Transcript finalpresv2

Hydrogen Peroxide Detection Using
Biogenic and Synthetic MnO2
Shu Feng, Jim Nurmi, Paul Tratynek
Satya Chinni, Brad Tebo
Department of Environmental and Biomolecular Systems
OGI School of Science and Engineering
Oregon Health & Science University
H2O2 Detection with MnO2 Electrodes
• Cyclic Voltammetry (CV)
2H2O2  O2 + 2H2O
– Voltage is applied across a
working electrode and a
counter electrode, scanning
between 0 and 1.2 V.
– When oxidation or reduction
occurs, the current increases,
causing a peak.
– With cyclic voltammetry
using a MnO2 electrode,
H2O2 is oxidized at ~0.7 V,
creating a current peak when
H2O2 is present.
H2O2 Detection with MnO2 Electrodes
• Chronoamperometry (CA)
– In chronoamperometry,
voltage is held constant and
current is recorded.
– Since in the CV the current
peak caused by H2O2
occurred around 0.7 V,
the voltage is held at 0.7 V
and H2O2 is added at
regular intervals.
– Plateau height of current is
linear to concentration of
H2O2 in cell.
Electrode Designs
• Gold Micron-Cavity
Powder Disk Electrode
– Difficult to make sure
MnO2 powder is well packed
– Background signal of the
gold is much higher than the
signal with MnO2 packed
Background signal
of gold electrode
Signal of MnO2
• Wax-Impregnated Graphite
Electrode
Peak from H2O2
No H2O2 present
– Difficult to control amount
of MnO2 on electrode, as
well as to control uniformity
of powder on the surface
Electrode Designs
• Glassy Carbon
Electrode with Spin
Coated MnO2
– Excess MnO2 solution is
pipetted onto the
electrode surface.
– By controlling spin
speed, an even coat can
be achieved.
– However, after a long
period of time in
solution, MnO2
eventually falls off.
Electrode Head
Spin Coating Apparatus
Close-up views of the electrode surface
Uneven MnO2
surface after time
in solution
Electrode Validation
• Standard Curve
– Addition of H2O2
consistently displays
linearity with current
plateau height.
– However, behavior of
electrode changes
over time and length
of exposure to H2O2.
Electrode Validation
• Standard Additions
– A sample of unknown
concentration is
injected into solution
and CA is run.
– Volumes of a standard
concentration are
injected to create a
calibration curve that
can be used to solve
for concentration of
the unknown.
Conclusions
• Gold micron-cavity powder disk electrode has a
high background signal from gold.
• Amount of MnO2 is difficult to control for on the
wax impregnated graphite electrode.
• Spin coated carbon electrode produces a evenly
coated electrode, but produces a varied response.
– Standard addition allows these electrodes to be
used as a sensor.
• Biogenic and synthetic MnO2 electrodes both have
H2O2 sensing capabilities, but the differences
between them need to be further studied.
Goals For Next Summer’s Intern…
(or me in the next week)
• Determine effects of aging of the electrode and MnO2 powder
• Further characterize electrode behavior in different electrolyte
conditions (pH, concentration, etc)
• More biogenic vs. synthetic MnO2 comparison
• Resolve problems with using sensor in seawater
Acknowledgments
Jim Nurmi
Paul Tratynek
Satya Chinni
Brad Tebo
Vanessa Green
EBS Department