Vapor-fed bio-hybrid fuel cell

Abstract

BackgroundConcentration and purification of ethanol and other biofuels from fermentations are energy-intensive processes, with amplified costs at smaller scales. To circumvent the need for these processes, and to potentially reduce transportation costs as well, we have previously investigated bio-hybrid fuel cells (FCs), in which a fermentation and FC are closely coupled. However, long-term operation requires strictly preventing the fermentation and FC from harming each other. We introduce here the concept of the vapor-fed bio-hybrid FC as a means of continuously extracting power from ongoing fermentations at ambient conditions. By bubbling a carrier gas (N2) through a yeast fermentation and then through a direct ethanol FC, we protect the FC anode from the catalyst poisons in the fermentation (which are non-volatile), and also protect the yeast from harmful FC products (notably acetic acid) and from build-up of ethanol.ResultsSince vapor-fed direct ethanol FCs at ambient conditions have never been systematically characterized (in contrast to vapor-fed direct methanol FCs), we first assess the effects on output power and conversion efficiency of ethanol concentration, vapor flow rate, and FC voltage. The results fit a continuous stirred-tank reactor model. Over a wide range of ethanol partial pressures (2–8 mmHg), power densities are comparable to those for liquid-fed direct ethanol FCs at the same temperature, with power densities >2 mW/cm2 obtained. We then demonstrate the continuous operation of a vapor-fed bio-hybrid FC with fermentation for 5 months, with no indication of performance degradation due to poisoning (of either the FC or the fermentation). It is further shown that the system is stable, recovering quickly from disturbances or from interruptions in maintenance.ConclusionsThe vapor-fed bio-hybrid FC enables extraction of power from dilute bio-ethanol streams without costly concentration and purification steps. The concept should be scalable to both large and small operations and should be generalizable to other biofuels and waste-to-energy systems.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0755-7) contains supplementary material, which is available to authorized users.

Modeling control and transduction of electrochemical gradients in acid-stressed bacteria

“…Lastly, multi-component model extensions are required for eukaryotes such as yeast, which encounter acid-stress in many renewable and industrial bioprocesses. 105 , 106 , 107 , 108 , 109 In this case, multiple cellular components (e.g., vacuole and plasma membrane) must be modeled in tandem, because of the combined effect of vacuolar and plasma membrane ATPases in maintaining cytosolic pH under acid-stress. 109 , 110 For the wide range of extracellular conditions and cellular physiologies, the increasing availability of kinetic and expression data for transport systems will aid in extending the theoretical framework developed herein.…”