Electrical energy storage with engineered biological systems

Table 2 Overpotentials for a representative set of biological electron transfer systems

Microorganism	Reactions	Electron flow^a	Estimated applied electrode potential (V. vs. SHE)	Assumed acceptor^b	Estimated electrode overpotential (V)^c	Biofilm thickness (μm) or cell density (OD unit)	Cathode material	Electron transport mechanism	Reference
Geobactor sulfurreducens strain DL-1	Fumarate to succinate	Cathodic	-0.3	Mtr EET Complex	≈ 0.2	35	Graphite	EET	Ueki et al. [63]
Geobactor sulfurreducens	Fumarate to succinate	Cathodic	-0.3	Mtr EET Complex	≈ 0.2	12	Graphite	EET	Strycharz-Glaven et al. [139]
Geobacter sulfurreducens	Acetate to electricity	Anodic	0.3	Mtr EET Complex	≈ 0.4	40	Graphite	EET	Reguera et al. [140]
Sporomusa ovata	CO₂ to acetate	Cathodic	-0.4	Mtr EET Complex	≈ 0.3	12	Graphite	EET	Nevin et al. [141]
Mariprofundus ferrooxydans	Fe³⁺/Fe²⁺	Cathodic	-0.076	Mtr EET Complex	-	Initial OD = 0.01	Graphite	EET	Summers et al. [142]
Shewanella oneidensis MR-1	Lactate, Cr5⁺/Cr⁶⁺	Anodic	0.3	Mtr EET Complex	-	Initial OD = 0.3	Graphite	EET	Xafenias et al. [143]
Acetobacterium spp + Rhodobacteraceae	CO₂ to acetate	Cathodic	-0.59	H₂	≈ 0.17	0.5	Graphite	H₂	Marshall et al. [144]
Ralstonia eutropha	CO₂ to isobutanol	Cathodic	-1.4	H₂ and Formate	≈ 1	Initial OD = 0.8-1	Indium foil	H₂ and Formate	Li et al. [43]
Ralstonia eutropha	CO₂ to biomass and PHB	Cathodic	-0.6	H₂	≈ 0.2	Initial OD = 0.2	Co-P alloy	H₂	Liu et al. [45]

^aCathodic electron flow refers to electron flow from cathode to microbial metabolism, whereas anodic flow indicates electron flow from metabolism towards an anode. ^{b and c}The electrode overpotential is estimated by subtracting the estimated applied electrode potential from the assumed electron acceptor potential at pH 7 (Mtr EET Complex, E = -0.1 V vs SHE; H₂, E = -0.42 V vs. SHE; Formate, E = -0.43 V vs. SHE). References [43, 45, 63, 139,140,141,142,143,144] were used to compile this table

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