Microstructured electrodes for microbial energy conversion: from organic matter to electrical current

MARIANO PRUDENTE; DIEGO MASSAZZA; JUAN PABLO BUSALMEN; HERNÁN ROMEO

Paraná (Entre Ríos)

Congreso; IV Congreso de Microfluídica Argentina; 2017

Facultad de Ingeniería de la Universidad Nacional de Entre Ríos

Microbial fuel cells (MFCs) come up as a new and appealing possibility for both the treatment of organic waste and the generation of electrical current. MFCs are similar to conventional fuel cells but take advantage of electro-active microorganisms, especially those from the genus Geobacter, which act by converting the energy stored in chemical bonds of organic compounds into electricity. In recent years, this concept has triggered considerable interest among academic researchers towards environmentally safe and novel low cost biotechnologies. A MFC consists of an external electrical circuit, which links anodic and cathodic compartments separated by a proton or cation exchange membrane. Generally, the anodes used consist of non-porous graphite rods immersed in the bacterial culture medium, upon which the colony of cells can develop. Recent reports have indicated that long-term development of anodic bacterial biofilms does not correlate with current production, mainly due to a drop in voltage through the biological matrix as the distance to the electrode surface increases. This imperfect conduction leads to a significant loss in the electrical production. For this reason, trial-applications that make use of electro-active biofilms are not yet feasible. However, this situation may change if the electric connection between cells in the biofilm and the electrode is improved.This work aimed at developing electrically conducting ceramic supports (Ti4O7) exhibiting structured microporosity features. Specifically, electrode pores consisted of microchannels longitudinally aligned along the electrode architecture, to allow the proliferation and development of electro-active microorganisms inside the porous structure, increasing at the same time the contact area between cells and the conducting material. By building a range of pore sizes (from 10 to 100 µm), we demonstrate that this parameter critically influences the amount of bacteria per electrode unit volume, emerging indeed as the cornerstone to modulate the bio-anode volumetric current density. However, the obtained trend evidenced that the surface area is not directly paired to the bio-electrode efficiency at high surface-to-volume ratios, driving the attention to the fluid dynamic behavior inside the pores. According to our results, it is possible to modulate the anodic volumetric current density up to one of the highest levels ever reported in the area of MFCs (over 20 kA.m-3). These findings knock down the current paradigm towards increasingly higher bio-anode surface areas and provide new perspectives for designing future scaffolds, by considering hydrodynamic constraints inside the electrode microchannels for the optimal anode performance.