Can biofuel cells be a sustainable energy conversion device?

Betina Tabah, Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Indra Neel Pulidindi, Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Aharon Gedanken, Chemistry, Bar-Ilan University, Ramat-Gan, Israel

Need for alternative energy sources is exponentially increasing, especially in the transportation sector. Fuel cells are green energy conversion devices much sought after even in the aviation sector. Use of biofuels in fuel cells for transportation is an attractive idea from energy and environmental perspectives. Bioethanol is a promising substitute to conventional gasoline owing to its energy density value (24 MJ/L) which is close to that of gasoline (34.3 MJ/L). Moreover, bioethanol could be produced from renewable sources such as plant materials and waste papers, which are abundant. In principle, the bioethanol production from renewable materials should be energy efficient meaning the net energy output should be higher than that of the net energy input. Successful utilization of solar energy for bioethanol production from biomass (containing starch or cellulose-based polysaccharides) will alleviate the fuel shortage problem to some extent. The current research is focused on using solar energy for the conversion of starch to ethanol (by fermentation) in a single step. 5 wt. % aqueous starch solution was fed into the reactor bed charged with yeast and amylase and interesting results on bioethanol production were obtained. About 2.5 wt. % ethanol (~30 mL/day) was collected daily. The fermentation was monitored for two months and at the end, 38 g ethanol was obtained which corresponds to 84 % of the theoretical yield. The ethanol produced from starch using a solar fermentor is being investigated for its potential to operate direct ethanol fuel cells. In contrast to conventional fermentation, no glycerol but its reduced product 1,3 propanediol was observed in the fermentation broth. Ethanol production with no energy input signifies the importance of this new process. Future studies will be devoted on the possibility of direct conversion of cellulose to ethanol and its subsequent use in biofuel cells.