EFFECTS OF ELECTROLYTE ON THE CATHODE PERFORMANCE OF MICROBIAL FUEL CELLS AND MICROBIAL ELECTROLYSIS CELLS

Open Access
Author:
Shahidi Pour Savizi, Iman
Graduate Program:
Chemical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 09, 2010
Committee Members:
  • Michael John Janik, Thesis Advisor
Keywords:
  • DFT
  • MFC
  • MEC
  • adsorption
  • electrolyte
Abstract:
Anion adsorption affects electro-catalytic reaction rates by blocking active sites, altering adsorbed species stability, or modifying the electrostatic potential distribution at the interface. Of specific interest are adsorbed anion effects on electrode kinetics at microbial fuel cell and microbial electrolysis cell cathodes, where oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) occur. These cells operate in buffered solutions containing various anions. Experimental electrode kinetics studies and density functional theory (DFT) are applied to investigate the anion adsorption impact on electrode kinetics. Acetate, dihydrogen and hydrogen phosphate effects are considered on platinum cathodes. DFT predicts the coverage of these anions on the surface as a function of electrochemical potential. The computational results show that acetate and dihydrogen phosphate adsorb at the platinum surface at potentials less than the equilibrium potential of the ORR and greater than the equilibrium potential of the HER. The rate of ORR can therefore be affected due to the adsorption of these anions. Hydrogen phosphate has no effect on ORR and HER because it adsorbs on platinum at potentials greater than the equilibrium potential for these two reactions. Linear sweep voltammetry (LSV) is used to evaluate HER and ORR kinetics in the presence of various anions. Experimental results show that the ORR rate was decreased in the presence of acetate and dihydrogen phosphate. The HER rate was increased in the presence of dihydrogen phosphate due to the “weak acid effect” of this anion. The computational results exclude the adsorption and surface reduction of phosphate anions as a possible mechanism for the “weak acid effect.”