2015 DOE Hydrogen and Fuel Cells Program Review
Nanosegregated Cathode Catalysts with Ultra-Low Platinum Loading
Nenad M. MarkovicVojislav R. Stamenkovic
Materials Science Division
Argonne National Laboratory
Project ID#FC008
This presentation does not contain any proprietary, confidential, or otherwise restricted information
PIs:
Timeline
• Project end: 9/2015
Budget
• Total Project funding $ 5.1M
Overview
• Project start: 9/2009
Barriers
~ 30-40% (!!!)Cathode kinetics
1) Durability of fuel cell stack
2) Cost (catalyst, membrane, gdl)
3) Performance (losses and activity)
Partners:• Oak Ridge National Laboratory – Karren More
Project Lead:
• Argonne National Laboratory – Debbie Myers
2
• Funding for FY14: $ 764K
• Planned FY15 DOE Funding: $764K
• Los Alamos National Laboratory – Rod Borup
• Argonne National Laboratory
DOE Technical Targets
• Durability w/cycling (80oC): 5000 hrs
• Cost*: $ 30/kWe
• Mass activity @0.9V: 0.44 A/mgPt
• PGM Total content: 0.2 g/kW
• Specific activity @0.9ViR-free: 720 µA/cm2
• Electrochemical area loss: < 40%
• Catalyst support loss: < 30%
• PGM Total loading: 0.2 mg/cm2electrode
*based on Pt cost of $450/troy ounce
Objectives The main focus of ongoing DOE Hydrogen & Fuel Cell Program is developmentof highly-efficient and durable multimetallic PtMN (M, N = Co, Ni, Fe, V, T) nanosegregatedcatalysts for the oxygen reduction reaction with ultra low-Pt content
Relevance
ANL Technical Targets
• Mass activity @ 0.9ViR-free2015 DOE target x 3
• PGM Total content< 0.1g/kW
• Specific activity @ 0.9ViR-free2015 DOE target x 3
• Electrochemical area loss2015 DOE target
3
Materials-by-design approach - by ANL to design, characterize, understand, synthesize/fabricate, test and develope advanced nanosegregated multi-metallic nanoparticles and nanostructured thin metal films
Nanosegregated Profile
Pt3Ni(111)-Skin ~100 times more active than the state-of-the-art Pt/C catalysts
Well-Defined Systems
d-band center [eV]2.63.03.4
Spec
ific
Act
ivity
: ik @
0.9
V [m
A/c
m2 re
al]
0
1
2
3
4
5
Pt3TiPt3V
Pt3Fe
Pt3CoPt3Ni
Pt-polyPt-skin surfacesPt-skeleton surfaces
Act
ivity
impr
ovem
ent f
acto
r vs
. Pt-p
oly
1
2
3
17
18
19
Target Activity Pt3Ni(111)
(a)
Pt/C ---
4
1st Layer
2nd Layer
3rd Layer
4th Layer
Pt=100 at.%
Pt=48 at.%
Ni=52 at.%
Pt=87 at.%
Ni=13 at.%
Pt=75 at.%Ni=25 at.%
Pt[111]-Skin surface
Advanced Nanoscale
Catalyst
Intrinsic Activity
0.6 0.7 0.8 0.9 1.0
-1.5
-1.0
-0.5
0.0
6 nm Pt/C acid leached PtNi/C acid leached/annealed PtNi/C
I (m
A)
E (V vs. RHE)
0.95 V
20-60°C20 mV/s
0.1 M HClO4
RDE:- ORR activity measured at 0.95V- iR corrected currents- Measurements without ionomer
NANOPARTICLESTHIN METAL FILMS / MODEL NANOPARTICLESEXTENDED Multi-M SURFACES
ApproachB
Pt thin film AnnealedPt (111)
I (µA
)
0.2 E (V)0.4 0.6 0.8
-20
0
20
5 nm
A
-20
0
20
Pt thin film SputteredPt (111)
0.2 E (V)0.4 0.6 0.8
I (µA
)
• Activity boost by lower surface coverage of spectators
• Prevent loss of TM atoms without activity decrease
• Rational synthesis based on well-defined systems
• Addition of the elements that hinder Pt dissolution
Approach / Milestone
1.1 Resolved electronic/atomic structure and segregation profile (100%)1.2 Confirmed reaction mechanism of the ORR (100%)
2.1 Physical methods: TM films (5-10 layers), nanoparticles (5-300 nm) (95%)2.2 Established chemical methods: colloidal and impregnation synthesis (95%)
1.3 Improved specific and mass activity (95%)
2.3 Characterization: Ex-situ (UHV, TEM) and in-situ (EXAFS, EC) (100%)2.4 Theoretical modeling (DFT, MC) methods (95%)
Milestone 1. Fundamental understanding (FY09-13) (Accomplished)
Milestone 2. Synthesis and characterization (FY10-14)
(Go-No Go Decision Met)
3.3 MEA testing (50 cm2) of the optimized catalysts (85%)
3.1 New PtM1M2 catalysts with higher activity and improved durability (95%)3.2 Carbon support vs. nanostructured thin film catalysts (95%)
3.4 Scale up of the catalyst fabrication in lab environment (80%)
Milestone 3. Fabrication and testing (FY11-14)
5
Technical Accomplishments FY09 -14: Pt-alloy Nanocatalysts
6
Colloidal solvo - thermal approach has been developed for monodispersed PtMN NPs with controlled size and composition
1o Particle size effect applies to Pt-bimetallic NPs Specific Activity increases withparticle size: 3 < 4.5 < 6 < 9nmMass Activity decreases with particle size Optimal size particle size ~5nm
Efficient surfactant removal methoddoes not change the catalyst properties
2o Temperature induced segregation in Pt-bimetallic NPs Agglomeration prevented
Optimized annealing temperature 400-500oC
(b)
3o Surface chemistry of homogeneous Pt-bimetallic NPs PtxM(1-x) NPs
Dissolution of non Pt surface atoms leads to Pt-skeleton formation
4o Composition effect in Pt-bimetallic NPs Pt3M
Optimal composition of Pt-bimetallic NPs is PtM1 nm
0.22 nm
1 nm1 nm
PtM PtM2 PtM3
J. Phys. Chem. C., 113 (2009) 19365
Phys.Chem.Chem.Phys., 12 (2010) 6933
Adv. Funct. Mat., 21 (2011) 147
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
7
5o Pt-bimetallic catalysts with mutilayered Pt-skin surfaces
1 nm 1 nm
Ni
Position (nm)43 5210
Inte
nsity
(a. u
.)
Pt
Inte
nsity
(a. u
.)
Position (nm)43 5210
Multilayered Pt-skinsurfaces confirmed for PtNi annealed NPs
3-4ML of Pt-skeletonsurfaces for PtNi acid leached NPs
Synthesized PtNi NPs have homogeneous distribution of Pt, Ni
RDE after 4K cycles @60oC (0.6-1.05V vs. RHE): 8-fold specific and 10-fold mass activity improvements over Pt/C
0.0
0.2
0.4
0.6
0.8
1.0 before
Spec
ific
Activ
ity (m
A/cm
2 )
after
0
2
4
6
Impr
ovem
ent F
acto
r(v
s. P
t/C)
0
2
4
6
8
10
afterbefore after0
100
200
300
400
Impr
ovem
ent F
acto
r(v
s. P
t/C)
Mas
s Ac
tivity
( A/g
) before after
0
2
4
6
before0
4
8
10
14
6o Multimetallic NPs can further improve activity and durability Au core
PtFe shell Pt/C Au/PtFe
before beforeAfter 60K cycles After 60K cycles
Pt3FeCo/C Co Kα
Pt LαPt Fe Co
Fe Kα
Highly homogeneous nanoparticles
Additional gain in mass and specific activities vs. Pt and Pt3M alloys
Impr
ovem
ent f
acto
r vs.
Pt
1
2
3
4
5
Mas
s ac
tivity
A/ m
g Pt
0.20
0.10
0.30
0.35
Pt/C Pt3FeCo/C Pt3CoNi/C Pt3FeNi/C
/ C
PtMNTernary NPs
HSAcarbon
Pt3FeCo/C
Pt3CoNi/C
Pt3FeNi/C
JACS, 133 (2011) 14396
Nano Letters, 11 (2011) 919
J. Phys. Chem. Letters, 3 (2012) 1668
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
8
7o Electrochemically active surface area of Pt-Skin catalystsTEM
Pt-NPs PtNi-NPs
davg = 5 nm
Pt-Skeleton NPs
Pt-Skin NPs
Catalysts with multilayered Pt-skin surfaces exhibit substantially lower coverage by Hupd vs. Pt/C
(up to 40% lower Hupd region is obtained on Pt-Skin catalyst)
Surface coverage of adsorbed CO is not affected on Pt-skin surfaces
Ratio between QCO/QHupd>1 is indication of Pt-skin formation
Electrochemical oxidation of adsorbed CO should be used for estimation of EAS of Pt-skin catalysts
Benefits: to avoid overestimation of specific activity
8o Multimetallic Pt3NM alloys can further improve activity
0.0
0.5
1.0
1.5
2.0Pt-skeletonPt-skin
Pt3Co
Impr
ovem
ent F
acto
rsvs
. Pt-p
oly
Pt3CoN
i
Pt3FeN
i
Pt3FeC
o
Spec
ific
Activ
ity (m
A/cm
2 )
Pt-poly
0
1
2
3
4
0.0 0.3 0.4
0
1
2
Pt3FePt3(FeCo)1
Pt3CoPt3(CoNi)1
Pt3(FeNi)1
Pt3Ni
ln(j/j Pt
)
P
Pt
Similarly to Pt3M alloys, ternary alloys form Pt-skeleton and Pt-skin surfaces depending on the surface treatment
The most active alloy is Pt3NiCo, with 4-fold improvement factor in specific activity compared to Pt-poly
9o MEA: PtNi-MLSkin/NPs 20,000 potential cycles, 0.6 – 0.95 V
No change in Ni and Pt edges after 20K cycles confirms high stability pf multilayered Pt-Skin under operating conditions
Specific surface area loss was only 12%, while Pt/C catalysts suffer loss of 20-50%
JACS 133 (2011) 14396
J. Phys. Chem. Letters, 3 (2012) 1668
Unpublished
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
9
10o Mesostructured Thin Films with Tunable Morphology
A
-20
0
20
Pt thin film SputteredPt (111)
0.2 E (V)0.4 0.6 0.8
I (µA
)
BPt thin film AnnealedPt (111)
I (µA
)0.2 E (V)0.4 0.6 0.8
-20
0
20
5 nm
0
2
4
6
8
4
8
12
16
20
C
As-deposited
Annealed
Spec
ific
Activ
ity (m
A cm
-2Pt
)
Pt thin film on GC PtNi thin film on GC
Pt3Ni(111)-Skin
ΔT
ΔT
orderingPt Poly
Polycrystalline → (111)
Impr
ovem
ent f
acto
r vs.
Pt-
poly
0
2
4
6
8
4
8
12
16
20 Scientific AchievementControl of surface structure and morphology of multimetallic thin films without use of templates for epitaxial growth
Significance and ImpactEnables electrocatalyticproperties of Pt-alloy single crystals in thin film materials
NanoStructuredThin Films 20 nm
1o
A
x10
Surface Modification
andSubstrate Evaporation
20 nm
2o
B
x10
2 nm B’
2 nmA’
MesostructuredThin Films
20 nm
3o
C
x10
2 nmC’
Nano Structured
Meso Structured
-0.8
-0.4
0.0
0.4
0.0 0.2 0.4 0.6 0.8 1.0 1.2
E (V vs RHE)
I (m
A cm
-2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
-1.5
-1.0
-0.5
0.0
I (m
A)
E (V vs RHE)
0.6
1.2
1.8
2.4
2
4
6
8
0.90
0.95
1.00
0.01 0.1 1ikin (mA cm-2)
E (V
vs
RHE)
c
d ΔT
PtNi NSTF
Impr
ovem
ent F
acto
r vs.
Pt P
oly
i kin
(mA
cm
Pt-2
)
Pt NSTF
Pt Poly
Pt/C PtNi Meso-TF
PtNi Meso-TFPtNi NSTFPt NSTFPt/C
2 3
@0.95V vs. RHE
Nature Materials, 11 (2012) 1051
MSTF vs. Pt/C:SA 20-fold MA 6-fold
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
10
11o Highly active and durable multimetallic NWs
Co32Pt68 Co12Pt88
)highly crystalline
segregation profiles
CV/ORR Stability Test:4,000 cycles0.6-1.0V0.1M HClO4
Pt Alloy NWs are active and durable catalyst with no change in activity after 4,000 cyclesSpecific activity depends on the composition and width of NWsAnnealing of NWs induces formation of nanosegregated profile with Pt-Skin type of surfacePt-Skin confirmed by suppressed Hupd, Pt-OH shift, COad/Hupd ratio, and high ORR activity
12o Core-Shell particles with Au interlayer
Ni
AuPt
4nm~ 5-6nm
20nm
- Pt - Au
segregation trend of Au onto surfacedriving force that diffuses Pt into the bulkdriving force induced by strong Pt - OHad interaction
- O
segregation trend of Pt into the bulk
- Fe- Ni
Nano Letters, 14 (2014) 6361
Angew. Chem. Int.Ed., 52 (2013) 3465width 5.5 nm
11
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
Scientific AchievementNanoparticles with tuned size, surface and subsurface compositional profile based onNi core coated with Au interlayer which is covered by PtNi shell enable advanced electrocatlytic properties for the ORR
Significance and ImpactORR specific and mass activities of NP withcore/interlayer/shell are 8-fold more active than Pt/C catalyst after less than 10% of loss in activity in 10K cycles between 0.6 and 1.1V
Research Details–Monodisperse 3nm Ni NPs were synthesized as core–Thickness of the Au interlayer was tuned for durability–Threshold content of Au was found to be 5 at. %–PtNi shell was deposited over Ni/Au core/shell particles–Synergy between electronic effect and Au surface energy defines advanced electrocatalytic properties
Nano Letters 14 (2014) 6361-6367
Pt/C
PtNi/C
Ni/Au/NiPt/C
- Pt - Au
- O
- Fe- Ni
Au content (at. %)Re
tain
ed a
ctiv
ity (
%)
Non-PGM core /Au interlayer/PtM shell
12
Non-PGM core /Au interlayer/PtM shell
- Pt - Au
segregation trend of Au onto surfacedriving force that diffuses Pt into the bulkdriving force induced by strong Pt - OHad interaction
- O
segregation trend of Pt into the bulk
- Fe- Ni
Stabilization mechanism
RDE: 0.6 – 1.1V vs. RHE0.1M HClO41600 rpm
Technical Accomplishments FY09-14: Pt-alloy Nanocatalysts
13
Subsurface Au decreases total number of Pt active sites for adsorption of O2
Au core / PtNi shell NPs have the same catalytic activity as PtNi NPs
Subsurface Au does not alter catalytic properties of NPs
4nm
~ 5-6nm
non-PGM core / Au interlayer / PtNi shell
Synthesis, Structural and Electrochemical evaluation of core shell NPsAccomplishments and Progress: Core/Shell NPs with Au interlayer
∆
X∆Pt-Skin
high activity Pt3M
high durability
underlayered Au
14
Synthesis, Structural and Electrochemical evaluation of core shell NPsAccomplishments and Progress: Core/Shell NPs with Au interlayer
Subsurface Au segregates over Pt after thermal annealing which diminish number of Pt active sites for adsorption of O2
15
Synthesis, Structural and Electrochemical evaluation of core shell NPsAccomplishments and Progress: Core/Shell NPs with Au interlayer
Subsurface Au does not segregate over Pt after thermal annealing, preserves number of Pt active sites and forms Pt-Skin overlayer with high ORR activity
0
2
4
6
8
4
8
12
16
20
C
As-deposited
Annealed
Spec
ific
Activ
ity (m
A cm
-2Pt
)
Pt thin film on GC PtNi thin film on GC
Pt3Ni(111)-Skin
ΔT
ΔT
orderingPt Poly
Polycrystalline → (111)
Impr
ovem
ent f
acto
r vs.
Pt-
poly
0
2
4
6
8
4
8
12
16
20
Pt PtNi-Skeleton
PtNi-Skin
A
-20
0
20
Pt thin film SputteredPt (111)
0.2 E (V)0.4 0.6 0.8
I (µA
)
BPt thin film AnnealedPt (111)
I (µA
)
0.2 E (V)0.4 0.6 0.8
-20
0
20
5 nm
Dissolution of Pt surface and Ni near-surface is diminished by 2-3 order of magnitude
16
- H2PtCl6 and Ni(NO3)2 react in oleylamine at 270oC for 3 min forming solid PtNi3 polyhedral NPs- Reacting solution is exposed to O2 that induces spontaneous corrosion of Ni
- Ni rich NPs are converted into Pt3Ni nanoframes with Pt-skeleton type of surfaces
- Controlled annealing induces Pt-Skin formation on nanoframe surfaces
Synthesis, Structural and Electrochemical evaluation of Nanoframes
Science , 343 (2014) 1339
Technical Accomplishments FY14: PtNi Nanoframes
17
C
Incorporation of Ionic Liquid Into the Nanoframes
- No change in activity after 10K cycles 0.6 – 1.0 V
- Mass activity increase over 35-fold vs. Pt/C
- Specific activity increase over 20-fold vs. Pt/C
- Increase in mass activity over 15-fold vs. DOE target
Science , 343 (2014) 1339
RDE @ 0.95V vs. RHE0.1M HClO41600 rpm
RDE @ 0.90V vs. RHE0.1M HClO41600 rpm
Technical Accomplishments FY14: PtNi Nanoframes
18
Lab Scale Synthesis, Structural and Electrochemical Evaluations
Accomplishments and Progress: PtNi Nanoframes
Improvement Factor vs. Pt/C
Specific Activity @0.95 V (mA cm-2)
Size
(nm
)
Pt/C PtNi/C
30 mg of Catalysts per batch 60 mg of Catalysts per batch
19
Nanoframes in 5 cm2 MEA ANL and ORNL
Accomplishments and Progress: PtNi Nanoframes
0.1 µm
HAADF-STEM
0.1 µm
BF-STEM
membraneca
taly
st la
yer
membrane
5 nm
BF-STEM Pt Ni
5 nm
20
Nanoframes in RDE with Ionomer and T
Accomplishments and Progress: PtNi Nanoframes
Specific Activity of Pt/C TKK 20 wt% I/C=0.8, 60°C,
0.9 V: 0.2 mA/cm²
2x decrease in specific activity of with addition of ionomer to nanoframes
Nanoframes have >10x higher activity than 20 wt% Pt/C
20°CSpecific Activity
[mA/cm2]No
Ionomer
20°CSpecific Activity
[mA/cm2]I/C = 0.8
60°C Specific Activity
[mA/cm2]No
Ionomer
60°C Specific Activity
[mA/cm2]I/C = 0.8
0.95V 1.25 0.92 0.659 0.372
0.90V 7.35 4.87 4.14 2.16
21
Nanoframes in 5 cm2 MEA ANL and ORNL
Accomplishments and Progress: PtNi Nanoframes
Cathode Loading: 0.035 mg-Pt/cm2, I/C = 0.8H2/O2, 80°C, 150 kPa(abs), 100%RH
ORR Activity @ 0.9 V: Mass Activity Specific ActivityTKK 20 wt%Pt/C: 0.24 A/mg-Pt 0.45 mA/cm2-PtPtNi Nanoframes: 0.76 A/mg-Pt 2.60 mA/cm2-Pt
22
Nanoframes in 5 cm2 MEA ANL and LANL
Accomplishments and Progress: PtNi Nanoframes
Metric Units DOE 2020 Target
PtNi Nanoframe TKK Pt/C
Pt total loading mg-PGM/cm²geo ≤0.125 0.035 0.035
Mass activity A/[email protected]
≥0.44 0.76 0.22
MEA performance mA/cm²geo @ 800 mV ≥300 148 44.3
0 200 400 600 800 1000 1200 1400 16000.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
H2-Air80 OC100 % RH
Cell
Volta
ge (V
)
Current Density (mA/cm2)
TKK Pt/C PtNi Nanoframe/C
0 500 1000 1500 2000 2500 3000 3500 40000.4
0.5
0.6
0.7
0.8
0.9
1.0
IR c
orre
cted
Cel
l Vol
tage
(V)
Current Density (mA/cm2)
TKK Pt/C PtNi Nanoframes/C
H2-O2
80 OC100 % RH
LANL obtained mass activity of 0.3 A/mgPt @ 80oC and 3x higher Pt loading on the cathode in an unoptimized 5cm2 MEA
H2 / O2 Performance H2 / Air
23
4 nm4 nm4 nm
7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene [MTBD]
Incorporation of Ionic Liquid Into the Nanoframes in MEA
Accomplishments and Progress: PtNi Nanoframes
Initial measurements with nanoframesand IL in MEA justifies this approach
Nanoframes with IL exhibit 30% improved activity
2.0
4.0
6.0
8.0
Atomic number (z)
Activ
ity im
prov
emen
t fac
tor v
s. P
t-pol
y
Pt3CoPt3Fe
Pt3VPt3Ti
Pt3Ni
Activ
ity im
prov
emen
t fac
tor v
s. P
t/C
5.0
10
15
20
Polycrystalline Alloys
Pt - Skin
Pt - Skeleton
20.0 70
Single Crystal Alloys
*
Metallic Nanoparticles dispersed in Carbon
*
22 24 26 28 30 78
PtNiNSTF
Pt3Ni(111)
1.0 * *Pt/C
Pt3Ni
* NSTF
Pt3Co Pt
*NSTF NSTFM
esos
cale
orde
ring
*Pt3CoNiNSTF
24
Electrochemical Activity Map for the ORR RDE and MEA
Accomplishments and Progress: ORR on Pt-alloys
PtNi Meso-STFPtNi Nanoframes
PtNi NF in MEA
25
Efficient implantation of fundamental principles to the practical systems in the form of NPs, NWs, and nanoframes with adjustable compositional profile and structure
Electrocatalysts based on nanosegregated Pt alloy NPs, NWs, MSTFs and Nanoframes
Established methodology that is capable to form and determine the nanosegregatedPt-skin surfaces for different classes of electrocatalysts
Established scalable synthetic protocols to produce larger amounts of materials
Evaluation of multimetallic Pt-alloy electrocatalysts
Different classes of materials have been synthesized in the form of NPs, NWs, nanoframes and characterized by TEM, HRSEM, in-situ HRTEM, XRD, RDE, MEA
Specific activity of Pt-alloy vs. Pt/C electrocatalysts can be improved by 20-fold for Nanoframes and MSTF, 10-fold for core/shell NPs and 7-fold for NWs. Mass activities improvements vs. Pt/C are 36-fold for nanoframes, 7-fold for core/shell, 6-fold for MSTF and 4-fold for NWs (RDE in 0.1M HClO4 @ 0.95V vs. RHE)
Stability of Nanoframes, MSTF, core/shell NPs and NWs is superior compared to Pt/C
Two fold power of annealing facilitates the formation of an energetically more favorable surface state rich in (111) facets and distinct oscillatory segregation profilein core/shell NPs, NWs, mesostructured thin films and Nanoframes
Nanoframes are the first nanoscale catalyst with ORR bulk single crystal activity
S u m m a r y
∆T
26
Future Work
• Tailoring of the composition that can improve/optimize durability/performance in Pt-alloys
• Synthesis of tailored low-PGM practical catalysts (Meso-TF | Core/Interayer/Shell | Nanoframes)
FY 2015
FY 2016 (new funding period)
• Characterization Structural and Electrochemical (RDE, MEA, HRTEM)
• Support – Catalyst interactions / Tuning of the performance
• Scaling-up of synthesis to produce gram scale quantities of the most promising catalysts
• Activity/stability evaluation and optimization of MEA protocols at ANL and LANL
• Alternative approaches towards highly active and stable catalysts with low PGM content
• Achieving full lab scale capacity for scaling up of chemical synthesis of nanoframe catalysts
27
Collaborations
• Oak Ridge National Laboratory – HRTEM
SUB-CONTRACTORS
• Argonne National Laboratory – Nanoscale fabrication and DFT (CNM)COLLABORATORS
• Argonne National Laboratory – MEA Testing D. Myers (CSE)
• Los Alamos National Laboratory – MEA Testing R. Borup / T. Rockward
Publications and Presentations
FY09-15
15 Publications36 Presentations
over 1200 Citations3 issued US patents
5 patent applications
28
