Stainless steel alloys woven mesh electrode and expanded mesh were
evaluated for their suitability as cathodes in Microbial electrolysis cells.
The meshes were prepared for use in the MECs by cutting metal mesh sheet in
3.8cm diameter discs with an exposed projected surface area of 7cm2. 12 SS 304
mesh of different sizes, a flat plate of SS 304 and lab made carbon cloth with
a platinum catalyst.
Three electrode LSV system comprises of a working cathode, a
counter electrode – platinum plate with a projected surface area of 2 cm2 and
Ag/AgCl reference electrode. The performance of flat stainless steel and
variety of stainless steel 304 mesh were evaluated on the basis of voltage
required to initiate hydrogen production.
Active surface areas of different stainless steel mesh were
determined by cyclic voltammetry by using a ferrocyanide solution. A solution
of 5mM K4Fe(CN)6 containing 0.2M Na2SO4 deoxygenated with ultra high purity
nitrogen for half hour was kept in the reactor shown in the LSV method with a
Pt/C cathode as the counter electrode. Cathode was wet-proofed carbon cloth
with a surface area of 7cm2 and platinum catalyst. The reactor was configured
and filled with solution in an anaerobic glove box to prevent oxidation ferrous
ion.
The MEC used for mesh comparison was a single cell cubic
reactor. This reactor is developed from a solid block containing a cylindrical
chamber. Anode was an ammonia processed graphite brush length.
MECs were operated in fed-batch mode. To prevent gas
accumulation between mesh cathode and end plate, a part of the top of mesh was
cut off and bent into the solution to assure no surface area loss. Whole gas
developed at the cathode as gathered into an anaerobic gas collection tube
glued to the top of the cubic reactor. The gas collection tube was sealed by a
rubber stopper and aluminium crimp cap. Gas development was measured by using a
respirometer.
A power source was used to apply voltage from 0.6 – 1.2 V to
the MECs. To enhance the functionality
of MEC, tree types of sandwich type electrodes were used to reduce electrode
spacing. Anode electrodes were heat processed carbon mesh. The cathodes were
stainless steel mesh. The difference among three electrode arrangements was the
separators kept between two electrodes. First type of separators was glass
fiber mats with thickness of 1mm. Another type was round hole perforated
plastic separator. Another type construction used double pieces of a small
plastic separator stated aove to support the top and bottom of electrodes,
creating an empty space between the electrodes.
The composition of MEC headspace and gas bags were tested by
using gas chromatography. Nitrogen, hydrogen and methane were tested with gas
chromatograph and CO2 with a separate GC. Nitrogen gas was a dilution gas and
hence it as eliminated in the calculations to find the contents of H2, CH4 and
CO2 developed by the system. Woven mesh electrode was found to be more effective in
increasing current than expanded mesh. It was also a more effective catalyst
for hydrogen evolution in MECs and used in further studies.
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