Chemical pre-treatment of commercial carbon felt used as anode of Microbial Fuel Cells

Microbial Fuel Cell (MFC) is a promising technology to convert biodegradable materials present in wastewater into electricity, under anaerobic conditions. The potential application in the near future is likely to be a sustainable process for waste water treatment, stand-alone sensors for long-term operations in low accessibility regions, mobile robot/sensor platforms and renewable energy systems. Conductive materials inside anode and cathode chambers of MFC, assume a fundamental key point for the overall MFC performance. Electrode materials vary in their physical and chemical properties, thus, they also vary in their impact on microbial selection attachment, electron transfer, electrode resistance and the rate of electrode surface reaction. Therefore, in order to promote electrons transfer, the electrode materials should have the following properties: good electrical conductivity, strong biocompatibility, chemical stability and high anti-corrosion, large surface area and adequate mechanical force. In this way, to render MFCs into a cost-effective and energy sustainable technology, efforts have been done to increase power generation. In this respect, focus on low cost commercial materials and up-grade of electrode surface characteristics, in terms of electrical conductivity and morphology structure represent a high challenging task. For this reason, in this work commercial carbon felt has been used as anode electrode after satisfactory pre-treatments. Acid treatment by HNO3 soaking and polyaniline deposition have been made on carbon felt before to test in MFC. Tests have been conducted by a two-compartment laboratory prototype of MFC under the same operation conditions using Saccaromyces cerevisiae as active microorganisms, varying only the anode electrode: 1) Carbon felt, 2) Carbon felt previously treated by HNO3 and 3) Carbon felt with PANI depositions. Electrochemical experiments were carried out to determine how the nitric acid and PANI depositions affected the performance of carbon felt material. Results obtained using Linear Sweep Voltammetry technique shows an increase of performance in terms of power density for both pre-treatment processes. Commercial carbon felt material showed a power density of 12 mW L-1, while carbon felt treated by HNO3 and PANI depositions showed a power density of 32 mW L-1 and 35 mW L-1, respectively. The increase of the performance of carbon felt material by HNO3 soaking, can be related to an increases of the surface roughness which favour the adhesion of microorganisms, while taking into account the electro-catalytic properties of polyaniline surface, improvement of current generation seems be due to the increase of the carbon source oxidation. Electrical characterizations, in terms of resistivity evaluated directly on electrode materials show that both pre-treatments induce to a strong reduction of resistivity referred to carbon felt without pretreatment.