Metal Organic Frameworks Electrodes for Microbial Fuel Cell Applications and Hydrogen Production

Abstract

Microbial Fuel Cell is an innovative technology that offers production of clean electricity while treating the wastewater. One of the most important challenges affecting power generation is the overpotential losses at the cathode due to lower reaction rates occurring on the active sites of the electrode. This overpotential causes a voltage drop due to limitation of electrons transfer to the electrodes. Oxygen reduction reaction (ORR) is considered an important factor affecting the overall performance. Increasing the surface area of the electrode and using more effective catalyst can be considered as two of the most effective methods to overcome these problems. In this thesis, a novel in situ-growth of a 2D shell nanowires of ZIF-67 as template for N-doped carbon (Co/NC) via carbonization route was developed to enhance the ORR performance. The effects of different reaction time, different annealing temperature along with the effect of sulphur and selenium doping were studied for better oxygen reduction reaction (ORR) activity. The growth of the metal-organic framework (MOF) template on the carbon cloth was confirmed using SEM, XRD, and FTIR. The CoS/NC exhibited an enhancement on the ORR activity as evidenced by an onset potential and half wave potential of 0.0 vs VAg/AgCl and -0.1 vs VAg/AgC, respectively, with a limited current density exceeding the commercial Pt/C. Operating CoS/NC on MFC revealed a maximum power density of 30 ± 2.5 mW/m² , a maximum current density of 180 ± 2.5 mA/m² and a constant current discharge of 28 ± 2.5 mA/m²; such values are comparable to the commercial Pt/C. The enhancement of the ORR activity was mainly due to the 2D shell nano wire structure, conductivity of the ZIF-67 and the sulphur doping. Optimization study using real wastewater provided form Al Aweer treatment plant was conducted for the purpose of enhancing hydrogen production. The maximum power and current densities were 250 ± 2.5 mW/m² and 1100 ± 2.5 mA/ m², respectively, using a ratio 45:55% of anaerobic sludge to 3 g acetate buffer solution. A maximum biohydrogen of 0.5 ml/d was achieved using microbial electrolysis cell at an applied voltage of 1.4 V.