Pulsed galvanostatic deposition of Pt particles on microcrystalline and nanocrystalline diamond thin-film electrodes I. Characterization of as-deposited metal/diamond surfaces

Article abstract of DOI:10.1149/1.1890745

The pulsed galvanostatic deposition of nanometer-sized Pt particles on electrically conducting microcrystalline and nanocrystalline diamond thin-film electrodes is reported. The deposition was studied as a function of pulse number (10-50) and current density (0.50-1.50 mA cm^-2) at the two morphologically different forms of diamond. The deposition of catalyst particles using ten 1 s pulses (duty cycle 50%) at a current density of 1.25 mA cm ^-2 (geometric area) produced the smallest nominal particle size and the highest particle coverage on both diamond surfaces. Secondary electron micrographs revealed metal particle deposition over much of the diamond surface, a nominal particle size of 43 ± 27 nm [relative standard deviation (RSD) = 63%] for microcrystalline and 25 ± 25 nm (RSD = 100%) for nanocrystalline diamond, and a nominal particle coverage of 7.5 (±0.9) × 109 cm^-2 for microcrystalline and 1.9 (±1.0) × 10¹⁰ cm^-2 for nanocrystalline diamond. Deposition under these conditions resulted in the most efficient utilization of the metal catalyst for H⁺ adsorption, based on the electrochemically active Pt area normalized to the estimated metal loading. Typical specific surface areas of 10-50 m²/g Pt were calculated, which compare favorably to values obtained at sp² electrodes, like carbon and graphite. The influence of the diamond electrode microstructural and electronic properties on the formation of dimensionally uniform metal adlayers is discussed.

Full text of DOI:10.1149/1.1890745

E184
Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
0013-4651/2005/152͑5͒/E184/9/$7.00 © The Electrochemical Society, Inc.
Pulsed Galvanostatic Deposition of Pt Particles
on Microcrystalline and Nanocrystalline Diamond
Thin-Film Electrodes
I. Characterization of As-Deposited Metal/Diamond Surfaces
*
**,z
Jason A. Bennett, Yoshiyuki Show, Shihua Wang, and Greg M. Swain
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824-1322, USA
The pulsed galvanostatic deposition of nanometer-sized Pt particles on electrically conducting microcrystalline and nanocrystalline
diamond thin-film electrodes is reported. The deposition was studied as a function of pulse number ͑10-50͒ and current density
͑0.50-1.50 mA cm−2͒ at the two morphologically different forms of diamond. The deposition of catalyst particles using ten 1 s
pulses ͑duty cycle 50%͒ at a current density of 1.25 mA cm−2 ͑geometric area͒ produced the smallest nominal particle size and the
highest particle coverage on both diamond surfaces. Secondary electron micrographs revealed metal particle deposition over much
of the diamond surface, a nominal particle size of 43 ± 27 nm ͓relative standard deviation ͑RSD͒ = 63%͔ for microcrystalline and
25 ± 25 nm ͑RSD = 100%͒ for nanocrystalline diamond, and a nominal particle coverage of 7.5 ͑±0.9͒ ϫ 109 cm−2 for microc-
rystalline and 1.9 ͑±1.0͒ ϫ 1010 cm−2 for nanocrystalline diamond. Deposition under these conditions resulted in the most effi-
cient utilization of the metal catalyst for H+ adsorption, based on the electrochemically active Pt area normalized to the estimated
metal loading. Typical specific surface areas of 10-50 m2/g Pt were calculated, which compare favorably to values obtained at sp2
electrodes, like carbon and graphite. The influence of the diamond electrode microstructural and electronic properties on the
formation of dimensionally uniform metal adlayers is discussed.
© 2005 The Electrochemical Society. ͓DOI: 10.1149/1.1890745͔ All rights reserved.
Manuscript submitted May 31, 2004; revised manuscript received October 1, 2004. Available electronically April 11, 2005.
Carbon-supported metal catalysts are widely used in electro-
as an advanced carbon electrocatalyst support material.18-21 There
are two technical challenges in this endeavor: development of elec-
trically conducting diamond ͑e.g., powder͒ with high surface area
and establishment of a protocol for depositing and stabilizing highly
dispersed electrocatalyst particles on the diamond support. Thus far,
our efforts have been focused on the latter task with the goals of ͑i͒
determining the dimensional stability of diamond thin film ͑low sur-
face area͒ under a variety of electrochemical conditions19 and ͑ii͒
studying the formation of electrocatalytic Pt adlayers on the film
surface.20 Diamonds possess properties that make it an attractive
support material: dimensional stability, resistance to corrosion, and
the ability to operate for extended periods of time in harsh chemical
environments at high potential, current density, and temperature
without microstructural or morphological degradation.21,22
Two types of electrically conducting diamond thin film are under
investigation: microcrystalline ͑Ͼ1 ␮m crystallite size͒ and nano-
crystalline ͑ϳ10 to 20 nm crystallite size͒.23-28 Each possesses a
different morphology and microstructure, but both exhibit similar
electrical conductivity and electrochemical activity when highly
doped with boron. The formation of metal phases on polycrystalline
diamond has been reported.20,29-33 A common observation, though,
is weak attachment of the metal particles to the hydrogen-terminated
diamond surface.19,20,31,32 Consequently, the metal particles are
easily dislodged from the surface by gas evolution, for instance. In
an effort to better stabilize the metal particles, we have adopted an
approach whereby a short secondary diamond growth is applied to
the metal-coated surface. This secondary growth entraps the metal
particles into the surface microstructure without causing major loss
in the electrocatalytic activity. We refer to these as metal/diamond
composite electrodes.19-21 This sequential diamond growth/Pt
deposition/secondary diamond growth procedure produces a dimen-
sionally stable and electrically conductive catalytic electrode. The
metal catalyst particles are strongly anchored in the microstructure
by the secondary diamond growth. For instance, no morphological
or microstructural damage and no lost catalyst activity were ob-
chemical technologies. For example, dispersed Pt particles on high-
surface-area carbon supports are used as catalysts for hydrogenation
and oxidation reactions, such as for both hydrogen oxidation and
oxygen reduction in phosphoric acid ͑PAFCs͒ and proton exchange
membrane fuel cells ͑PEMFCs͒.1,2 Platinum is the best electrocata-
lyst for the oxygen reduction reaction ͑ORR͒, an important reaction
in biological systems and fuel cells.3-13 Among the carbon support
materials regularly employed, activated carbons are probably the
most common. Activated carbons possess a turbostratic microstruc-
ture of sp2-bonded carbon with
a high surface area and
microporosity.1,2 The properties of the electrocatalyst support mate-
rial are crucial for the operational performance.1-3,14,15 The primary
role of the support is to provide a high surface area over which
highly dispersed, nanometer-sized electrocatalyst particles can be
dispersed and stabilized. Highly dispersed supported catalysts are
attractive for electrochemical processes because a high electro-
chemically active surface area can be achieved with a low loading of
the normally expensive electrocatalyst.
As mentioned previously, current electrocatalyst support materi-
als are generally porous, sp2-bonded carbon materials ͑e.g., physi-
cally or chemically activated carbon or carbon black͒. These mate-
rials function well in many applications but are susceptible to
oxidation and/or corrosion in the presence of reactive oxygen, in
aggressive chemical environments and/or under harsh electrochemi-
cal conditions.1,2,15,16 The oxidation/corrosion causes morphological
and microstructural damage that leads to decreased catalytic activity
due to catalyst detachment, aggregation, and/or fouling by gasifica-
tion products. Complete electrode failure can result if the degrada-
tion is severe enough.
Advanced electrocatalyst support materials are needed for those
demanding applications where conventional sp2-bonded carbon sup-
ports fail. One example of this occurs in fuel cells during start-up
and shut-down as a local cathode potential as high as 1.5 V can be
reached, which is a potential well positive of the thermodynamic
value.17 Carbon corrosion can occur at such high voltages and this
leads to degradation of the stack voltage. Our group has been inves-
tigating the use of electrically conducting polycrystalline diamond
served after two 1 h periods of anodic polarization in 85% H3PO4 at
19
170°C and 0.1 A cm−2
.
In comparison, a Pt-impregnated sp2 car-
bon cloth electrode ͑E-Tek͒ failed catastrophically within the first
few minutes of exposure to the same conditions.
We have previously studied the formation of Pt adlayers on dia-
mond by dc magnetron sputtering18 and electrodeposition, both con-
stant potential and current.19,20 Electrodeposition is the preferred
method of the two because it affords better control over the particle
*
Electrochemical Society Student Member.
Electrochemical Society Active Member.
**
z E-mail: swain@chemistry.msu.edu
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
E185
size and coverage. Despite the excellent dimensional stability of the
Pt/diamond composite electrode, the nominal Pt particle size pro-
duced was too large and the coverage too low to be practical. For
example, the particle size varied from 50 to 300 nm and the particle
coverage was in the 108 cm−2 range for metal phase formation at
constant current.19,20 Low loadings of highly dispersed metal par-
ticles are desired for a practical supported catalyst. Pulsed galvano-
static deposition can produce metal particles that are nominally
smaller in size and more uniformly distributed over a surface com-
pared to what is achieved using constant current deposition. Pulsed
electrodeposition approaches have been employed to prepare
nanometer-sized particles of metals and alloys.33-45 Individual par-
ticle growth is favored as the conditions are selected to minimize
overlap of reactant depletion layers from neighboring particles.
Maintaining separate depletion layers around each particle results in
similar growth rates for all and leads to more highly dispersed par-
ticles of nominally smaller size.
We report herein on the use of pulsed galvanostatic deposition to
form Pt adlayers on both microcrystalline ͑BMD͒ and nanocrystal-
line ͑BND͒ diamond thin films. This work is a continuation of our
effort to control and understand metal phase formation on diamond.
The purpose for the work was to learn how the nucleation and
growth of Pt electrocatalyst particles on both diamond types is af-
fected by the pulse current density and pulse number. In particular,
the spatial distribution of the deposits over the surface, the nominal
particle size and variance, and the particle coverage were the factors
of interest. Another objective was to learn how the diamond film
morphology and microstructure affect the metal phase formation.
Polycrystalline diamond is a heterogeneous electrode material in
terms of its microstructural and electronic properties, which compli-
cates the study of metal phase formation. The microstructural and
electronic properties certainly play a key role in the kinetics of metal
electrodeposition and the time-dependent surface morphology of the
deposits. The uncoated and coated diamond electrodes were charac-
terized by scanning electron microscopy ͑SEM͒, cyclic voltamme-
try, and conductivity-probe atomic force microscopy ͑CP-AFM͒.
They were then gradually cooled over several minutes to less than
400°C in the presence of atomic hydrogen by reducing the micro-
wave power and system pressure. This postgrowth annealing in
atomic hydrogen serves to etch away adventitious nondiamond car-
bon impurity, minimize dangling bonds, and ensure maximum hy-
drogen termination. Both film types had a nominal boron dopant
concentration of ca. 1020 B cm−3 and a film resistivity of less than
0.05 ⍀ cm.
Electrochemical measurements.—All electrochemical measure-
ments were performed at room temperature in a single-compartment
glass cell using a CH Instruments model 650A electrochemical
workstation ͑CH Instruments, Inc., Austin, TX͒. The design of the
electrochemical cell was reported previously.46 The diamond elec-
trodes were pressed against the bottom of a glass cell. A Viton
O-ring was used to contain the solution and define the exposed
electrode area, 0.2 cm2. All currents are normalized to this area un-
less otherwise noted. An Ag/AgCl reference electrode was posi-
tioned in close proximity to the working electrode using a cracked-
glass capillary filled with 4 M KCl. All potentials reported herein
are referenced to this electrode. A large-area carbon rod served as
the auxiliary electrode and was positioned normal to the working
electrode. Electrical connection was made to the working electrode
by contacting the back side of the cleaned Si substrate with a clean
Cu plate. The clean Si surface was rubbed with a graphite rod prior
to contacting the Cu plate. Once mounted in the cell, the electrode
surface was cleaned by soaking in distilled 2-propanol for 20 min.47
The diamond films were characterized, prior to Pt deposition, using
several redox systems ͓Fe͑CN͒−3/−4, Ru͑NH3͒+3/+2, Fe+3/+2, and
6
6
IrCl−62/−3͔ to evaluate the electrode response over a wide potential
range, as reported elsewhere.27,28,46 All chemicals were reagent
grade quality or better, and used without additional purification. The
1 mM solutions of potassium ferrocyanide ͑Aldrich͒, hexaam-
mineruthenium͑III͒ chloride ͑Aldrich͒, and ferric sulfate ͑Fisher͒,
and the 0.1 mM solution of potassium hexachloroiridate͑IV͒ ͑Ald-
rich͒ were prepared fresh daily. The supporting electrolyte was ei-
ther 1 M KCl ͑Spectrum͒ or 0.1 M HClO4 ͑redistilled, 99.999%,
Aldrich͒. For most experiments, the solutions were first degassed by
bubbling N2 for at least 10 min, and then maintained under an N2
blanket during the measurement.
Experimental
Diamond thin-film deposition.—Microcrystalline and nanocrys-
talline diamond thin-film electrodes were deposited using
microwave-assisted plasma chemical vapor deposition ͑CVD;
1.5 kW, 2.54 GHz, Astex, Inc., Lowell, MA͒ on highly conducting
p-Si͑100͒ substrates ͑Ͻ0.001 ⍀ cm, Virginia Semiconductor, Inc.͒.
The substrates were pretreated by mechanical polishing on a felt
pad for 5 min using a 2 ␮m diam diamond powder ͑GE Super-
abrasives, Worthington, OH͒ slurried with ultrapure water ͑18 M⍀͒.
After polishing, the substrates were rinsed with ultrapure water
and 2-propanol. The substrates were then ultrasonically cleaned in
acetone, 2-propanol, and ultrapure water ͑5 min each͒. The micro-
crystalline films were deposited for 10 h using a methane-to-
hydrogen ͑CH4/H2͒ source gas ratio of 0.50%. The total gas flow
was 200 sccm with the microwave power, pressure, and tempera-
ture held constant at 1 kW, 45 Torr, and ϳ800°C, respectively.
The nanocrystalline films were deposited using gas flow rates of 1,
94, and 5 sccm for CH4, Ar, and H2, respectively. These films were
grown for ca. 2 h using a microwave power of 800 W, a deposi-
tion pressure of 140 Torr, and a temperature of ϳ800°C. All
gases were ultrahigh purity ͑99.999%͒ grade ͑CH4 and H2 from
AGA Specialty Gas, Cleveland, OH, and Ar from BOC Group, Inc.,
Murray Hill, NJ͒. The film thickness was 3-7 ␮m for both film
types.
After evaluating an electrode response, the cell was thoroughly
rinsed with ultrapure water and filled with 1 mM potassium
hexachloroplatinate͑IV͒ ͑98%, Aldrich͒ dissolved in 0.1 M HClO4.
The solution was purged with N2 for 20 min prior to deposition.
Nanometer-sized Pt particles were deposited under an N2 blanket
using the pulsed galvanostatic method. The hardware consisted of a
homemade galvanostat, configured from an OMNI 90 potentiostat
͑Cypress Systems, Inc., Lawrence, KS͒ that was interfaced with a
PCI-6034E controller and data acquisition board ͑National Instru-
ments, Austin, TX͒. The pulse generation was computer-controlled
using National Instruments LabVIEW software ͑version 5.1 or 6.0͒.
All pulses were 1 s in length with a 1 s delay time between each,
which is a 50% duty cycle ͑pulse time/period͒. The pulse number
and current density were systematically investigated to determine
the optimum deposition conditions in terms of metal particle size
and coverage.
After depositing the metal, the platinate solution was removed
and the cell was carefully rinsed with ultrapure water by flowing the
water down the sides of the glass cell. Metal particles generally
weakly adhere to the hydrogen-terminated diamond surface, and
vigorous rinsing can result in significant particle detachment. The
cell was then filled with a fresh 0.1 M HClO4 solution, again by
pouring the solution down the sides of the cell, and purged with N2
for 30 min. The gas was introduced far enough from the surface so
as to not disturb the catalyst particles. Under the N2 blanket, the
potential was cycled ten times between −200 and 1300 mV vs.
Ag/AgCl to clean the Pt deposits. The potential was kept within this
window to avoid significant gas evolution. The voltammetric i-E
curve usually stabilized within five cycles. The charge for H+ ad-
Both film types were doped from the gas phase by adding
10 ppm B2H6 ͓2.0 ͑microcrystalline͒ and 1.0 ͑nanocrystalline͒ sccm,
respectively, of 0.1% B2H6 diluted in H2, Matheson Gas Products,
Inc.͔ to the source gas mixture. Following the deposition, the CH4
and B2H6 flows were stopped, and the films remained exposed to
the H2 ͑BMD͒ or H2/Ar ͑BND͒ plasma for an additional 10 min.
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

E186
Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
sorption was used to determine the electrochemically active Pt sur-
face area, assuming a 1H:1Pt surface interaction and a coulombic
charge of 210 ␮C/cm2 for hydrogen adsorption on an atomically flat
Pt͑111͒ surface.48-50
Glassy carbon was used in some comparison measurements. The
electrode ͑GC-30, Tokai, Ltd., Japan͒ was mechanically polished on
separate felt polishing cloths using aqueous slurries of 1.0, 0.3, and
0.05 ␮m diam deagglomerated alumina powder ͑Buehler, Ltd., Illi-
nois͒. After each polishing step, the electrode was copiously rinsed
with ultrapure water and ultrasonically cleaned in this medium for
10-15 min. After the final polishing and sonication step, the elec-
trode was dried in a stream of N2 electrode and placed in the elec-
trochemical cell where it was exposed to distilled isopropanol for
10 min as a final cleaning step.
Physical characterization.—The films were physically charac-
terized using a JSM-6400V scanning electron microscope ͑JEOL,
Ltd., Tokyo, Japan͒. Micrographs were recorded using both second-
ary and backscattered electrons generated with an accelerating volt-
age of 20 kV. The presence of Pt was verified by energy-dispersive
X-ray ͑EDX͒ analysis ͑Noran Instruments, Inc., Middleton, WI͒ in
conjunction with the JSM-6400V. Particle analysis was performed
using the AnalySIS imaging software ͑Software Imaging System
Corp., Lakewood, CO͒.
CP-AFM measurements were carried out with a NanoScope IIIa
͑Veeco Instruments, CA͒. A Au-coated silicon tip was used in the
contact mode. A homemade electrical circuit was used to measure
the current flowing between the conductive tip and the electrode
surface as the tip was rastered over an area. The diamond samples
were placed on a metal stage and electrical contact was made to the
bottom of the conducting Si substrate using carbon tape. A bias
voltage was applied between the tip and the substrate, +2 V. Con-
ductivity maps were generated simultaneously with the topographi-
cal images.
Atomic absorption spectrometry ͑AAS͒ was used to determine
the catalyst loading for a given set of deposition conditions. For
these measurements, the Pt particles were deposited on a separate
set of diamond film as a function of the current density and pulse
number. After deposition, the Pt metal was then dissolved from
the electrode by soaking for 1 h in 4 mL of warm aqua-regia, which
consisted of 3 mL HCl ͑36.5-38.0%, Columbus Chemical Indus-
tries, Inc., Columbus, WI͒ and 1 mL HNO3 ͑70%, Columbus
Chemical Industries, Inc., Columbus, WI͒. Pt is known to dissolve
in warm aqua-regia while diamond is quite stable in this solution
and undergoes no morphological alteration.19,20 Upon cooling to
room temperature, the electrode was removed from the solution and
rinsed thoroughly with ultrapure water. The rinses were collected
and mixed with the original solution to collect all the dissolved
metal. The total solution volume was 50 mL. AAS was performed
directly on this solution using a Hitachi Z-9000 atomic absorption
spectrophotometer ͑Hitachi, Ltd., Tokyo, Japan͒ with a graphite tube
furnace. The metal ion concentration in each solution was deter-
mined from multiple measurements in order to estimate the metal
loading.
Results
Figure 1. SEM images ͑secondary electron͒ of Pt/BMD electrodes deposited
using ͑A͒ 10, ͑B͒ 25, and ͑C͒ 50 pulses, respectively. Pulse width 1 s. Cur-
rent density 0.50 mA/cm2.
Pt deposition on microcrystalline diamond.—Pt metal was de-
posited onto the diamond surface by pulsed galvanostatic deposition
with the pulse width and current density maintained constant at 1 s
and 0.50 mA/cm2 ͑geometric area͒, respectively, and a pulse num-
ber of either 10, 25, or 50. Figure 1a-c shows secondary electron
micrograph ͑SEM͒ images of Pt-coated microcrystalline diamond
thin-film electrodes for these three pulse numbers. EDX analysis
confirmed that the bright spots are indeed Pt particles. The particles
decorate both the grains and grain boundaries, indicating that most
regions of the polycrystalline film are electrochemically active and
support charge transfer. The formation of the multilayer islands or
deposition.39 Increasing the number of pulses leads to an increase in
the metal loading as more charge is passed; however, the nominal
particle size increases and the particle coverage decreases. These
trends are reflected in the Table I data. Depositing Pt with 10 pulses
yields a nominal particle diameter of 46 ± 27 nm ͓relative standard
deviation ͑RSD͒ = 58%͔ and a nominal particle coverage of
1.1 ͑±0.6͒ ϫ 109 cm−2. Increasing the number of pulses to 25 ap-
particles is consistent with
a Volmer-Weber mechanism of
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
E187
Table I. Particle analysis and hydrogen adsorption data for Pt-
coated microcrystalline diamond films as a function of the pulse
number.a
Mean
particle
size
Hydrogen
adsorption
charge
Particle
No. of
pulses
coverage
b
b
͑nm͒
͑cm−2
͒
͑mC/cm2͒
RF
10
25
50
46 ± 27
100 ± 85
105 ± 66
1.1 ͑±0.6͒ ϫ 109
9.8 ͑±4.4͒ ϫ 108
3.8 ͑±0.1͒ ϫ 108
0.066 ± 0.014
0.13 ± 0.014
0.21 ± 0.015
0.31
0.64
0.99
a Pulse width 1 s. Delay time 1 s. Current density 0.50 mA/cm2 ͑geo-
metric area͒. RF is the electrochemically active Pt area obtained from
the hydrogen adsorption charge normalized to the geometric area of
the diamond film ͑0.2 cm2͒.
b Values normalized to the geometric area of the diamond film.
proximately doubles the average particle diameter to 100 ± 85 nm
͑RSD = 85%͒ and halves the particle coverage to 9.8 ͑±4.4͒
ϫ 108 cm−2. Increasing the number of pulses to 50 slightly in-
creases the average particle diameter to 105 ± 66 nm ͑RSD
= 63%͒ and further reduces the particle coverage to 3.8 ͑±0.1͒
ϫ 108 cm−2. Careful examination of the images, in particular Fig.
1c, reveals that the particles are not smooth but rather are rough with
a dendritic morphology.
Figure 2 shows background cyclic voltammetric i-E curves in
0.1 M HClO4 for the Pt-coated microcrystalline thin-film electrodes
formed with different pulse numbers. The scans were initiated at
200 mV with the forward sweep in the positive direction at a rate of
50 mV/s. All the voltammetric features characteristic of clean poly-
crystalline Pt are observed. The total current response increases with
pulse number, which is consistent with an increase in the Pt loading.
Even though the nominal particle diameter increases and the cover-
age decreases, the electrochemically active Pt increases.50 The ex-
planation for this is that the microscopic roughness of the deposits is
increasing with pulse number, something that is evident in the SEM
images ͑Fig. 1͒. The well-defined voltammetric signatures for Pt
indicate that the metal particles are in good electrical communica-
tion with the current-collecting Si substrate through the boron-doped
diamond film. The H+ adsorption charge density, listed in Table I,
was found by integrating the cathodic current for this reaction be-
tween 100 and −190 mV vs. Ag/AgCl and correcting for the double-
Figure 3. SEM images ͑secondary electron͒ of Pt/BMD electrodes deposited
at pulse current densities of ͑A͒ 0.50, ͑B͒ 0.75, ͑C͒ 1.00, ͑D͒ 1.25, and ͑E͒,
1.50 mA/cm2, respectively. Pulse number 10. Pulse width 1 s. The scale bar
in each image is 1 ␮m.
layer charging current ͑see the shaded region of the i-E curve in Fig.
2͒. The electrochemically active Pt areas were calculated to be
0.062, 0.13, and 0.20 cm2, respectively, for 10, 25, and 50 pulses ͑all
electrodes possess the same deviation of ±0.016 cm2͒. Conse-
quently, the roughness factor ͓RF, the electrochemically active Pt
area/geometric area of the diamond electrode ͑0.2 cm2͔͒ increases
with pulse number, as is shown in Table I. It appears that the depo-
sition of Pt on existing Pt clusters occurs more facilely than on
the bare diamond surface, and this creates a greater microscopic
surface roughening with increasing pulse number. The loading in-
crease was confirmed by AAS with calculated values of 2.4, 3.3,
and 7.4 ␮g/cm2 ͑measured for just one film at each pulse number͒
for 10, 25, and 50 pulses, respectively. An important performance
parameter for electrocatalytic electrodes is the specific Pt surface
area, defined as the electrochemically active Pt area normalized to
the Pt loading. The specific surface areas were calculated to be 13,
20, and 14 m2/g Pt, respectively, for the three pulse numbers. Typi-
cal values for Pt electrocatalysts used in fuel cells are in the range of
100-200 m2/g Pt. Therefore, the specific surface areas on the planar
diamond thin-film electrodes are about a factor of ten lower than
what is desired for a fuel cell electrocatalyst.
The electrodeposition of Pt on microcrystalline diamond was
also investigated as a function of the pulse current density from
0.50 to 1.50 mA/cm2 ͑geometric area͒. The deposition was carried
out using a pulse number of 10 and a pulse width of 1 s. Increasing
the current density has the effect of increasing the activation over-
potential ͑␩͒. SEM images of metal-coated films are displayed in
Fig. 3a-e. Table II presents a summary of the particle analysis data.
Statistically, the nominal particle size is the same for all five current
densities, ranging from 40 to 70 nm with an RSD of approximately
50%. The particle coverage increases from 1.3 ͑±1.0͒ to
Figure 2. Cyclic voltammetric i-E curves in 0.1 M HClO4 for Pt/BMD
electrodes with Pt deposited using the different pulse numbers. Pulse width
1 s. Current density 0.50 mA/cm2. Scan rate 50 mV/s. The shaded region of
the curve represents the charge associated with hydrogen adsorption. The
current is normalized to the BMD geometric area, 0.2 cm2.
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

E188
Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
Table II. Particle analysis and hydrogen adsorption data for Pt-
Table III. The electrochemically-active Pt area, specific Pt sur-
face area, and roughness factor for Pt-coated diamond films de-
posited at different pulse current densities.a
coated microcrystalline diamond films as a function of the pulse
current density.a
Pulse current Mean particle
Particle
Hydrogen adsorption
charge
Pulse current
density
Estimated
loading
b
Electrochemically
active Pt area
͑cm2͒
Specific Pt
surface area
͑m2/g Pt͒
density
size
coverage
b
b
b
b
͑mA/cm2͒
͑nm͒
͑cm−2
͒
͑mC/cm2͒
͑mA/cm2͒
͑␮g/cm2͒
RF
0.50
0.75
1.00
1.25
1.50
46 ± 27
65 ± 37
59 ± 34
43 ± 27
68 ± 43
1.1 ͑±0.6͒ ϫ 109
1.5 ͑±0.4͒ ϫ 109
2.2 ͑±0.6͒ ϫ 109
7.5 ͑±0.9͒ ϫ 109
1.9 ͑±0.9͒ ϫ 109
0.066 ± 0.014
0.095 ± 0.0069
0.11 ± 0.0047
0.16 ± 0.0051
0.19 ± 0.031
0.50
0.75
1.00
1.25
1.50
2.4
2.3
2.2
3.4
4.3
0.062 ± 0.02
0.090 ± 0.007
0.11 ± 0.005
0.15 ± 0.004
0.18 ± 0.04
13
20
25
22
21
0.31
0.45
0.53
0.74
0.89
a Pulse number 10. Pulse width 1 s. Delay time 1 s.
a Pulse number 10. Pulse width 1 s. Delay time 1 s. Loading estimated
from AAS measurements of the dissolved metal deposits.
b Normalized to the geometric area of the diamond film.
b Values normalized to the geometric area of the diamond film.
7.5 ͑±0.9͒ ϫ 109 cm−2 with current density up to 1.25 mA/cm2.
For the highest current density, though, 1.50 mA/cm2, the particle
coverage decreases to 1.9 ͑±0.9͒ ϫ 109 cm2. The film deposited at
1.25 mA/cm2 has particles that are nominally the same size as those
produced at 0.50 mA/cm2, but with a particle density nearly six
times greater.
Figure 4 shows background cyclic voltammetric i-E curves for
the Pt-coated microcrystalline thin-film electrodes formed with dif-
ferent pulse current densities in 0.1 M HClO4. The scans were ini-
tiated at 200 mV with the forward sweep in the positive direction at
a rate of 50 mV/s. Again, all the voltammetric features characteristic
of clean polycrystalline Pt are present. There is a progressive in-
crease in the total voltammetric current as the deposition current
density is increased from 0.50 to 1.50 mA/cm2, indicating the elec-
trochemically active Pt area is increasing. The charge associated
with the H+ adsorption increases with deposition current density, as
shown in Table II. This is due to an increase in the particle coverage,
as is observed for the films coated at current densities from
0.50 to 1.25 mA/cm2, and the particle roughening.
Table III shows the estimated metal loading, the electrochemi-
cally active Pt area, the specific Pt area, and the roughness factor for
the Pt-diamond electrodes formed at different pulse current densi-
ties. The electrochemically active Pt area and roughness factor both
increase with deposition current density, as reflected in the voltam-
metric i-E curves. This is due to the increase in particle coverage ͑at
least up to 1.25 mA/cm2͒ and microscopic roughness of the par-
ticles. The apparent metal loading increases from 2 to 6 ␮g Pt/cm2
with deposition current density. The specific Pt surface area ranges
from 10 to 25 m2/g Pt with the values clustered around 20 m2/g Pt.
Platinum deposition on nanocrystalline diamond.—Pulsed gal-
vanostatic deposition was also used to form Pt adlayers on boron-
doped nanocrystalline diamond electrodes. Metal deposition is a sur-
face “sensitive” charge-transfer process; therefore, the morphology
and microstructure can strongly influence the nucleation mechanism.
Comparing the deposition at these two diamond types provides in-
sight about the influence of the film microstructure and morphology
͑e.g., grain boundaries, defects, facets, etc.͒ on the metal phase for-
mation.
Two deposition conditions were evaluated, ten 1 s pulses at 0.50
and 1.25 mA/cm2. SEM images of these two metallized surfaces are
shown in Fig. 5a ͑0.50 mA/cm2͒ and B ͑1.25 mA/cm2͒. Nanocrys-
talline diamond has a much smoother surface morphology than does
microcrystalline diamond and a larger fraction of exposed grain
boundary due to the smaller aggregate size.26,27 It is also as corro-
sion resistant. The morphology consists of ca. 100 nm clusters of
individual diamond crystallites that are 10-15 nm in diameter. We
supposed that the higher fraction of grain boundary might lead to a
higher nucleation site density for Pt and, in turn, to smaller particles
with higher coverages. Other related work in our laboratory has
demonstrated that this is in fact the case, as nanocrystalline outper-
forms microcrystalline diamond for the anodic stripping voltammet-
ric determination of dissolved metal ions, in part, because metal
phase formation on the former occurs with lower particle size and
higher coverage.51 The SEM images reveal metal deposits on the
diamond surface, many of which appear to be located at the grain
boundaries. Particle size analysis revealed a nominal diameter of
72 ± 41 nm ͑RSD = 57%͒, which is statistically similar to the par-
ticle size seen for microcrystalline diamond at the same current
density. The particles are not as uniformly distributed over the sur-
face as they are on the microcrystalline diamond surface, at least
under these deposition conditions. The uneven distribution is re-
flected in a lower particle coverage of 6.1 ͑±4.6͒ ϫ 108 cm−2
,
which is an order of magnitude less than that seen for the microc-
rystalline film.
The metal particles formed at 1.25 mA/cm2 have a smaller
nominal size of 25 ± 25 nm ͑RSD = 100%͒. The Pt particles are
also more uniformly distributed over the surface and this is reflec-
ted in a larger particle coverage of 1.9 ͑±1.0͒ ϫ 1010 cm−2
.
Many of the metal particles appear to reside at the grain boundaries,
which is consistent with these regions being the primary nucle-
ation sites. This particle coverage is the highest observed for any
of the diamond films under study, microcrystalline or nanocrystal-
line.
Figure 6 shows background cyclic voltammetric i-E curves in
0.1 M HClO4 for Pt-coated nanocrystalline diamond thin-film elec-
trodes deposited at 0.50 and 1.25 mA/cm2. The scans were initiated
at 200 mV with the forward sweep in the positive direction at a rate
Figure 4. Cyclic voltammetric i-E curves in 0.1 M HClO4 for Pt/BMD
electrodes deposited with Pt at the different current densities. Pulse number
10. Pulse width 1 s. Scan rate 50 mV/s. The current is normalized to the
BMD geometric area, 0.2 cm2.
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
E189
of 50 mV/s. Again, all the voltammetric features characteristic of
clean polycrystalline Pt are present. There is an increase in the total
voltammetric current as the deposition current density is increased
from 0.50 to 1.25 mA/cm2. This is consistent with the SEM data
and results from an increased Pt loading and electrochemically ac-
tive Pt area. It is worth noting that the nanocrystalline diamond
electrode decorated with Pt at 1.25 mA/cm2 shows much larger vol-
tammetric currents than does the microcrystalline diamond electrode
coated at the same current density. This is due to the smaller nomi-
nal particle size and larger particle coverage on the former. Interest-
ingly, the i-E curve for the film coated at 1.25 mA/cm2 exhibits a
pre-peak prior to Pt oxide formation at ca. 700 mV. This pre-peak is
associated with a PtxOH species formed prior to the PtO monolayer
in the plateau of the curve.52,53 This peak may be due to Pt4OH
formation on the ͑100͒-oriented surfaces and/or Pt3OH formation on
the ͑111͒-oriented surfaces.53
The H+ adsorption charge for the 0.50 and 1.25 mA/cm2 films is
0.071 ± 0.010 and 0.25 ± 0.027 mC/cm2, respectively. The electro-
chemically active Pt area for the films is 0.068 ± 0.010 and
0.24 ± 0.031 cm2, respectively. These values result in roughness
factors of 0.34 and 1.2. Calculations, based on AAS measurement
data, revealed approximate Pt loadings of 1.4 and 2.4 ␮g/cm2 for
the 0.50 and 1.25 mA/cm2 deposition currents, respectively. This
translates into specific Pt surface areas of 24 and 50 m2/g Pt, respec-
tively, which are the highest values we have recorded. It appears
from these preliminary studies that the diamond film morphology
and microstructure do indeed influence the nucleation and growth of
Pt, and the highest specific areas are seen for the nanocrystalline
films.
Comparison studies with glassy carbon.—In order to assess
how metal deposition on diamond stacks up against deposition on
sp2 carbon electrodes, we conducted tests with glassy carbon. Based
on the results discussed previously, the following conditions were
selected for Pt deposition: Ten pulses of 1 s duration ͑delay time of
1 s between pulses͒ at 1.25 mA/cm2. SEM was used to evaluate the
metal deposit. Particle size analysis revealed a particle diameter of
67 ± 55 nm ͑RSD = 82%͒ and a particle coverage of 5.3 ͑±1.3͒
ϫ 109 cm−2. Cyclic voltammetry was employed to study the Pt ac-
tivity for H+ adsorption in 0.1 M HClO4. Integration of the i-E
curves revealed an H+ adsorption charge of 0.25 ± 0.018 mC/cm2
͑n = 3͒. This charge is similar to that seen for the nanocrystalline
film and is a little larger than the value for microcrystalline dia-
mond. The electrochemically active Pt area was calculated to be
0.24 ± 0.017 cm2. In summary, the metal phase formation on glassy
carbon under these deposition conditions appears similar to what is
seen for both diamond types in terms of the nominal particle size,
coverage, and electrochemically active Pt area.
Figure 5. SEM images ͑secondary electron͒ of Pt/BND electrodes deposited
at pulse current densities of ͑A͒ 0.50 and ͑B͒ 1.25 mA/cm2, respectively.
Pulse number 10. Pulse width 1 s.
The specific Pt surface areas on diamond were in the range of
10-50 m2/g Pt ͑see Table III͒. These values are about a factor of
2-10 less than that for a typical elecrocatalyst, 100-200 m2/g Pt.
Gloaguen et al. reported values of 15-73 m2/g Pt for adlayers on
three different types of carbon powders.54 It is important to remem-
ber that the specific Pt surface area depends on the surface area of
the carbon support. Kucernak et al. reported values of 20-50 m2/g
Pt for electrodeposited adlayers on highly ordered pyrolytic graphite
͑HOPG͒.55 Mo et al. reported on the immobilization of high-area Pt
particles on glassy carbon with specific surface areas of ca. 30 m2/g
Pt.56 It is clear that the deposition on diamond yields electrocatalyst
structures and activities that are similar to those for other sp2 carbon
support materials.
Secondary diamond growth.—The effect of a secondary dia-
mond growth on the activity and stability of the Pt nanoparticles on
microcrystalline diamond was investigated. A microcrystalline dia-
mond thin-film electrode was coated with Pt using ten 1 s pulses
duration at a current density of 1.25 mA/cm2. The initial H+ adsorp-
tion charge in 0.1 M HClO4 was 0.21 mC/cm2. This corresponds to
an electrochemically active Pt area of 0.20 cm2. SEM images re-
Figure 6. Cyclic voltammetric i-E curves in 0.1 M HClO4 for Pt/BND elec-
trodes deposited at 0.50 and 1.25 mA/cm2. Pulse number 10. Pulse width
1 s. Scan rate 50 mV/s. The current is normalized to the BND geometric
area, 0.2 cm2.
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

E190
Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
duces an increased particle coverage up to the 1.25 mA/cm2 level, at
which point particle coalescence begins to occur. This trend appears
more consistent with nucleation via a progressive mechanism.
Growth of new Pt particles appears to occur on both existing Pt sites
and at sites on the diamond surface. We have previously found,
using EC-AFM and i-t transients, that the nucleation of Cu on mi-
crocrystalline diamond follows an instantaneous mechanism at low
overpotentials ͑␩ Ͻ 500 mV͒ and shifts to a progressive mecha-
nism at higher overpotentials.57 Vinokur et al. studied the elec-
trodeposition of Ag and Hg on diamond using i-t transients and
found that the mechanism of nucleation depended on the overpoten-
tial and the metal ion concentration.32 At low overpotentials, instan-
taneous nucleation was observed and at high overpotentials or metal
ion concentrations the process became progressive. Preliminary re-
sults using EC-AFM and i-t transients have revealed that the elec-
trodeposition of the more electronegative Zn on microcrystalline
diamond follows a more progressive nucleation mechanism at both
low and high overpotentials.57
Finally, it is useful to consider what challenges there are to elec-
trochemically producing a dimensionally uniform metal adlayer on
polycrystalline diamond. The physical aspects of the deposition
method certainly will impact the dimensional uniformity of the
metal deposits, as does the heterogeneity of the electrode’s micro-
structural and electronic properties. Electrically conducting diamond
is a quite heterogeneous electrode material, both microstructurally
and electronically. The polycrystalline films possess diamond crys-
tallites or grains, grain boundaries, and a multitude of other defects
͑e.g., dislocations, step edges, etc.͒. The microcrystalline films are
rough with valleys between the crystallites that could serve as higher
coordination sites for metal phase formation, whereas the nanocrys-
talline films are smooth but possess a high fraction of exposed grain
boundary due to the small crystallite size. We suppose that the grain
boundaries are the primary nucleation sites initially and, therefore,
the high grain boundary density leads to a smaller nominal particle
size and larger particle coverage.
The electronic properties of diamond also play a key role on the
dispersion and uniformity of metal adlayers. The electronic proper-
ties of diamond are controlled in a complex manner by ͑i͒ the boron
doping level and distribution throughout the film,58-63 ͑ii͒ incorpo-
rated hydrogen which can act both as an acceptor and provide a
charge carrier or as a donor and passivate a boron acceptor,64-68 and
͑iii͒ defect density.63,69,70 Of these, the boron doping level and dis-
tribution are probably the most influential. Furthermore, it is known
that boron incorporates into polycrystalline diamond with different
concentrations depending on the growth sector.71,72 The boron con-
centration in the ͕111͖ growth sector is five or more times greater
than that found in the ͕100͖ sector. In other words, polycrystalline
diamond, particularly the microcrystalline films, is composed of
sites of faster ͑reversible͒ kinetics where the dopant level is high and
sites of slower kinetics ͑less reversible͒ where there is less dopant.
We have recently observed such electrical and electrochemical het-
erogeneity using CP-AFM mapping and scanning electrochemical
microscopy ͑SECM͒ of microcrystalline diamond films.73 Similar
heterogeneity is seen for the nanocrystalline films as well. An ex-
ample of this is shown in Fig. 7a-d. Both height mode images and
conductivity maps are presented over a 10 ϫ 10 ͑A͒ and 1
ϫ 1 ␮m ͑C͒ area. Nodular features are seen in the images with a
size of 100-500 nm. These nodular features are actually clusters of
diamond grains that are 10-15 nm in diameter.26,27 The intersection
of the clusters constitute the grain boundaries. The figure also shows
conductivity maps over the same areas ͑B and D͒. In these measure-
ments, a Au-coated Si tip contacting the surface was rastered over an
area and the current was measured using a bias voltage of +2 V
͑Etip-Esubstrate͒. The bright areas correspond to regions of higher con-
ductivity and the darker features to regions of lower conductivity.
Clearly, there are conductivity variations across the surface. The
more conductive regions do not appear to be exclusively at the grain
boundaries. The higher resolution image in Fig. 7d reveals that the
distance between the conducting regions is on the order of 200
vealed good metal coverage over the entire diamond surface. A
nominal particle size of 25 ± 31 nm and particle coverage of 6.3
ϫ 109 cm−2 were determined from particle size analysis. No loss of
Pt activity was observed after long-term solution exposure.
The metal-coated film was then subjected to a 30 min diamond
deposition using a 0.5% CH4/H2 source gas mixture at 1 kW,
200 sccm of total gas flow, 40 Torr, and ca. 800°C. These condi-
tions are not necessarily optimum but rather were selected as a start-
ing point. A nominal particle size of 44 ± 37 nm and particle cov-
erage of 4.0 ϫ 109 cm−2 were determined from SEM images. The
slightly larger nominal particle size and lower particle coverage are
consistent with some coalescence of neighboring particles as the
deposition temperature is ca. 800°C. More importantly, the particle
shape changed from a rough, dendritic morphology to a smoother,
more rounded morphology during the plasma treatment as a result of
annealing effects.
After the secondary diamond growth, background cyclic voltam-
metric i-E curves were re-recorded in 0.1 M HClO4. The H+ adsorp-
tion charge decreased to 0.015 mC/cm2 ͑a factor of 10 loss͒, and
this corresponds to a decreased electrochemically active Pt area of
0.014 cm2. There is clearly some loss in Pt activity due to particle
coalescence and blockage by the diamond deposition. However, we
suspect that a sizeable percentage of the loss seen here resulted not
from “buried” particles but rather from poor alignment of the met-
allized electrode area inside the O-ring of the cell. The Pt exposed to
the solution was anchored strongly and was extremely stable during
an extended potential cycling period ͑1000 cycles͒ between −0.4
and 1.9 V vs. Ag/AgCl in 0.1 M HClO4. The maximum currents
were near ±5 mA/cm2 at the two potential extremes. The H+ ad-
sorption charge actually increased slightly to 0.020 mC/cm2 after
cycling due to removal of carbon contaminants from the surface and
particle roughening. In comparison, over 63% of the electrochemi-
cally active Pt was lost from a metal-coated diamond surface ex-
posed to the same cycling conditions when no secondary diamond
growth was applied. Research is ongoing to optimize the secondary
diamond growth conditions in order to maximize the particle stabil-
ity but minimize the extent of Pt activity loss.
Discussion
The results presented herein demonstrate that pulsed galvano-
static deposition is a useful method for depositing nanometer-sized
particles of Pt on diamond electrode surfaces. In terms of the nomi-
nal particle size, particle coverage, and electrochemically active Pt,
pulsed deposition is superior to constant current deposition.19-21 The
optimum conditions for depositing Pt on both types of diamond
were ten 1 s pulses at 1.25 mA/cm2 with a 1 s delay between each
pulse. The nominal particle size of ca. 25 nm and particle coverage
of ca. 1010 cm−2 seen for the nanocrystalline film are good values
for a supported electrocatalyst. These values are also comparable to
what was achieved with glassy carbon, indicating that metal depo-
sition on diamond occurs in a similar manner to that on an sp2
carbon electrode.
The basic objective of pulsed deposition is to reduce the average
growth rate of particles, which is expected to reduce the interactions
between closely spaced ones. While we did not comprehensively
investigate the nucleation and growth mechanism, there are some
trends in the data that shed light on the mechanistic aspects of the
deposition. The nominal particle size increases and the particle cov-
erage decreases with increasing pulse number at a fixed deposition
current density ͑i.e., constant ␩͒. It appears from our results that the
initial nucleation occurs at a fixed number of sites and that new Pt
particles nucleate and grow on existing Pt rather than forming at
new sites on the diamond surface. This explains the rough, dendritic
morphology of the deposits. With longer pulse times and therefore
more charge passed, the growth of neighboring nuclei becomes
coupled after a sufficient growth time. This results in particle coa-
lescence, a reduced particle coverage, and an increased nominal par-
ticle size.
Increasing the deposition current density ͑i.e., increasing ␩͒ pro-
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
E191
Figure 7. AFM height mode images ͑air͒ of a boron-doped nanocrystalline diamond thin film over ͑A͒ a 10 ϫ 10 and ͑C͒ a 1 ϫ 1 ␮m area. Simultaneously
recorded conductivity maps of the same regions ͑B and D͒ with a bias voltage of +2 V ͑Etip-Esubstrate͒.
mum deposition conditions. The typical specific surface areas were
in the 10-50 m2/g Pt range. The deposition of Pt on diamond com-
pared favorably to deposition on glassy carbon. The microstructure
and morphology of diamond were observed to strongly influence the
nucleation and growth of Pt. The highest specific surface area of
50 m2/g Pt was observed for the nanocrystalline film, which pos-
sesses a high fraction of exposed grain boundaries. The grain bound-
aries appear to serve as the primary nucleation sites on this film.
Finally, the influence of the film’s electronic properties on the metal
phase formation was investigated. The polycrystalline diamond film
is quite heterogeneous in terms of the electrical conductivity, as
evidenced by CP-AFM. The film is composed of sites of faster ͑re-
versible͒ kinetics where the dopant level is high and sites of slower
kinetics ͑less reversible͒ where there is less dopant. It is supposed
that the regions of high electrical conductivity serve as the initial
nucleation sites.
-300 nm in some cases. These data are important and have implica-
tions for the dimensional uniformity of the metal adlayers. The take-
home message is that inherently there is going to be spatial varia-
tions in the metal adlayer formation due to this heterogeneity in
electrical conductivity. It remains to be proven but it is logical to
suppose that the conductive regions are the sites where initial nucle-
ation occurs. Therefore, the fraction of these conductive sites on a
film will control the initial nucleation density. A similar conclusion
was recently reached by Enea et al. in their AFM study of the
electrodeposition of Pt on polycrystalline diamond.33
Conclusions
The pulsed galvanostatic deposition of Pt electrocatalyst particles
on boron-doped microcrystalline and nanocrystalline diamond thin
film was investigated. The deposition was studied as a function of
the pulse number and current density, while maintaining a pulse
length of 1 s and a duty cycle of 50%. Pulsed galvanostatic deposi-
tion produced a nominal particle size that is an order of magnitude
smaller than that previously observed for constant current
deposition.19,20 Deposition using ten pulses and a current density of
1.25 mA/cm2 yielded the most active electrocatalyst on both dia-
mond types, in terms of the nominal particle size, particle coverage,
and the highest specific Pt surface area. For both electrode types, the
nominal particle size was ca. 30 nm with an RSD of 50% or less,
and the particle coverage was ca. 107 to 1010 cm−2 under the opti-
Acknowledgments
This work was sponsored by the U.S. Department of Energy,
Office of Science ͑DE-FG03-95ER14577͒, and the Center for Fun-
damental Materials Research at Michigan State University.
Michigan State University assisted in meeting the publication costs of
this article.
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

E192
Journal of The Electrochemical Society, 152 ͑5͒ E184-E192 ͑2005͒
Nanoparticles, D. L. Feldheim and C. A. Foss, Jr., Editors, p. 237, Marcel Dekker,
Inc. New York ͑2002͒.
References
1. E. Antolini, J. Mater. Sci., 38, 2995 ͑2003͒.
2. F. Rodriguez-Reinoso, Carbon, 36, 159 ͑1998͒.
40. R. M. Penner, J. Phys. Chem. B, 105, 8672 ͑2001͒.
41. R. M. Penner, J. Phys. Chem. B, 106, 3339 ͑2002͒.
42. H. Liu, F. Favier, K. Ng, M. P. Zach, and R. M. Penner, Electrochim. Acta, 47, 671
͑2001͒.
43. H. Liu and R. M. Penner, J. Phys. Chem. B, 104, 9131 ͑2000͒.
44. G. Gunawardena, G. Hills, I. Montenegro, and B. Scharifker, J. Electroanal. Chem.
Interfacial Electrochem., 138, 225 ͑1982͒.
45. P. Allongue and E. Souteyrand, J. Electroanal. Chem. Interfacial Electrochem.,
286, 217 ͑1990͒.
46. M. C. Granger, M. Witek, J. Xu, J. Wang, M. Hupert, A. Hanks, M. D. Koppang,
J. E. Butler, G. Lucazeau, M. Mermoux, J. W. Strojek, and G. M. Swain, Anal.
Chem., 72, 3793 ͑2000͒.
47. S. Ranganathan, T.-C. Kuo, and R. L. McCreery, Anal. Chem., 71, 3574 ͑1999͒.
48. J. Perez, A. A. Tanaka, E. R. Gonzalez, and E. A. Ticianelli, J. Electrochem. Soc.,
141, 431 ͑1994͒.
49. J. M. D. Rodíguez, J. A. H. Melián, and J. P. Peña, J. Chem. Educ., 77, 1195
͑2000͒.
3. L. Carrette, K. A. Friedrich, and U. Stimming, Fuel Cells, 1, 5 ͑2001͒.
4. J. Y. Lucisano, J. C. Armour, and D. A. Gough, Anal. Chem., 59, 736 ͑1987͒.
5. A. Damjanovic and V. Brusic, Electrochim. Acta, 12, 615 ͑1967͒.
6. N. Giordano, E. Passalacqua, L. Pino, A. S. Aricó, V. Antonucci, M. Vivaldi, and
K. Kinoshita, Electrochim. Acta, 36, 1979 ͑1991͒.
7. N. M. Markovic, T. J. Schmidt, V. Stamenkovic, and P. N. Ross, Fuel Cells, 1, 105
͑2001͒.
8. H.-H. Yang and R. L. McCreery, J. Electrochem. Soc., 147, 3420 ͑2000͒.
9. T. Yano, E. Popa, D. A. Tryk, K. Hashimoto, and A. Fujishima, J. Electrochem.
Soc., 146, 1081 ͑1999͒.
10. E. Yeager, Electrochim. Acta, 29, 1527 ͑1984͒.
11. I. Morcos and E. Yeager, Electrochim. Acta, 15, 953 ͑1970͒.
12. E. Yeager, J. A. Molla, and S. Gupta, in Electrochemistry of Carbon, S. Saranga-
pani, J. R. Akridge, and B. Schumm, Editors, PV 84-5, p. 123, The Electrochemical
Society Proceedings Series, Pennington, NJ ͑1984͒.
13. E. Yeager and D. Tryk, in Proceedings of the 33rd International Power Sources
Symposium, Cherry Hill, NJ, June 13-16, 1988, The Electrochemical Society, Inc.
͑1988͒.
50. A. Essalik, K. Amouzegar, and O. Savadogo, J. Appl. Electrochem., 25, 404
͑1995͒.
14. B. C. H. Steele and A. Heinzel, Nature (London), 414, 345 ͑2001͒.
15. E. Auer, A. Freund, J. Pietsch, and T. Tacke, Appl. Catal., A, 173, 259 ͑1998͒.
16. A. J. Appleby, Corrosion (Houston), 43, 398 ͑1987͒.
17. R. Makharia, P. Yu, J. Pisco, S. Kocha, and H. Gasteiger, Paper 1888 presented at
The Electrochemical Society Meeting, Honolulu, HI, Oct 3-8, 2004.
18. J. Wang, G. M. Swain, T. Tachibana, and K. Kobashi, Electrochem. Solid-State
Lett., 3, 286 ͑2000͒.
19. J. Wang and G. M. Swain, Electrochem. Solid-State Lett., 5, E4 ͑2002͒.
20. J. Wang and G. M. Swain, J. Electrochem. Soc., 150, E24 ͑2003͒.
21. M. Hupert, A. Muck, J. Wang, J. Stotter, Z. Cvackova, S. Haymond, Y. Show, and
G. M. Swain, Diamond Relat. Mater., 12, 1940 ͑2003͒.
22. G. M. Swain, J. Electrochem. Soc., 141, 3382 ͑1994͒.
23. J. Xu, M. C. Granger, Q. Chen, J. W. Strojek, T. E. Lister, and G. M. Swain, Anal.
Chem., 69, 591A ͑1997͒.
24. M. C. Granger, J. Xu, J. W. Strojek, and G. M. Swain, Anal. Chim. Acta, 397, 145
͑1999͒.
25. G. M. Swain, A. B. Anderson, and J. C. Angus, MRS Bull., 23, 56 ͑1998͒.
26. Q. Chen, D. M. Gruen, A. R. Krauss, T. D. Corrigan, M. Witek, and G. M. Swain,
J. Electrochem. Soc., 148, E44 ͑2001͒.
27. Y. Show, M. A. Witek, P. Sonthalia, and G. M. Swain, Chem. Mater., 15, 879
͑2003͒.
28. A. E. Fischer, Y. Show, and G. M. Swain, Anal. Chem., 76, 2553 ͑2004͒.
29. M. Awada, J. W. Strojek, and G. M. Swain, J. Electrochem. Soc., 142, L42 ͑1995͒.
30. Y. Zhang, S. Asahina, S. Yoshihara, and T. Shirakashi, Electrochim. Acta, 48, 741
͑2003͒.
31. S. Nakabayashi, D. A. Tryk, A. Fujishima, and N. Ohta, Chem. Phys. Lett., 300,
409 ͑1999͒.
51. P. Sonthalia, E. McGaw, Y. Show, and G. M. Swain, Anal. Chim. Acta, 522, 35
͑2004͒.
52. H. Angerstein-Kozlowska, B. E. Conway, and W. B. A. Sharp, J. Electroanal.
Chem. Interfacial Electrochem., 43, 9 ͑1973͒.
53. B. V. Tilak, B. E. Conway, and H. Angerstein-Kozlowska, J. Electroanal. Chem.
Interfacial Electrochem., 48, 1 ͑1973͒.
54. F. Gloaguen, J.-M. Leger, and C. Lamy, J. Appl. Electrochem., 27, 1052 ͑1997͒.
55. A. R. Kucernak, P. B. Chowdhury, C. P. Wilde, G. H. Kelsall, Y. Y. Zhu, and D. E.
Williams, Electrochim. Acta, 45, 4483 ͑2000͒.
56. Y. Mo, S. Sarangapani, A. Le, and D. A. Scherson, J. Electroanal. Chem., 528, 35
͑2002͒.
57. J. Wang, Ph.D. Dissertation, Michigan State University, East Lansing, MI ͑2002͒.
58. J. T. Huang, C. S. Hu, J. Hwang, H. Chang, and L. J. Lee, Appl. Phys. Lett., 67,
2382 ͑1995͒.
59. K. Nishimura, K. Das, and J. T. Glass, J. Appl. Phys., 69, 3142 ͑1991͒.
60. N. Vinokur, B. Miller, Y. Avyigal, and R. Kalish, J. Electrochem. Soc., 143, L238
͑1996͒.
61. M. N. Latto, G. Pastor-Moreno, and D. J. Riley, Electroanalysis, 16, 434 ͑2004͒.
62. R. F. Mamin and T. Inushima, Phys. Rev. B, 63, 033201 ͑2001͒.
63. W. Zhu, in Diamond: Electronic Properties and Applications, L. S. Pan and D. R.
Kania, Editors, Chap. 5, Kluwer Academic Publishers, Boston, MA ͑1995͒.
64. M. I. Landstrass and K. V. Ravi, Appl. Phys. Lett., 55, 1391 ͑1989͒.
65. K. Hayashi, S. Yamanaka, H. Okushi, and K. Kajimura, Appl. Phys. Lett., 68, 376
͑1996͒.
66. H. J. Looi, R. B. Jackman, and J. S. Foord, Appl. Phys. Lett., 72, 353 ͑1998͒.
67. H. J. Looi, L. Y. S. Pang, A. B. Molloy, F. Jones, J. S. Foord, and R. B. Jackman,
Diamond Relat. Mater., 7, 550 ͑1998͒.
68. H. J. Looi, M. D. Whitfield, J. S. Foord, and R. B. Jackman, Thin Solid Films,
343-344, 623 ͑1999͒.
69. B. Fiegl, R. Kuhnert, M. Ben-Chorin, and F. Koch, Appl. Phys. Lett., 65, 371
͑1994͒.
70. D. Stenbach, A. Flöter, H. Güttler, R. Zachai, and P. Ziemann, Diamond Relat.
Mater., 8, 273 ͑1999͒.
32. N. Vinokur, B. Miller, Y. Avyigal, and R. Kalish, J. Electrochem. Soc., 146, 125
͑1999͒.
33. O. Enea, B. Riedo, and G. Dietler, Nano Lett., 2, 241 ͑2002͒.
34. E. Budevski, G. Staikov, and W. J. Lorenz, in Electrochemical Phase Formation
and Growth, VCH, New York ͑1996͒.
35. M.-S. Löffler, B. Groß, H. Natter, R. Hempelmann, T. Krajewski, and J. Divisek,
Phys. Chem. Chem. Phys., 3, 333 ͑2001͒.
36. J. V. Zoval, R. M. Stiger, P. R. Biernacki, and R. M. Penner, J. Phys. Chem., 100,
837 ͑1996͒.
71. T. Kolber, K. Piplits, R. Haubner, and H. Hutter, Fresenius’ J. Anal. Chem., 365,
636 ͑1999͒.
72. K. Ushizawa, K. Watanabe, T. Ando, I. Sakaguchi, M. Nishitani-Gamo, Y. Sato,
and H. Kanada, Diamond Relat. Mater., 7, 1719 ͑1998͒.
73. K. B. Holt, A. J. Bard, Y. Show, and G. M. Swain, J. Phys. Chem. B, 108, 15117
͑2004͒.
37. J. V. Zoval, J. Lee, S. Gorer, and R. M. Penner, J. Phys. Chem. B, 102, 1166
͑1998͒.
38. J. L. Fransaer and R. M. Penner, J. Phys. Chem. B, 103, 7643 ͑1999͒.
39. S. Gorer, H. Liu, R. M. Stiger, M. P. Zach, J. V. Zoval, and R. M. Penner, in Metal
Downloaded on 2014-11-05 to IP 128.114.34.22 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).