Low-cost thermistor electrodes for numbering-up thermodynamic studies on electroactive biofilms

First bioelectrocalorimetric investigations of Geobacter enrichment biofilms performing extracellular electron transfer (EET) revealed the microbial electrochemical Peltier heat ( Π m ) as an entropic barrier leading to energy losses. Like its abiotic analog, Π m can be assumed to be a material constant, depending on the redox species performing EET, the working electrode material, and the electrolyte composition. To foster bioelectrocalorimetric research, a thermistor electrode setup was developed for determining Π m . Thermistor electrodes can be easily numbered up and hence allow systematic thermodynamic studies of the consequences of Π m on the energy balances of electroactive microorganisms and microbial electrochemical technologies. Thermistor electrodes were calibrated by applying defined heat pulses, resulting in a heat transfer coefficient K (0.595 ± 0.303 W K −1 ) and a heat capacity m C p (78.057 ± 28.705 J K −1 ). Subsequently, Π m of Geobacter enrichment biofilms cultivated on gold thermistor electrodes was measured, and the obtained Π m = 16.6 kJ e-mol −1 is comparable to values determined using an established bioelectrocalorimetric setup. This proof-of-concept lays the foundation for optimizing thermistor electrodes to systematically investigate and engineer the energy fluxes at the interface of electroactive microorganisms and electrodes. • Low-cost Thermistor electrodes allow systematic studies on the microbial electrochemical Peltier heat Π m . • Thermistor electrodes were calibrated with defined heat pulses. • Π m amounted to 16.6 kJ mol −1 for Geobacter enrichment biofilms at gold electrodes. • Obtained Π m is comparable to bioelectrocalorimetric studies. • Reactor optimization is required to improve signal stability and sensitivity.