title: Excess surface area in bioelectrochemical systems causes ion transport limitations.
abstract: We investigated ion transport limitations on 3D graphite felt electrodes by growing Geobacter sulfurreducens biofilms with advection to eliminate external mass transfer limitations. We characterized ion transport limitations by: (i) showing that serially increasing NaCl concentration up to 200 mM increased current linearly up to a total of +273% vs. 0 mM NaCl under advective conditions; (ii) growing the biofilm with a starting concentration of 200 mM NaCl, which led to a maximum current increase of 400% vs. current generation without NaCl, and (iii) showing that un-colonized surface area remained even after steady-state current was reached. After accounting for iR effects, we confirmed that the excess surface area existed despite a non-zero overpotential. The fact that the biofilm was constrained from colonizing and producing further current under these conditions confirmed the biofilms under study here were ion transport-limited. Our work demonstrates that the use of high surface area electrodes may not increase current density when the system design allows ion transport limitations to become dominant.
authors.affiliation: The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Harrington
authors.forename: Jerome T
authors.initials: JT
authors.lastname: Babauta
authors.forename: Emily K
authors.initials: EK
authors.lastname: Davenport
authors.forename: Ryan S
authors.initials: RS
authors.lastname: Renslow
authors.forename: Haluk
authors.initials: H
authors.lastname: Beyenal
mesh_terms: D001674:Bioelectric Energy Sources / Q000382:microbiology*; D018441:Biofilms / Q000254:growth & development; D004566:Electrodes; D004579:Electron Transport; D004867:Equipment Design; D045302:Geobacter / Q000502:physiology*; D006108:Graphite / Q000737:chemistry; D017136:Ion Transport; D010084:Oxidation-Reduction; D012965:Sodium Chloride / Q000378:metabolism
chemical_list: D012965:Sodium Chloride; D006108:Graphite
keywords: Geobacter sulfurreducens; bioelectrochemical system; biofilm; electron transfer; ion transport