Performance of a yeast-mediated biological fuel cell

Abstract

Saccharomyces cerevisiae present in common Baker's yeast was used in a microbial fuel cell in which glucose was the carbon source. Methylene blue was used as the electronophore in the anode compartment, while potassium ferricyanide and methylene blue were tested as electron acceptors in the cathode compartment. Microbes in a mediator-free environment were used as the control. The experiment was performed in both open and closed circuit configurations under different loads ranging from 100 kOmega to 400Omega. The eukaryotic S. cerevisiae-based fuel cell showed improved performance when methylene blue and ferricyanide were used as electron mediators, rendering a maximum power generation of 146.71+/-7.7 mW/m(3). The fuel cell generated a maximum open circuit voltage of 383.6+/-1.5 mV and recorded a maximum efficiency of 28+/-1.8 % under 100 kOmega of external load.

Keywords: Fuel cell; bio-catalyst; mediators; yeast.

Figure 1.

The yeast fuel cell with its constituent redox cycles in the anode and the cathode compartment. Note: MB_ox – Methylene Blue (oxidized); MB_RED-Methylene Blue (reduced)

Figure 2.

Anaerobic fermentation pathway of Saccharomyces cerevisiae - under anaerobic conditions, yeast will transform pyruvate to ethanol. The reduction of NAD+ to NADH will generate two ATP molecules, two H+ ions and two electrons [15].

Figure 3.

The cyclic voltammogram for 50 mM methylene blue solution with carbon electrode. Scan rate 0.05 V/s, potential range –0.1 V– 0.4 V. Reduction and oxidation peaks at 0.13 V and 0.18 V respectively.

Figure 4.

The cyclic voltammogram for 50 mM potassium ferricyanide solution with carbon electrode. Scan rate 0.05 V/s and the potential range –0.2 V to 0.6 V. Reduction and oxidation peaks at 0.13 V and 0.20 V respectively.

Figure 5.

(A) Measured values of the cell open circuit voltage between anode and the cathode; (B) The potential variation in the anode; (C) The potential variation in the cathode. Cathode and anode potentials were measured against Ag/AgCl electrodes and subsequently converted to NHE by adding 0.197V; EX1 to EX6 are the samples prepared as given in Table (2); (ac- anode chamber, cc- cathode chamber); MB-methylene blue; PF - K₃Fe(CN)6.

Figure 6.

Variation of fuel cell parameters under different load conditions (i.) Power Vs Load, (ii) Load current Vs Load and (iii) Load voltage Vs Load.

Figure 7.

A model diagram for a fuel cell with R_i the internal impedance, ξ the OCV of the cell, and R_e the external load (V_e and V_i are the voltage drops across R_e and R_i).

Figure 8.

The fuel cell internal impedance variation under different loads

Figure 9.

The efficiency variation of the fuel cell under varying external loads.