Adapting microbial communities to low anode potentials improves performance of MECs at negative potentials

- Developed communities at 0 mV and −400 mV vs. Ag/AgCl for converting biomass-derived liquids.
- Electroactive community at −400 mV achieved a maximum current density of 12 A/m2.
- Lower set anode potential resulted in a 1.5-fold higher electrical efficiency.
- A maximum hydrogen productivity of 10.9 L-H2/L-anode-day was obtained.

A unique aspect of microbial electrolysis cells is the use of an applied voltage for H2 production. A variation on this parameter is the use of a controlled anode potential rather than controlled cell voltage, which can result in a more stable redox environment for the anode microbes. In this study, long-term exposure of anode consortia at −400 mV and 0 mV vs. Ag/AgCl resulted in a gradual divergence of the resulting bioanode midpoint potentials by >100 mV over a 6-month period. Cyclic voltammetry revealed a shift in peak current production to more negative potentials for the reactor poised at −400 mV. Furthermore, chronopotentiometry indicated very different profiles, showing a difference of 500 mV in the potential required to achieve a current of 15 mA (equivalent to 12 A/m2). A 3-fold higher current was observed at a poised potential of −400 mV for the anode enriched at a poised potential of −400 mV, compared to that enriched at 0 mV. The substrate used was a bio-oil aqueous phase (BOAP) derived from switchgrass, making this study unique with potential for biorefinery application in producing hydrogen, fuels or chemicals. Operation at −400 mV resulted in a 1.5-fold higher electrical efficiency reaching 164.9%, while marginally reducing hydrogen recovery by 1.0%. The results provide evidence for adaptation of complex communities to optimize applied potential, while reducing energy input for electrolysis. The community developed here has potential to be explored further to understand complex community-function relationships.

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