International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 06 | June -2017
p-ISSN: 2395-0072
www.irjet.net
Designing the Shape of Graphite Anode for Microbial Fuel Cells to Increase its Efficiency Sushma S1, Dr. Harish Anand K S2 1 PG
Student, Department of Mechanical Engineering, School of Engineering & Technology, Jain University of Mechanical Engineering, Department of Mechanical Engineering, School of Engineering & Technology, Jain University ---------------------------------------------------------------------***--------------------------------------------------------------------2HOD
Abstract - Microbial fuel cell (MFC) technology has the
Reactions of MFC:
potential to become a renewable energy resource by degrading organic pollutants in the wastewater. The performance of MFC depends on kinetics of electrode reactions within the cell. The design of the electrode has a major role in improving the working of the microbial fuel cells. The electrode is designed in such a way that it increases the surface area of the electrode as well as decreases the amount of materials used for the electrode hence reducing the cost of operation and making it a cheaper method than the previous models.
At Anode:
Key Words: Microbial fuel cells, Anode, Cathode, Graphite
1. INTRODUCTION A microbial fuel cell (MFC), or biological fuel cell, is a bioelectrochemical cell that drives an electric current. This current is derived by utilizing bacteria. MFCs can be differentiated into two categories: mediated and unmediated. The first MFCs were developed in the early 20th century which is used as mediator. Unmediated MFCs developed in the year 1970s. In this MFC the bacteria have cytochromes on their outer membrane which are electrochemically active redox proteins and can transfer electrons directly to the anode. In the 21st century MFCs used commercially for wastewater treatment. A microbial fuel cell (MFC) is a device that converts chemical energy into electrical energy by the microbial action. These cells are constructed using bioanode and/or a bio-cathode. A membrane is present in most of the MFCs that separates the compartments of the anode (where oxidation takes place) and the cathode (where reduction takes place). The electrons produced in MFC during oxidation are transferred directly to a redox mediator species. The electron flux is moved to cathode and the charge balance of the cell is compensated by ionic movement inside the cell, usually across an ionic membrane. Most MFCs uses an organic electron donor that is oxidised to produce CO2, protons and electrons. In the cathode reaction, it uses various electron acceptors that influence the reduction of oxygen. However, other electron acceptors, including metal recovery by reduction, water to hydrogen, nitrate reduction and sulphate reduction.
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C12H22O11 + 13H2O → 12CO2 + 48H+ + 48e− At Cathode: 4H+ + O2 + 4e- → 2H2O
2. WASTEWATER TREATMENT MFCs are used in waste water treatment to generate energy utilizing anaerobic digestion. This process will also reduce pathogens. However, it requires temperature of above 300C and requires an extra process to convert biogas into electricity. Spiral spacers are used to increase electricity generation by forming helical flow in MFC.
3. ELECTRODE MATERIAL AND DESIGN The selection of suitable electrode material is a crucial for the performance of MFCs in terms of bacterial adhesion, electron transfer and electrochemical efficiency. There are methods to increase the power production using various carbon-based materials such as carbon paper, carbon felt, carbon fiber as well as carbon nanotube-based composites. To apply the MFC technology in practice, the material cost should be reduced and should maximize the power densities. The cathode materials should have catalytic properties for oxygen reduction. Although the criteria’s to select materials in MFC for the anode and cathode are different, in general both anode and cathode should possess the following properties: •
Surface area and porosity:
The output power of MFCs is influenced by the surface area of electrodes. The Ohmic losses are directly proportional to the resistance of electrode. The easiest way to reduce the resistance is to increase the surface area by keeping the volume same, and thus increases the efficiency of MFC. Further, a high surface area provides more sites for reactions and enhancing electrode kinetics in MFC. However, porosity will decrease the electrical conductivity of the material.
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