Spinel Oxide Catalysts for Oxygen Reduction in Microbial Fuel Cells

Microbial fuel cells offer many advantages in the production of energy from renewal sources.  Unfortunately, their commercial implementation has been hampered by some serious technical challenges.  In particular, like most fuel cells that incorporate oxygen reduction, power output is limited by the large overpotential for this reaction.  Incorporation of a Pt catalyst will enhance the reaction rate to acceptable levels but at an unacceptable cost and, while less expensive alternative catalysts have been considered, none have shown the catalytic activity of Pt.   This poster reports results of our efforts to develop a catalyst based on a mixed-transition metal oxide with spinel composition, Ni_xCo_3-xO₄ (where x is approximately 1), that was previously found to be promising for oxygen reduction under alkaline conditions but not, to the best of our knowledge, the pH-neutral environment of a microbial fuel cell.  The oxide is also known to exhibit an electron conduction mechanism based on small polaron hopping as well as a tendency to surface “reorganize” in response to its chemical environment, both possible advantages to interfacial reactions involving dissolved oxygen.  Cyclic voltammograms of electrodes impregnated with Ni_xCo_3-xO₄ showed marked improvement in oxygen reduction rates in neutral-pH-buffered solutions over uncatalyzed electrodes.  The poster also reports on recent results of using electrodes modified with Ni_xCo_3-xO₄ in a bench-scale microbial fuel cell.