Supplementary Material
Scanning electrochemical microscopy of graphene/polymer hybrid thin films as
supercapacitors: Physical-chemical interfacial processes
Sanju Gupta1 and Carson Price
Department of Physics and Astronomy, Western Kentucky University,
1906 College Heights Blvd., Bowling Green, KY 42101-3576 (USA)
GO was prepared by acid oxidation of natural kish graphite (Graphene Supermarket,
Austin, Texas) following modified Hummer’s method.1 The GO sheets are dispersed in deionized (DI) water to form a stable dispersion (1 mg/mL) and sonicated in an ultrasonic bath
(VWR model M1800) for 30 min. PPy was electrochemically polymerized onto ITO glass
stubstrates in a solution containing 0.25 M pyrrole and 0.4 M NaClO4 using a potentiodynamic
cyclic voltammetry (CV) mode from -0.5 V to 1.1V at a scan rate of 0.01 V/s for 5 cycles. Upon
scanning the positive potential, the electro-oxidation of monomer, Py, and subsequent polymer
deposition commences. As-prepared PPy films were air dried and GO dispersion was drop cast
onto PPy film and allowed to dry at room temperature. The resulting (PPy/GO)1 bilayer was
placed in an aqueous solution containing 1M NaCl (pH = 12.1) for electrochemical reduction of
top GO layer that took place in potentiostatic mode at 0.9 V for 1200 s forming (PPy/ErGO)1
single bilayer. Likewise, polyaniline (PAni) was electrochemically polymerized in a solution
containing 0.5 M alinline and 1M H2SO4 as oxidant in CV mode from 0.6 V to 1.4 V at a scan
rate of 0.1 V/s for 10 cycles. The rest of the procedure was similar to PPy as decribed above
resulting in (PAni/GO)1 and (PAni/ErGO)1 single bilayers. This process of polymerization, GO
*
Author to whom the correspondence should be made. E-mail address: sanju.gupta@wku.edu.
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dropcasting, and electrochemically reduction of GO resulting in ErGO was repeated as needed to
prepare hybrid multilayer supercapacitors. All of the potential are with respect to Ag/AgCl
reference electrode. The extent of GO reduction is assessed by monitoring G band in Raman
spectroscopy which tends to decrease from > 1600 cm-1 in GO to < 1592 cm-1 in ErGO.
All of these novel hybrids are characterized using scanning electron microscopy (Model
JEOL 5400LV, MA) operating at primary acceleration voltage (Vacc) of 10 kV with constant
current of 45 A in secondary electron imaging mode revealing surface morphology. Samples
for transmission electron microscopy (TEM) were prepared by placing one to two drops of
hybrids dispersion in ethanol on commercial lacey carbon Cu grids (Ted Pella Inc. CA) and
allowing it to air dry. TEM measurements were acquired (Model JEOL 1400Plus) at 100 kV and
1 nA yielding nanoscale structured. The room temperature electrical measurements (I-V) were
obtained with Keithley 2400 source meter (Keithley, OH) with two-electrode configuration that
provided resistance behavior (see Fig. S1). The contacts were made with colloidal silver paste
and a Cu wire. A asymmetric three-electrode cell configuration was custom-designed for
electrochemical measurements using Potentiostat/Galvanostat electrochemical workstation (CH
Instruments Inc., Model 920D, Austin, TX). A saturated Ag/AgCl (3M KCl) electrode and Pt
wire of 3 mm diameter were used as the reference and counter electrode, respectively. The
(PPy/GO)1, (PPy/ErGO)1, (PAni/GO)1, and (PAni/ErGO)1 hybrid films were used as the working
electrode. CV was performed in 1M KCl aqueous electrolytes within the potential range of 0.4
V and +0.6 V at room temperature at a scan rate of v = 100 mV/s. The SECM measurements are
carried out using CH Instruments Inc. Model 920D in probe approaching and feedback modes.
For SECM we used a Pt microelectrode (8-10 m) as the probe working electrode (tip) and 10
mM FeMeOH (ferrocene methanol) as redox mediator in support electrolyte 1M KCl for
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detecting kinetic differences. FeMeOH has a standard potential E0 = 0.21 V versus Ag/AgCl
similar to K3Fe(CN)6, (potassium ferricynaide) thus the Pt tip electrode was held at potential of
Vt = -0.1 V to ensure complete diffusion-limited oxidation of Fe(II) species originally present in
the electrolyte solution to Fe(III). The supercapacitor electrodes were biased at VS = 0.4 V or 0.2
V to ensure complete reduction of the species generated at the tip. The tip was scanned over the
working electrode surface area (400 m x 400 m and 600 m x 600 m) at a constant tipsubstrate separation of  10 μm to generate a feedback image with an approximate resolution of
tip radius.
Figure S1 (Color online). Room temperature current versus voltage (I-V) plots for
graphene/polymer hybrids displaying semiconducting (non-ohmic or nonlinear) behavior.
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Figure S2 (Color online). Shown are (a) zoomed out region of the solid/liquid interface along
with (ultra) microelectrode (UME) tip as working (WE), counter (CE) and reference (RE)
electrodes, (b-d) schematics of feedback modes during oxidation of Redox (R/O) species at the
tip positioned for a substrate include positive and negative feedback at a conductive and
insulating substrate based on hindered hemispherical diffusion, respectively (Adapted from Ref.
[2]).
1
W. S. Hummers and R.E. Offman, J. Am. Chem. Soc. 80, 1339 (1958).
L. Brunsweld, B. J. B. Folmer, E. W. Meijer, and R. P. Sijbesma, Chem. Rev. 101, 4071
(2001).
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