Many efforts were made to seek alternative renewable energy sources to replace fossil fuels due to their depletion. The microbial fuel cell (MFC) uses microorganisms that are widely available in nature to generate electricity; therefore, it is one of the renewable and environmentally friendly energy sources.
In this study, we used native mixed-culture microorganism of Taiwan for macro- and micro-scale MFC investigations. In the two-chambered macroscale MFCs, combinations of different electrodes, electrolytes and external loads were used to study their impacts on the power generation. Macroscale MFCs using free floating carbon paper as electrodes produced the greatest power output of 1.03×10-2 W/m2 among those using carbon cloth (6.40×10-3 W/m2), combination of titanium and carbon paper (3.3×10-4 W/m2), combination of titanium and carbon cloth (5.20×10-5 W/m2) and combination of carbon and platinum (3.12×10-6 W/m2). Using ferricyanide in the cathode resulted in a maximum power output of 3.3×10-4 W/m2, while using phosphate buffer and algae generated
3.54×10-4 W/m2 and 1.40×10-7 W/m2, respectively. When the experiments were conducted with different external loads, the maximum power output of 2.814×10-2 W/m2 was obtained using the 500 ohms external load. The estimated internal resistances of these devices were in the range from 500 to 10k Ω.
For the membraneless microfluidic MFCs (µMFCS) with a Y-channel and gold microelectrodes, experiments were conducted using various flow rates and the maximum power was achieved when the flow rate was 10 ml/hr. The relative power output between different flow rates were 100% (10 ml / hr), 6.22% (4 ml / hr), 8.10% (7 ml / hr), 81.22% (50 ml / hr), 43.16% (90 ml / hr), 12.10% (150 ml / hr), and 5.38% (200 ml / hr). The µMFCS generated great power density with a value of 21.42 W/m2, which was 2000 folds higher than that from our macroscale MFCs with optimized conditions (0.01 W/m2). These devices had internal resistance around 10kΩ.
In conclusion, the native mixed-culture microorganism showed great potential in generating electricity with optimized configurations and experiment conditions. The membraneless µMFCS offered alternative choices for building MFCs and had abilities in producing much higher power density than their macroscale counterparts.

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