Coupling biofuels with fuel cells (FCs) can reduce the cost of purification and transport of ethanol and other biofuels, especially at smaller scales. However, long-term operation requires strictly preventing the fermentation and FC from harming each other. Here we discuss various approaches to closely coupling fuel cells and fermentations (creating a ‘biohybrid’ fuel cell) with a particular focus on extracting ethanol from yeast fermentation with a carrier gas (N2). This protects the FC anode from the catalyst poisons in the fermentation (which are non-volatile), and also protects the yeast from harmful FC products (notably acetic acid) and from build-up of ethanol. Reducing the build-up of ethanol is particularly beneficial when using non-yeast based fermentations or operating yeast in consortia with other organisms to break down a wider range of substrates. Since vapor-fed direct ethanol FCs at ambient conditions have never been systematically characterized (in contrast to vapor-fed direct methanol FCs), we first show that 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 greater than 2 mW/cm2 obtained. We then demonstrate the continuous operation of a vapor-fed bio-hybrid FC with a yeast fermentation for five months, with no performance degradation due to poisoning of either the FC or the fermentation.

Biohybrid fuel cells for power generation directly from fermentations

254th National Meeting (2017)

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