In　a　microbial　electrolysis　cell　(MEC),　the　oxidization　of　organic　compounds　is　facilitated　by　an　electrogenic　biofilm　on　the　anode　surface.　The　biofilm　community　composition　determines　the　function　of　the　system.　Both　deterministic　and　stochastic　factors　affect　the　community,　but　the　relative　importance　of　different　factors　is　poorly　understood.　Anode　material　is　a　deterministic　factor　as　materials　with　different　properties　may　select　for　different　microorganisms.　Ecological　drift　is　a　stochastic　factor,　which　is　amplified　by　dispersal　limitation　between　communities.　Here,　we　compared　the　effects　of　three　anode　materials　(graphene,　carbon　cloth,　and　nickel)　with　the　effect　of　dispersal　limitation　on　the　function　and　biofilm　community　assembly.　Twelve　MECs　were　operated　for　56　days　in　four　hydraulically　connected　loops　and　shotgun　metagenomic　sequencing　was　used　to　analyse　the　microbial　community　composition　on　the　anode　surfaces　at　the　end　of　the　experiment.　The　anode　material　was　the　most　important　factor　affecting　the　performance　of　the　MECs,　explaining　54–80　%　of　the　variance　observed　in　peak　current　density,　total　electric　charge　generation,　and　start-up　lag　time,　while　dispersal　limitation　explained　10–16　%　of　the　variance.　Carbon　cloth　anodes　had　the　highest　current　generation　and　shortest　lag　time.　However,　dispersal　limitation　was　the　most　important　factor　affecting　microbial　community　structure,　explaining　61–98　%　of　the　variance　in　community　diversity,　evenness,　and　the　relative　abundance　of　the　most　abundant　taxa,　while　anode　material　explained　0–20　%　of　the　variance.　The　biofilms　contained　nine　Desulfobacterota　metagenome-assembled　genomes　(MAGs),　which　made　up　64–89　%　of　the　communities　and　were　likely　responsible　for　electricity　generation　in　the　MECs.　Different　MAGs　dominated　in　different　MECs.　Particularly　two　different　genotypes　related　to　Geobacter　benzoatilyticus　competed　for　dominance　on　the　anodes　and　reached　relative　abundances　up　to　83　%.　The　winning　genotype　was　the　same　in　all　MECs　that　were　hydraulically　connected　irrespective　of　anode　material　used.　©　2023　The　Authors