85Microbial Fuel Cells and Other Bio-Electrochemical Conversion Devices
2.3.3.3 Cathode Performance
The cathode reaction efciency depends on a variety of factors, including the
concentration and species of the oxidant (electron acceptor), catalyst perfor-
mance, electrode structure and operational conditions.
Oxygen, hexacyanoferrate (K
3
[Fe(CN)
6
]) and permanganate (KMnO
4
),
which possess high redox potentials, have been used as electron acceptors at
the cathode. Although hexacyanoferrate and permanganate may produce a
similar or higher cathode potential than oxygen (OCP
cathode
of 0.70 and 1.38 V
vs. ~0.4 V; [73]), oxygen remains as the most commonly used and promis-
ing cathodic oxidant, due to its free and clean nature. In many cases, oxy