Novel Microfluidic Septum to Optimize Energy Recovery in Single-Chamber Microbial Fuel Cells

This study proposes a redesign of asymmetric single-chamber microbial fuel cells (a-SCMFCs) with the goal of optimizing energy production. In the present work, the new approach is based on the introduction of a novel intermediate microfluidic septum (IMS) inside the electrolyte chamber. This IMS was designed as a relatively simple and inexpensive method to optimize both electrolyte flow and species transfer inside the devices. a-SCMFCs, featuring the IMS, are compared to control cells (IMS-less), when operated with sodium acetate as the carbon energy source. Performances of cells are evaluated in terms both of maximum output potential achieved, and energy recovery (Erec) as the ratio between the energy yield and the inner electrolyte volume. The a-SCMFCs with the novel IMS are demonstrated to enhance the energy recovery compared to control cells exhibiting Erec values of (37 +/- 1) J/m3, which is one order of magnitude higher than that achieved by control cells (3.0 +/- 0.3) J/m3. Concerning the maximum output potential, IMS cells achieve (2.8 +/- 0.2) mV, compared to control cells at (0.68 +/- 0.07) mV. Furthermore, by varying the sodium acetate concentration, the Erec and maximum potential output values change accordingly. By monitoring the activity of a-SCMFCs for over one year, the beneficial impact of the IMS on both the initial inoculation phase and the long-term stability of electrical performance are observed. These improvements support the effectiveness of IMS to allow the development of efficient biofilms, likely due to the reduction in oxygen cross-over towards the anode. Electrochemical characterizations confirm that the presence of the IMS impacts the diffusion processes inside the electrolytic chamber, supporting the hypothesis of a beneficial effect on oxygen cross-over.