Enhanced sulfate reduction accompanied with electrically-conductive pili production in graphene oxide modified biocathodes.

•GO was reduced to graphene by sulfate-reducing biocathode.•Biocathode-reduced GO enhanced sulfate reduction and current output of MEC.•GO induced the production of electrically-conductive pili in biofilm.•It is the first time to observe highly conductive pili during GO reduction by SRB.