An Investigation on the Effect of Neutral Red Concentration on Voltage and Current Outputs for Microbial Fuel Cells

A major contributor to environmental pollution is the increasing quantity of sewage produced by growing human population centers. To address the need for alternative waste-management solutions, we report here the use of a yeast microbial fuel cell to break down complex carbohydrates found in sewage and convert them into electricity. The study utilized a microbial fuel cell set with two 250 mL glass half cells. The anode cell contained sucrose, neutral red, and the yeast species Saccharomyces cerevisiae. The cathode cell contained sodium potassium phosphate buffer. The yeast culture was made using 5 g of Fleischmannâ??s yeast extract grown in one liter of deionized water supplemented with 20 g of sucrose. This yeast culture was continuously mixed for one week before usage. The working and counter electrodes were made of a carbon fiber cloth weave with a surface area of 50 cm² and placed in the cathode cell. The anode cell contained a silver/silver chloride reference electrode. The membrane used between the cells was Nafion 212, soaked in deionized water before runs. The anode cell was sparged with nitrogen to remove oxygen from the chamber and under these anaerobic conditions, yeast will readily undergo respiration to produce electrons which can be harvested in the microbial fuel cell. This is accomplished by the neutral red, which acts as an electron mediator transferring high energy electrons from the yeast to the anode electrode.

Three electrochemical cell characteristics were measured using a potentiostat: voltage, anode potential, and amperage. The neutral red concentrations tested were 1, 3, and 5 mM based on previously reported values in literature. From the collected data, the 1 mM neutral red run was able to generate the highest peak cell voltage of 0.25 V but all three runs leveled out at approximately 0.2 V after 72 hours. The anode potential for each concentration run was 9 V, with minimal difference between runs. The 1 mM run generated 50 pA, approximately 5 times as much as the 3 mM run. The cell voltage is consistent with previous literature, generally placing cell voltage between 0.2 and 0.4 V for neutral red yeast fuel cells, while the current data is lower than previously reported values. Based on our data, it appears that increased electron mediator concentrations has a negative effect on cellular respiration in yeast cells, leading to reduced overall cell voltage and current generation.