Realizing Enzymatic Biofuel Cells
Through Nano
-Engineering
Nano-Engineering
Bor Yann Liaw
Electrochemical Power Systems Laboratory
Hawaii Natural Energy Institute
School of Ocean and Earth Science and Technology
University of Hawaii at Manoa
1680 East-West Road, POST 109, Honolulu, HI 96822
(808) 956-2339, [email protected]
The 4th US-Korea Forum on Nanotechnology, April 26, 2007, Hawaii
http://www.hnei.hawaii.edu
Enzymatic Bioelectrocatalysis
Dehydrogenase
Enzymes
BV: Benzyl Viologen
Cofactor
Mediator
6
6H+
zG.T.R.
Palmore, et al. J. Electroanal. Chem. 443 (1998) 155.
Alcohol Bio-Fuel Cells
H+
zEthanol
2 BV+
NAD+
Diaphorase
ADH
zAcetaldehyde
H2O
NADH
2 BV2+ 2e-
2 H+
H+
Anode
BV: Benzyl
Viologen
Proton
Conductive
Membrane
½ O2
Cathode
N.L. Akers et al. Electrochim Acta 50 (2005) 2521
zG.T.R.
Palmore, et al. J. Electroanal. Chem. 443 (1998) 155.
A Working Ethanol Bio-FC (EBFC)
t
u
lo
e
Fu
n
li
e
Fu
in
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
10
20
RE
30
40
2
50
60
Current (µA/cm )
V. Svoboda et al. (2006)
Anode cont.
xy
ge
n
ou
t
Nafion 112
O
xy
ge
n
Cathode cont.
O
Power (µW/cm2)
4.0
70
Issues Critical to EBFC
z
Power Density: Achievable power density is still far
below theoretical value
z Enhance enzyme loading
z Minimize conductive loss
Electronic conductive network
z Proton pathway
z
z Improve
charge transfer efficiency
Minimize transfer steps
z Promote direct transfer
z
z Facilitate
z
z
fluid transport
Pore structure engineering:
surface area vs. porosity •
dimensionality • directionality • interconnectivity of pores
Life (Stability)
z Micro chemical environment engineering
In Situ Characterizations
z
Enzyme loading: spatial distribution and local
(meso-scale) chemical environment
z Fluorescence imaging
z
Tagged enzymes
z Fluorescence
z
z
polarization
Reaction kinetics: temporal resolution
z Electrochemical imaging ellipsometry + QCM
Mass transport
z In situ characterization of permeability relative to
direction of flow
z Porosity, pore/channel size, accessible surface
area
Need for In Situ Characterizations
z
z
z
In today’s nano-material and bioengineering
research, control of materials synthesis and
process require fast, non-intrusive, in-situ
characterization over a large sample area.
For enzymatic biofuel cell applications, such in situ,
non-intrusive observations are highly desirable.
Example:
z Imaging ellipsometry + quartz crystal microbalance
(QCM) + electrochemical techniques (e.g., CV, EIS),
to study nano-materials and their properties:
Microstructure & surface morphology
z Reaction kinetics
z
Electrode Kinetics
eNADH
e-
Enzyme
Loading
CH3COH
-
ADH
NAD+
H+
Charge Transfer
CH3COH
out
e
NADH
CH3CH2OH
dS Vmax • S
=
dt K M + S
They must be
calculated
independently
Mass
Transfer
CH3CH2OH
in
Probing Micro Environments
Fluorescent laser scanning
confocal microscope (LSCM)
images of co-immobilized
Alexa-labeled dehydrogenase
(green) and TAMRA-labeled
lysozyme (red) in (A) Eastman
AQ 55 (B) chitosan. (Scale
bars: 50 µm.)
A. Konash et al. J Mat. Chem. 16 (2006) 4107.
A
B
C
LSCM images of ADH
tagged with Alexa-488
entrapped in (A) Eastman
AQ 55 polymer matrix: 2-D
slice; (B): 3-D
reconstruction from 2-D
slices; (C): Nafion: 2-D
slice. (Scale bars: 50 µm.)
Micro and Nano Materials Synthesis
z
e-
Develop highly porous conductive polymer
matrices:
z High enzyme loading
z Effective mass transport
z Highly conductive network
z Favorable micro environments for immobilization
10 µm
1 µm
5 µm
Polypyrrole (PPy) porous nano-fabrics, V. Svoboda et al. (2006)
Macro & Meso Pore Structure
Engineering
180
160
140
d (µm)
120
a
b
100
80
60
d
40
d = -125.8*t^-0.6464+171.4
20
0
0
1
2
3
4
5
6
7
8
9
Time (h)
c
d
Scaffolds made from 1 wt% chitosan in
0.4 M acetic acid solution frozen under
different durations: (a) 2 h, (b) 4 h, (c) 6
h, and (d) 8 h; scale bars = 200 µm.
Correlation of mean pore size d
versus freezing duration
M. Windmeisser et al. (2006)
10
DET in PQQ-GDH-Chitosan-CNT
b
20 mV/s
0.4
a
0.6
CHIT-CNTs-GDH
A
0.0
0.4
A
0.2
0.2
0.4
500
0.6
-0.2
0.5
0.2
-0.4
0.4
550
600
650
700
750
λ/nm
CHIT-CNTs
νDCIP=0.0111 mM/min
A=0.6394-0.1584*t
A
i/µA
CHIT-CNTs
0.6
CHIT-CNTs-GDH
0.3
0
-0.4
-0.2
0.0
0.2
E/V(vs.Ag/AgCl)
CV of (a) PQQ-bound CHIT/GCE and
(b) PQQ-bound CHIT-CNT/GCE in
0.1 M PBS at 20 mV/s
D.M. Sun et al. (2007)
0.4
0
1
2
t/min
3
1
4
2
t/min
3
4
Kinetic curves of CHIT-CNT and PQQGDH-bound CHIT-CNT films in 0.1 M
PBS with 0.1 M glucose, 0.8 mM PMS
and 0.02 mM DCPIP. Insets: (left) linear
fit plot and (right) the absorbance
spectra of DCPIP at 600 nm with PQQGDH-bound CHIT-CNT film with time
Imaging Ellipsometry (IE)
Live microscopic laser contrast image
( 600 × 400 µm )
1) Locate region-of-interest
2) Real-time laser image
observation via CCD
camera
3) Measurement of ∆ and Ψ
in spatial distribution
(600×400 µm)
Polypyrrole Deposition
z
z
Electrochemical Deposition & Control
z Fabrication conditions
Imaging Ellipsometry
z Film thickness
V. Svoboda et al. (2005)
z Surface morphology
0.5 mA/cm2
1 mA/cm2
Nafion
2 mA/cm2
z
Electrochemical
Deposition & Control
z Fabrication conditions
Imaging Ellipsometry
z Film thickness
z Surface morphology
40
80
Thickness = -0.0074 c3 + 0.1969 c2 + 1.0279 c - 0.1632
R2 = 0.9998
35
Thickness (nm)
z
70
30
60
25
50
20
40
15
30
10
20
MG Layer Thickness
Cumulative Charge
5
10
0
0
0
2
4
6
8
10
12
14
Cumulative Charge (mA·sec·cm-2)
Poly-MG Modified Surface
16
Cycle #
CV deposition of MG
on Pt
–0.5 V ÅÆ 1.2 V
(vs. Ag/AgCl)
Scan rate: 50 mV/sec
V. Svoboda et al.
J. Electrochem. Soc. 154 (2007) D113.
Nafion
Electrochem. Microgravimetric IE
ou
rce
Po
la
rs
O
se
er
yz
al
e
An
ti v
ec
bj
La
riz
Co
er
mp
en
sa
to
r
EP3 Imaging Ellipsometer
D
CC
te
de
ct o
r
CE with
degassing channel
ow
wind
win
dow
WE on
QCM
crystal
RE
QCM crystal holder
Solartron SI 1287
CV
Maxtek
QCM
QCM
EP3
Current & Mass Changes
(MM)
-2.5
-2.0
4
-1.5
M1
Mass
3
-1.0
d(mass)/dV
2
M5
M4
M3
M2
1
-0.5
0.0
1
0.5
0
1.0
-1
Current
1.5
-2
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Voltage vs. Ag/AgCl (V)
-0.2
-0.4
-0.6
-2
5
Current density (mA뷵m )
-2
Mass (µg뷵m )
-2
-1
2.3 - d(mass) / dV (µg뷵m 븉ec )
6
Current & Ellipsometric Angles
Current
0.0
34.0
-2
0.5
Current density (mA뷵m )
-1
- d(Ψ) / dV + 3.2 (deg븉ec )
34.5
1.0
33.5
1.5
Ψ (deg)
33.0
P1
Ψ
32.5
P2
2.0
2.5
32.0
129
1.0
∆ (deg)
125
D1
1.5
124
Delta
123
2.0
122
d(delta)/dV
2.5
121
D4
120
D6
D3
D2
1.0
D5
0.8
0.6
0.4
0.2
0.0
-0.2
Voltage vs. Ag/AgCl (V)
4
2
0
3.0
119
1.2
6
-1
126
-0.4
3.5
-0.6
-2
P3
P5
31.0
d(∆) / dV (deg븉ec )
0.5
3.5
P4
8
-2
127
3.0
P6
31.5
0.0
Current density (mA뷵m )
128
Current
d(Ψ)/dt
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Voltage vs. Ag/AgCl (V)
P2
4.0
-0.2
-0.4
-0.6
Reduction of MG to l-MG
Reduction of MG
Adsorption
Faraday’s law
M
•Q
F •n
T
M
i (t ) dt
m=
∫
F •n 0
m=
dm (t )
M
=
i (t )
dt
F •n
¾ In the reduction phase: the mass deposition was driven by
adsorption, followed by electrochemical reduction of MG to l-MG
Mass & ∆
¾ The progression of ∆ and d(∆)/dt follows mass changes.
Mass, Current, & Ψ
¾ The progression of Ψ and d(Ψ)/dt reflect both mass and chemical
changes in the film.
Conclusion
z
z
z
z
Enzymatic bio-fuel cells need delicate optimization
of electrode fabrication, which requires pore
structure engineering, from macro- to meso-scale.
Nano-material synthesis and electrode fabrication
require in situ observations and non-intrusive
characterizations of the process.
Several intriguing in situ characterization
techniques were demonstrated of their utility:
z Fluorescence and polarization
z Imaging ellipsometry + QCM + Electrochem. tech.
z Microporometry
Dynamic transient observations Æ mechanistic
details
Acknowledgements
z
Funding Support:
z ONR, Hawaii Environmental and Energy Technologies (HEET)
initiative (R. Rocheleau, PI)
z DCI Postdoctoral Fellow Research Program
z AFOSR, MURI Program (P. Atanassov, PI)
z
Contributors:
z Faculty: Michael Cooney, David Jameson, Shelley Minteer
z Postdocs: Wayne Johnston, Forest Quinlan, Vojtech
Svoboda, Stacey Konash, Dongmei Sun, Daniel Scott
z Students: Chris Rippolz, Mona Windmeisser, Swati Nagpal,
Ruey Hwu, Eric Brown
Thank you for your attention!