Abstract
Rice paddy-field microbial fuel cells (RPF-MFCs) are devices that exploit rhizosphere bacteria to generate electricity from soil organic matter, including those excreted from roots. Previous studies have examined factors affecting electric outputs from RPF-MFCs and demonstrated that RPFMFC was able to generate electricity up to 80 mW·m-2 (based on the projected area of anode). The present study operated RPF-MFCs with different sizes of anodes and cathodes and examined how electrode sizes affected electricity generation. We show that anodes are the limiting factor for electricity generation immediately after commencing the operation, while cathodes become the limiting factor after anode performances are sufficiently increased. RPF-MFC achieved the maximum power density of 140 mW·m-2 (based on the projected area of anode), when the cathode is sufficiently larger than the anode. Results suggest that the cathode needs to be improved for eliciting the maximum capacity of rhizosphere bacteria for electricity generation in RPF-MFC.
Highlights
Rice paddy-field microbial fuel cells (RPF-MFCs, Figure 1) are sediment-type MFCs that convert soil organic matter into electricity with the aid of rhizosphere microbes [1] [2]
RPF-MFCs utilize organic matter excreted from rice roots for electricity generation
Another study combined phylogenetic and metagenomic approaches for characterizing anode-associated microbes, suggesting that bacteria affiliated with the genus Geobacter were involved in electricity generation in RPF-MFCs [6]
Summary
Rice paddy-field microbial fuel cells (RPF-MFCs, Figure 1) are sediment-type MFCs that convert soil organic matter into electricity with the aid of rhizosphere microbes [1] [2]. Another study combined phylogenetic and metagenomic approaches for characterizing anode-associated microbes, suggesting that bacteria affiliated with the genus Geobacter ( those closely related to G. pelophilus and G. psychrophilus) were involved in electricity generation in RPF-MFCs [6]. Another previous study has examined factors affecting electricity generation in RPF-MFCs and found that cathode modification with platinum catalysts, anode position and external load largely affected power outputs [7]. Compared to the maximum power density (6 mW∙m−2) reported in the first trial of RPF-MFCs in 2008 [5], the latest power density (80 mW∙m−2) has increased over 10-fold, showing that the RPF-MFC technology has progressed substantially
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