Pyrogenic carbon is now known to be able to transfer electrons between microbes and extracellular acceptors. Surface quinone groups have currently been identified as the likely pathway for pyrogenic carbon mediated electron transfer. Yet, pyrogenic carbon is conductive, and the direct extracellular electron transfer (DEET) pathway through the carbon matrices has not been fully understood. Such properties can allow electrons to travel distances to reach different redox environments, what we dub in this paper the ‘Biosnorkel Mechanism’. We have examined the kinetics of electron transfer through environmentally relevant pyrogenic carbon matrices separately from the charging and discharging behavior of surface functional groups using multiple voltammetric techniques, and applied the kinetic behavior to characterize the DEET processes between microbes and pyrogenic carbon.<br/>To complete this work black walnut wood feedstock was pyrolysed from 400 to 800°C and electrochemical, bioelectrochemical tests, and physicochemical tests were performed. <i>Geobacter sulfurreducens</i> strain PCA was used for bioelectrochemical tests exploring electron transfer mechanisms to the pyrogenic carbon with a focus on current generated during the exponential growth phase. Current production confirmed DEET processes were present. Analyzing electron transfer rate constants resulted in an “S”-shaped trend, indicating three zones of pyrogenic carbon behavior based on their pyrolysis temperature (Figure 1): a bacterial growth-limiting temperature range at 700-800°C, a mixed limiting range at 600-700°C, and pyrogenic carbon electron transfer-limiting range below 600°C. Ongoing work is focused on quantifying how active DEET, material capacitance, and surface functional groups are for overall electron transfer, and the role of pyrogenic carbon in natural environments and for engineered conservation efforts.

Biosnorkel mechanism–direct extracellular electron transfer by pyrogenic carbon

253rd National Meeting (2017)

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