Date of Award
2007
Degree Type
Thesis
Degree Name
Master of Engineering Science
Program
Chemical and Biochemical Engineering
Supervisor
Dr. D.Karamanev
Abstract
The main aim of the present work was to study the factors influencing the biogenerator operation, and consisted of three basic parts: membrane conductivity study, development of a cathode and a long-term stability testing. The first part was dedicated to study the conductivity of H+-, Fe3+- and mixed H+ZFe3+- forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117, and Selemion HSF under conditions similar to these in the Fe3+∕Fe2+-H2∕H+ fuel cell in the range of current densities 0-90 mAZcm2. It was found that the conductivities of these membranes in 1.09 M H2SO4 solution decrease in the following order: Selemion HSF > Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS > Nafion 112. The Fe3+-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe3+-form into H+-form of these membranes. Unlike the Nafion membranes, the Fe3+-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (over 70 mAZcm2) that is most probably a result of concentration polarization. The second part dealt with study of the effect of graphite felt activation by a thermal oxidation in air on its electrocatalytic activity towards Fe3+ZFe2+ redox electrode reaction. For the first time, the exchange current densities and electron transfer coefficients determined from the Tafel equation were obtained within the wide range of burn-off levels (0-50%). The maximal catalytic activity was revealed at the burn-off of 17.4%. The cathode having this burn-off level expressed more than two-fold enhancement in the galvanic cell performance as compared to that with the non-activated graphite felt, and allowed to obtain current densities up to 670 mA cm-2 at the cathode polarization as low as 150 mV. The correlation between electrocatalytic activity and a surface chemistry of graphite felt was established. The cell performance was found to be the best when the pH at a point of zero charge and the amount of surface quinoid groups per unit area were minimal. Finally, the third part included long-term stability testing of the biogenerator, which showed that it is capable of generating current densities up to 300 mA cm-2 that in turn is way higher than any known biological fuel cell can attain. The bioreactor showed its very good stability for over 10 months of operation.
Recommended Citation
Pupkevich, Victor, "ELECTROCHEMICAL ASPECTS OF THE BIOGENERATOR" (2007). Digitized Theses. 5075.
https://ir.lib.uwo.ca/digitizedtheses/5075