22.2.2 Application in Energy Harvesting
Printable and flexible enzyme-based electrodes platforms have proven to be efficient in
energy harvesting; biofuel cell applications. Usually, the glucose oxidase enzyme is used
as a bioreceptor on these electrodes for glucose biofuel cells. Off lately, our group has
been working extensively to design various paper-based, bioelectrodes for energy har
vesting. For instance, Rewatkar et al. developed a microfluidic paper-based Y-shaped
microchannel device with bucky paper bioelectrodes modified using glucose oxidase and
laccase enzyme as bioreceptors. The device has bioanode and biocathod. Bucky paper
electrodes were made with size 15 mm × 8 mm, they were cleaned with isopropyl alcohol.
These electrodes were dipped in a linker solution of EDC/NHS. Enzyme solutions were
prepared by weighing 5 mg of enzymes separately in 1 mL of 0.1 M PBS. The electrodes
were immersed in these enzyme solutions for about 2 hours. Bioanode was dipped in
glucose oxidase and laccase on biocathode. These prepared electrodes were then in
tegrated over a paper Y-shaped microchannel. The total size of this µPAD fuel cell device
was 50 mm × 25 mm. The device gave a maximum power density of 100 µW/cm2
(600 µA/cm2) at 0.505 V for about 50 hours. Figure 22.6 is the reprint of their device [15].
They also developed buck eye composite buckypaper bioelectrodes for developing en
zymatic biofuel cells using glucose oxidase and laccase enzyme. This device gave a large
current density of 9.79 mA/cm2 at 0.4 V and 2 mA/cm2 at 0.3 V using 40-mM of glucose
and a scan rate of 10 mV/s [33]. Nath et al. from our group reported paper-based mi
crobial biofuel cells using Escherichia coli carbon nanotube-buckypaper electrode. Bucky
paper of dimensions 15 mm × 8 mm was cut as bioelctrodes. Further, these were cleaned
with isopropyl alcohol and modified with multiwalled carbon nanotubes. A T-shaped
microchannel with a single outlet and two outlets was made. One inlet was used for
feeding bacterial solution and the other for oxygenated water. The electrodes were placed
near the edge of both channels. A 3D printed mini platform was designed to assemble
these electrodes. The platform had provisions for electrolytes. The device showed a
power density of 20 µA/cm2 at 0.405 V with 200 µL volume of culture [34].
Jayapriya et al. also demonstrated the fabrication of flexible electrodes using polyimide
sheets and CO2 laser ablation. These give laser-induced graphene which was further used
for enzymatic fuel cell application. Polyimide sheet was clenched to the glass slide. A
virtual design of microchannel was fed through the software. The CO2 laser of optimized
power and speed was made to ablate the sheet. About 80% of it was burnt. The burnt area
was removed to get a channel of 100 µM depth. The same approach was used for fab
rication laser-induced graphene (LIG) electrodes, modified with enzymes for studying the
energy harvesting application [18]. They also fabricated a 3D-printed, enzymatic micro
fluidic fuel cell device. Polylactic conductive filament with graphene composite was used
as electrodes. A Y-shape device was made of two parts. The device gave a power density
of 4.15 µWcm−2 and a current density of 13.36 A/cm2 [35].
Rewatakar et al. also fabricated a shelf-stacked, paper-based, Y-shaped microfluidic
device. It had bucky paper and carbon nanotube electrodes immobilized with glucose
oxidase and laccase enzymes. This gave a power density of 58 µA/cm2 at 0.8 V.
Figure 22.6B gives the real image of their device reprinted [16]. The same author also
developed automated, 3D printed, graphene and polylactic acid filament electrodes
modified with glucose oxide and laccase enzyme for biofuel cell study. This gave current
density of 1.41 mA/cm2 at 0.5 V (bioanode) using 40 mM glucose and 0.216 mA/cm2 at
0.42 V (biocathode). Figure 22.6C is the real image of their electrodes reprinted [17].
Jayapiriya et al. developed a microfluidic enzyme-based biofuel cell using laser-ablated
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