responsible for the high current generation. Furthermore, in the presence of iron, A. ferrooxidans develop a multi-layer biofilm on the cathode surface, which could potentially perform an indirect electron transfer mechanism.