Civil Engineering Reference
In-Depth Information
composite gives an unique advantage for its use as proton exchange membrane (PEM)
in a low temperature fuel cell. A typical proton exchange membrane (also called a poly-
mer electrolyte membrane) fuel cell consists of a PEM with catalyst layer, gas dif usion
layer and electrodes on either sides of the PEM, shown schematically in the Figure
17.19 . h e fuel, H
2
gas, is catalytically oxidized on the anode surface to produce H
+
ions, which dif use across the PEM to get reduced to H
2
O at the cathode. Since the
PEM is an electrical insulator, electrons l ow to the cathode via the external load. h e
oxidation and reduction of hydrogen at the anode and cathode require the presence
of catalysts such as Pt, Pd or Pt-based alloy nanoparticles. In conventional PEM fuel
cells, Nai on membrane, which has high proton conductivity, is used as the exchange
membrane. However, it has serious disadvantages such as loss of proton conductivity
at elevated temperatures, dii cult synthesis process and high cost. Apart from Nai on,
phosphoric acid-incorporated polymer complexes such as poly(vinylalchol), polybenz-
imidazole, poly(silamine), and poly(ethylene imine) have been known to exhibit pro-
ton conductivity in the presence of water [63]. Hence these are also used in fuel cells.
Bacterial cellulose with its highly porous network structure alone treated with
H
3
PO
4
or Phytic acid (C
6
H
18
O
24
P
6
) exhibits properties required of proton conduct-
ing membranes. Jiang
et al.
[64] investigated the proton conductivity of acid-treated
BC composites. h ey found that proton conductivity reaches a maximum of 0.15 and
0.08 Scm
-1
for H
3
PO
4
- and PA-treated BC respectively. Although the modulus of BC
decreased due to acid treatment, it was still comparable to that of Nai on membrane.
h e performance of a fuel cell made with this membrane was studied by using Pt-coated
carbon paper as the electrodes. A maximum power density of 18 and 24 mWcm
-2
was
obtained for H
3
PO
4
- and PA-treated BC membrane fuel cell respectively (Figure 17.20
a and b). h ese results clearly demonstrate the potential of acid-treated BC as a proton
conductor in the fuel cell.
h e ability of using metal nanoparticles-loaded BC as catalyst and acid-treated BC
as the membrane to fabricate a purely BC-based fuel cell was demonstrated by Evan
et al.
and Yang
et al.
[65,66] . Evan
et al.
used Pd nanoparticles-loaded BC as the cat-
alyst layer and KCl-treated BC as proton conducting membrane to fabricate a fuel
cell which is only 150 μm thick (Figure 17.21 a). h in Pt-wires inserted into the Pd
+
-
V
e
-
e
-
Cathode
Anode
H
+
Gas difusion layer
Catalytic layer
Proton conducting
membrane
Figure 17.19
Schematic showing a polymer electrolyte fuel cell and the various components.
