The bacterial battery and the effect of different exposure conditions on biofilm properties

A galvanic cell with pure copper and Al 2024 and Shewanella oneidensis MR-1 in Luria Bertani (LB) medium and a control cell, which did not contain the bacteria, have been tested. Potentiodynamic polarization experiments were used to determine cell voltage ( V)–current ( i) and power ( P)– i curves as a function of time. The results for the cell without bacteria demonstrated that the maximum power output was obtained in the first day and dropped drastically in the following days. For the cell with MR-1 the power output of the cell increased slowly with time for around 100 days and remained at similar values for another 100 days. For pure Cu significant changes of the impedance spectra were found in the presence of MR-1. The impedance spectra resembled those usually observed for polymer-coated metals. In order to investigate this phenomenon in more detail, the effects of the different exposure conditions on the electrochemical behavior of copper were evaluated in LB containing MR-1. A second time constant was observed in the impedance spectra of copper that was partially immersed in the test solution (cell B). Complete immersion of copper in the electrolyte (no air/liquid interface) or deaeration of cell B resulted in one-time-constant spectra that are typical of those found for passive metals. Excellent corrosion protection was provided by MR-1 regardless of exposure condition. The corrosion potential increased with time for the Cu electrode exposed in cell B, while it decreased for the other two exposure conditions.