Stacking of aquatic plant-microbial fuel cells growing water spinach (Ipomoea aquatica) and water lettuce (Pistia stratiotes)

Abstract

Plant-microbial fuel cells (PMFCs) are a sub-branch of a class of promising bioelectrochemical systems which are capable of simultaneously supplying biomass and renewable energy from photosynthesis and root exudation. In this study, the possibility of power amplification through stacking was tested. Ipomoea aquatica and Pistia stratiotes were used as model plants in this study because their biomass is valued as food for humans and livestock, respectively. In a brief 7-day experiment, maximum power densities of 6.35 mW / m2 for I. aquatica and 3.54 mW/m2 for P. stratiotes were obtained from aquatic PMFC assemblies. No significant difference in voltage was observed between the two plants, although the current and power output of I. aquatica were significantly higher than that of P. stratiotes. Connecting three cells in series resulted to three times higher voltage but the same current, and connecting three cells in parallel resulted to three times higher current but the same voltage for both plants. Power was also amplified by stacking. There is no significant difference in the power produced by the cells connected in series or parallel. Power density remained constant due to the increase in surface area of electrodes used upon stacking. These results are consistent with the rules of electric circuits and would become a valuable tool in the computational design of larger systems with numerous cells that can supply a large part of our electricity demands. For future studies, assemblies with more cells are recommended to establish the upper limit of the validity of the series/parallel models and can be tested with other plants.