Microbial Fuel Cells in Power Generation and Extended Applications - Biotechnology in China: Biofuels and Bioenergy - page 171

a mini-MFC with a volume of only 1.2 mL, which produced a high current density
of 44 mA/m 2 (normalized to anode area). A high power density of 15 W/m 3 was
also obtained in a dual-chamber microfluidic MFC, which contained a vertically
stacked 1.5 lL anode chamber and 4 lL cathode chamber [ 27 ]. This high
power output suggests a high possibility of powering nano-devices using on-chip
bioenergy. Despite their good performances in power generation, such MFCs
generally suffer from brittleness and a time-consuming and expensive fabrication
process. Recently, Chen et al. [ 28 ] successfully fabricated a single-chamber
mini-MFC array using a microfabrication technique. The MFC array contains eight
anodic chambers, each with a uniform volume of 25 lL. Gold was chosen as the
anode material because of its high conductivity and compatibility with conven-
tional microfabrication methods. This mini-MFC exhibited excellent power
generation performances compared with other microliter-scale MFCs. The current
and power densities reached 29 mW/m 2 and 2148 mA/m 2 (normalized to anode
area), respectively. Moreover, the fabrication process is relatively simple, and the
MFC components can be readily assembled/disassembled, cleaned and reused.
2.2 Electrodes
To develop practical MFC technologies, one of the biggest challenges is to find
low-cost, highly efficient, and sustainable electrode materials. Indeed, selection of
the proper electrode is of critical importance for MFCs, as the properties of the
electrode can affect bacteria adhesion, electron transfer and electrochemical
reaction efficiency, and the cost of electrode material constitutes a large proportion
of the MFC cost [ 29 ]. Although carbon-based materials, such as carbon paper,
carbon felt, graphite pad, graphite granule, and graphite fiber, have been com-
monly employed for both anode and cathode, a variety of low-cost electrode
materials and modified materials with favorable properties for anode or cathode
reactions are currently under rapid development.
2.2.1 Anodes
Carbon-Based Materials
Anodic electrodes should have a large surface area, good biocompatibility and
high chemical stability. In addition, as electrodes, they should ideally also possess
high electrical conductivity [ 30 ]. Carbon- or graphite-based materials are currently
most widely used [ 29 ]. Their major advantages lie in their excellent surface
properties such as high specific surface area and porosity, and their low cost.
You et al. [ 9 ] built a tube-type air-cathode MFC that used graphite granules as the
anode and a graphite rod as the electron collector, achieving a maximum power
density of 50.2 W/m 3 . Zhang et al. [ 31 ] fabricated a low-cost and high-strength
activated carbon fiber (ACF) by using polyvinyl alcohol (PVA) fibers as the