Urine has been demonstrated to
be an effective feed stock for MFC operation with the additional
benefit of nitrogen, phosphate and potassium recovery from the
fuel [8]. In particular, according to Ieropoulos et al [9]. urea is
enzymatically hydrolysed to ammonia and carbon dioxide.
Ammonia is then oxidised at the anode of the MFC to generate
mainly nitrite and in smaller amounts nitrate [10].
Despite the breadth of applications and the growing interest in
MFC technology over the past two decades, commercialisation of
MFCs for energy generation has not yet been realised.
The major limiting factors that hinder the practical implementation
of MFCs at large scale, are the cost of materials used and the
difficulties in the scale-up process [11].
Typically the electrodes are made from highly cost-effective
materials such as carbon cloth, carbon paper, and graphite * based
rods, plates and granules. Recently, even some metals, such as
copper and silver, have been shown to be effective anode materials
[12]. However, expensive metals, such as platinum, are usually
used at the cathode to enhance the oxygen reduction reaction
(ORR) [13–15]. Recently, the use of biomass-derived catalysts
recovered from waste has been proposed as an effective alternative
to expensive metal ORR catalysts. In particular, biomass-derived
materials from wood [16], sewage sludge [17] and bananas [18]
have been shown to function as ORR catalysts to boost MFC
performance whilst reducing the device cost and its carbon
footprint. Doping these materials with heteroatoms such as
nitrogen and sulphur [19], also in combination with nanoparticles
like iron [20], has been shown to enhance the catalytic activity
towards the ORR even further.