Autotrophic hydrogen-producing biofilm growth sustained by a cathode as the sole electron and energy source

• Autotrophic H2-producing biofilm growth was sustained by a cathode at − 0.5 V vs SHE.
• Bioelectrocatalytic activity was sustained for a long period of time (> 1 year).
• 9.2 ± 1.3 L m− 2 day− 1 of hydrogen (1.88 A m− 2) was achieved at − 0.75 V vs. SHE.
• No H2-consuming microorganisms such as methanogens and acetogens developed.
• This represents a novel method for H2-producing electroactive bacteria enrichment.

It is still unclear whether autotrophic microbial biocathode biofilms are able to self-regenerate under purely cathodic conditions without any external electron or organic carbon sources. Here we report on the successful development and long-term operation of an autotrophic biocathode whereby an electroactive biofilm was able to grow and sustain itself with CO2 as a sole carbon source and using the cathode as electron source, with H2 as sole product. From a small inoculum of 15 mgCOD (in 250 mL), containing 30.3% Archaea, the bioelectrochemical system operating at − 0.5 V vs. SHE enabled an estimated biofilm growth of 300 mg as COD over a period of 276 days. A dramatic change in the microbial population was observed during this period with Archaea disappearing completely (< 0.1% of population). The predominant phyla enriched were Proteobacteria (57.3%), Firmicutes (12.4%), Bacteroidetes (11.6%) and Actinobacteria (1.1%). Up to 9.2 L H2 m− 2 day− 1 (1.88 A m− 2) was achieved when the cathode potential was decreased to − 0.75 V vs. SHE. This study demonstrates that purely autotrophic biofilm growth coupled to proton reduction to hydrogen alone can be sustained with a cathode as the sole electron source, while avoiding the development of H2-consuming microorganisms such as methanogens and acetogens.