Abstract
Plant-Microbial Fuel Cell (PMFC) technology is a promising bioelectrochemical system that can exploit natural plant rhizodeposition to generate electricity. PMFCs can be used to simultaneously generate electricity while growing edible plants, as illustrated in this study. However, the common problem encountered for soil PMFCs is the low power output. To solve this problem, the stacking behavior of PMFCs was examined to maximize the power output of several cells. A grid of 9 PMFCs (3x3) was constructed with stainless steel and carbon fiber electrodes growing green beans (V. ungiculata spp. sesquipedalis) for stacking purposes. Stacking results have shown that too many cells connected in series will result in voltage losses, while stacking in parallel conserves voltage between cells. Stacking a maximum of 3 cells in series is acceptable based on the results, since cumulative stacking revealed that voltage reversals can reduce the overall potential of the stack if there are too many connected cells. Stack combinations were also tested, resulting in an enhanced performance upon combining series and parallel connections allowing power to be amplified and power density to be conserved. The combination of three sets of three cells in series stacked in parallel (3S-P) generated the highest power and power density (160.86 μW/m2) amongst all combinations, showing that power amplification without losses to power density are possible in PMFC stacking. Overall, proper stacking combinations have been shown to greatly affect the performance of PMFCs. It is hoped that the results of this study will contribute to the efforts of applying PMFC technology on a larger scale.
Highlights
An increasing pressure to reduce our carbon emissions from the energy sector to curb excessive global warming points to the development of renewable energy technologies
A steady increase in voltage was observed during the vegetative stage as more rhizodeposits are exuded in the roots, the voltage of Plant-Microbial Fuel Cell (PMFC) started to decrease at the onset of flowering, and further decreased during fruit development
This suggests an increase of nutrition priority to the fruits of the plant decreases the rhizodeposits available for microorganisms in the rhizosphere, leading to lower bioelectrical output. This is another hurdle for PMFCs growing food plants as most of them are valued for their fruits
Summary
An increasing pressure to reduce our carbon emissions from the energy sector to curb excessive global warming points to the development of renewable energy technologies. One subclass of BESs are Plant-Microbial Fuel Cells (PMFCs) They serve the same functions as solar photovoltaic cells; PMFCs generate electricity from sunlight that drives photosynthesis, forming carbon compounds. Some of these compounds are stored by the plant while some are excreted through the roots through a process called rhizodeposition (Nitisoravut & Regmi, 2017; Bais et al 2006). Some bacteria, called exoelectrogenic bacteria, are capable of releasing protons and electrons from their cells through extracellular electron transfer (Ishii et al, 2017) Through this process, PMFCs generate electricity by utilizing sunlight to fix atmospheric carbon to its roots, which in turn is oxidized by rhizospheric bacteria. PMFCs are attractive to use in agricultural lands as it permits the simultaneous generation of electricity and biomass production
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