Abstract
Plant-microbial fuel cells (PMFCs) are a class of renewable biomass energy that relies on the rhizodeposition of plants to generate power. In this study, the optimization of electrode spacing, number, and combinations were studied to maximize the power output of a soil PMFC growing Cynodon dactylon. To achieve this, compartmentalization tests were carried out as well as polarization. The anode-cathode distance was found to produce the highest voltage at 3 inches apart, wherein a smaller gap resulted to lower power, and a slight increase in the gap did not result to a loss of power. The use of multiple electrodes was also examined, and the results have shown that maximum power was obtained at inter-electrode distance of 18 cm. Smaller gaps registered lower voltages, and larger gaps gave a sudden drop in voltage. The effect of limiting one electrode was also observed. In anode-limiting conditions, it was found that both power and power density were maximum when there are 4 cathodes corresponding to one anode. When the reverse was done, it was shown that both power and power density continuously dropped if there are multiple anodes corresponding to one cathode only. This led to the conclusion that cathode design is more crucial in PMFCs as it utilizes the rate-limiting step. The tests of using multiple paired electrodes to determine the power-power density relationship results to a contradiction of behaviour in MFCs, wherein both power and power density increases as the electrode surface area is increased. These results are important building blocks to the goal of utilizing PMFCs in the future in larger scales with appreciable power generation.
Highlights
Plant-microbial fuel cells (PMFCs) are bioelectrochemical systems (BES) that utilize the plant and microbe relationship in the rhizosphere region to produce bioelectricity [1]
This study has demonstrated the possibility of scale-up using multiple electrodes in a PMFC
Guided by the result that PMFCs are limited by cathode surface area, more efficient and larger PMFCs can be made
Summary
PMFCs are bioelectrochemical systems (BES) that utilize the plant and microbe relationship in the rhizosphere region to produce bioelectricity [1]. Achieving power densities of MFCs high enough to make it economically viable is challenging due to the various internal resistances to consider such as ohmic, activation, bacterial metabolic and concentration losses [3]. A possible solution is stacking of smaller cells which maintains lower resistances [4]. Ohmic losses are brought about by the resistance of the electrons and protons to flow through the electrodes and membrane, respectively. This can be lessened by reducing the distance between electrodes or by removing the membrane [6]. Concentration losses are brought about when mass transfer of chemical species such as protons and oxidants are limited. Limiting the available electrons readily to react with the proton and hydrogen in the cathodic region
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