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Development of Thin Film Membrane Assemblies with Novel Nanostructured
Electrocatalyst for Next Generation Fuel Cells
Dr. Bala Haran and Dr. Branko N. PopovDepartment of Chemical Engineering,
University of South Carolina, Columbia, SC 29208Tel: (803) 777-7314 Fax: (803) 777-8265
E mail: [email protected] site: http://www.che.sc.edu
The term nano corresponds to 10-9. So one nanometer
corresponds to one billionth of a meter.
Nanotechnology as the name suggests is the study of
materials of nanodimensions
In general study of materials varying in size from 1 to 100
nm
meter m 100 1 mcentimeter cm 10-2 0.01 mmillimeter mm 10-3 0.001 mmicrometer µm 10-6 0.000001 mnanometer nm 10-9 0.000000001 m
What are nanostructured materials??
a broad class of materials, with microstructures modulated in zero to three dimensions on length scales less than 100 nmmaterials with atoms arranged in nanosizedclusters, which become the constituent grains or building blocks of the material
The Scale of Things -- Nanometers and MoreThings Natural Things Manmade
MicroElectroMechanical Devices10 -100 µm wide
Red blood cellsPollen grain
Head of a pin1-2 mm
Quantum corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip
Corral diameter 14 nm
The
Mic
row
orld
0.1 nm
1 nanometer (nm)
0.01 µm10 nm
0.1 µm100 nm
1 micrometer (µm)
0.01 mm10 µm
0.1 mm100 µm
1 millimeter (mm)
1 cm10 mm
10-2 m
10-3 m
10-4 m
10-5 m
10-6 m
10-7 m
10-8 m
10-9 m
10-10 m
Visib
lesp
ectru
m
The
Nan
owor
ld
1,000 nanometers =
1,000,000 nanometers =
Nanotube electrode
Carbon nanotube~2 nm diameter
Nanotube transistor
O O
O
OO
O OO O OO OO
O
S
O
S
O
S
O
S
O
S
O
S
O
S
O
S
PO
O
21st Century Challenge
Combine nanoscale building blocks to make functional devices, e.g., a photosynthetic reaction center with integral semiconductor storage
Ant~ 5 mm
Dust mite200 µm
Fly ash~ 10-20 µm Human hair
~ 10-50 µm wide
Red blood cellswith white cell
~ 2-5 µm
DNA~2-1/2 nm diameter
ATP synthase
~10 nm diameter
Atoms of siliconspacing ~tenths of nm
Classification of NanostructuredMaterials
Based on the structureNanostructured materials vary from zero dimensional atom clusters to three dimensionalequiaxed grain structure.Each class has at least one dimension in the nanometer range
Atom clusters and filaments are defined as zero modulation dimensionalityand can have any aspect ratio from 1 to ∞
R.W. Siegel, Nanophase Materials, Encyclopedia of Applied Physics, vol. 11, VCH Publishers 1994, p 173
Multilayeredmaterials with layer thickness in the nanometer range are classified as one-dimensionally modulated
Layers in the nanometer thickness range consisting ofultrafinegrains are two-dimensionally modulated
The last class is that consisting of three dimensionally modulatedmicrostructures ornanophasematerials
Synthesis of Nanostructured Materials with Superior Corrosion and Electrocatalytic Properties
Synthesis of Nanostructured Materials by Electrochemical Processes
Underpotential Deposition (UPD) of monolayers of Zn, Ni, Bi onto
hard alloys
Novel autocatalytic reduction process for
deposition of amorphous alloys (Ni-P,
Ni-Co-P)
Galvanostatic pulse treatments for deposition
of ternary and quarternary composites based on Zn, Ni, Cd, P
Superior mechanical properties (low rates of
hydrogen permeation and corrosion)
Superior electrocatalytic properties (long cycle life, low
self discharge, high rate capabilities)
Superior corrosion and catalytic
properties
Underpotential Deposition of NanostructuredMonatomic Layers of Zn, Pb and Bi
UPD occurs with a formation of monatomic layers at potentials more noble than the reversible Nernst potential.UPD has been optimized for Zn, Pb and Bi by using the work functions of these metals and the work function of the substrate.The Underpotential shift (E) when the monatomic layers are formed is determined by the difference in work functions in electron volts of both metals.UPD formed monatomic layers of Pb, Zn and Bi on steel surface inhibit corrosion due to lowering of the binding energy of the hydrogen adatoms on Zn, Pb and Bi adsorbates.
Autocatalytic Reduction Process for Deposition of Nanostructured Composites
1 µm
One step processNo external current is used for deposition.High temperature and large concentration of reducing agent (hypophosphite) during encapsulation leads to hydrogen evolution.Evolved hydrogen penetrates the hydride particles in the bath and results in lowering the particle size.
EPMA of cobalt encapsulated LaNi4.27Sn0.24
alloy
Nanosized amorphous layers of Co-P, Ni-P are deposited by controlling the substrate particle size, the concentration of Co++ or Ni++ in the electrolyte and by controlling the deposition rate (pH, temperature and presence of leveling agents).
DC and Pulse Deposition ofNanostructured Multilayers
The particle nucleation rate and the grain size is controlled by the peak cathodic potential, the pulse period and the relaxation period and the duty cycle.Thin films and nanostructured deposits have been deposited by optimizing the duty cycle and the concentration of leveling agents.The film grain size is proportional to the crystal growth rate and inversely proportional to the nucleation rate.Pulse deposition increases the nucleation rate, decreases the crystal growth rate.
1 µm
Nanostructured Zn-Ni-Cd
1 µm
Multiple Layers of Zn-Ni
Development of Thin Film Membrane Assemblies with NovelNanostructured Electrocatalyst for Next Generation Fuel Cells
Develop superior fuel cell electrodes with better utilization of electrocatalyst
Construct membrane electrodes with nanoparticles of carbon and catalyst particles
Catalysts - Pt/Ru/Fe/NiSynthesize mixed alloy catalysts with Pt-Fe-C and Pt-Ni-C
Nanostructures will lead to Better utilization of noble metal and hence low electrode cost
Decrease cathode polarization
Objectives• improve the kinetics of oxygen reduction by modifying the
electronic and short range atomic order around Pt by developing Pt based binary and ternary (Pt-Fe, Pt-Cu, Pt-Fe-Mn etc)nanocluster assemblies,
• improve understanding of catalyst structural and electronic properties on kinetics of electrochemical reactions,
• optimize the structure of the catalyze layer and its interface with the polymer membrane by selective localization ofnanostructured catalyst through electrodeposition, and
• develop a theoretical model, which will explain the processes occurring at the electrolyte/nanostructured electrode interfaces and will help to optimize the performance and activity of the membrane electrode.
Specific Tasks to Accomplish Goals
• Task 1: Chemical Reduction of Pt Binary and Ternary Catalysts on Carbon,
• Task 2: Synthesis of Pt Binary and Ternary Alloys Through Pulse and Pulse Reversal Electrodeposition,
• Task 3: Material Characterization of NanostructuredCatalysts,
• Task 4: Electrochemical Characterization of Thin Film Membrane Assemblies and,
• Task 5: Theoretical Modeling of Membrane Electrode Assembly.
Task 1: Chemical Reduction of Pt Binary and Ternary Catalysts on Carbon
Colloidal Method for Nanomaterial Synthesis
• Previous Accomplishments
– Developed new technology based on colloidal method, for synthesizing RuO2/carbon nano-composite material.
– Increased specific capacitance and utilization of RuO2 by decreasing particle size and dispersing evenly over carbon.
– Improved the power rate at high current discharge.
Electrode Preparation using the Colloidal Method
Preparation of the colloidal solution using RuCl3·xH2O (39.99 wt% Ru) and NaHCO3
Adsorption of the colloidal particles using carbon black
Filtration using a 0.45 µm filtering membrane
Annealing in air
Mixing with 5wt% PTFE
Grounding to a pellet type electrode
Cold pressing with two tantalum grids
TEM image of RuO2·nH2O/carbon composite electrode (40 wt% Ru)
25 nm
SEM images of RuO2.nH2O/carbon composite electrode
3 µm 3 µm
(80 wt% Ru)(60 wt% Ru )
SEM image of RuO2 deposited on carbon particle by sol-gel method (10.6 wt% Ru)
Y. Sato et al. Electrochem. Solid State Lett. 3 (2000) 113
Comparison of Preparation Techniques for Ruo2 /Carbon Composite Electrode
320 oCCrystalline50wt%2 nm330 F/gHeat decomposition
150 oCAmorphous
10 wt%38 nm720 F/gSol-gel method
100 oCAmorphous40 wt%3 nm863 F/gColloidal method
Annealing temperatureStructureRu loading
limitParticle SizeSpecific
capacitance of RuO2
Task 2: Synthesis of Pt Binary and Ternary Alloys Through Pulse and Pulse Reversal
Electrodeposition
• Objective– Reducing cost of electrode by decreasing Pt loading
– Presenting Pt on the surface contacting with polymer electrolyte.
– Decreasing particle size and increasing activity of Pt
Process of Pulse Electrodeposition
−=η
21 exp kkv
=
0
0 lniiDC
DC ηη
++=
=
++
=
1ln
1lnln
0
0
0
0
on
off
DCPC
DCa
on
offaPC
tt
iitt
ii
ηηη
ηηη
• The rate of nuclei formation, v:
• Overpotential of DC deposition
• Overpotential of PC deposition
ip: peak current densityia : average current density
Previous Accomplishments: Effect of Pulse and DCElectrodeposition at Current Density of 50 mA/cm2
Pulse
20 nm
DC
200 nm
Previous Accomplishments: Effect of Particle Size of Pt on the Performance of PEMFC
A
A
BB
Task 3: Material Characterization ofNanostructured Catalysts
• The crystalline structure, particle sizes and unit cell parameters will be determined for all nanostructured materials synthesized in this study.
• The pore structure of the final materials will be characterized via BET surface area and pore volume, pore size distribution, and mercury porosimetry measurements.
• The morphology of the various microstructures in them will be determined using scanning, (SEM) and transmission electron microscopy (TEM).
• Qualititave estimate of the catalyst thickness will be determined using Electron Probe MicroAnalysis (EPMA).
• Using X-ray diffraction data an attempt will be made to estimate the nature and number of phases present in the final deposit.
Task 4: Electrochemical Characterization of Thin Film Membrane Assemblies
Fuel Cell Test Station for Electrochemical Studies
Task 4: Electrochemical Characterization of Thin Film Membrane Assemblies
• Tafel and linear polarization will be done to determine the catalytic activity of the electrodes.
• Electrochemical impedance spectroscopy will be used to determine the structural changes and deterioration behavior of the electrode materials.
• The rate capability and polarization characteristics of thenanostructured catalysts will be studied as a function of crystalline structure, particle size and inter-atomic distance.
• The kinetics of the processes occurring at the electrode-electrolyte interface will be determined by using slow scan voltammetry.
• The power capability of different thin film MEAs will be determined as a function of particle size.
• This study will provide information on the reactivity of the anode and cathode surface and structural changes of the electrode and will provide means for optimization of the chemical composition of the cathode.
Task 5: Theoretical Modeling of Membrane Electrode Assembly
• We plan to develop a theoretical model, which will explain the processes occurring at the electrolyte/nanostructuredhybrid electrode interfaces and will help to optimize the performance and activity of the membrane electrode.
• Using packing theory, the model will account for incorporating nanosized Pt alloy clusters and large carbon particles over Nafion membrane.
• Effects of active carbon content in the electrode, different types of active carbon with various internal and external surface areas, discharging current density, and electrolyte salt concentration on the system’s performance, will be investigated.
Research in Other Areas
Development of Novel Supercapacitors Based on Hybrid Metal-C Nanoparticles
Capacitors deliver frequent pulses of energy in several electronic circuits
Electrochemical capacitors
Carbon based - Double layer
Metal oxide (Ni, Ru, Co, Mn) - Faradaic reactions
Need new devices which bridge gap between double layer and metal oxide capacitors
Development of Novel Supercapacitors Based on Hybrid Metal-C Nanoparticles
Incorporate nano-particles of Metal Oxide on high surface area carbons
AdvantagesMore energy than electrolytic capacitors
Extremely high power density
Lower resistance than metal oxide capacitors
ApplicationsCommunication - cellular phones
Power conversion - converters, power supplies
Pulse power - actuators, air bag detonation
OPTIMIZATION OF THE CATHODE LONG-TERM STABILITY IN MOLTEN CARBONATE FUEL CELLS
Supported by DOE-FETC
OBJECTIVE: To reduce the corrosion of MCFC cathodes and current collectors at high temperature in the melt
APPROACH
Develop novel fuel cell cathodes with better utilization of electrocatalyst and lower corrosion
Construct electrodes with nickel and Co nanoparticles
Novel electrodes and nanostructures will inhibit electrode dissolution and hence enhance operation life of the fuel cell
DEVELOPMENT OF SUPERIOR CARBON ANODES FOR Li-ION BATTERIES
Supported by Sandia National Laboratories
Li Foil CounterElectrode
WorkingElectrode
Li Foil ReferenceElectrode
Separator
Electrolyte (1M LiPF6 in PC:EC:DMC (1:1:3
Current CollectorTeflon Mould
Swagelok™ three electrode cells
OBJECTIVE:
To reduce the irreversible capacity loss and capacity fade seen in carbon anodes
APPROACHAPPROACH
Modify the surface of carbon by incorporating nano-particles of Pd, Ni and Co.
Optimize the metal loading on carbon
Electrochemically characterize the hybrid metal-C particles
)
Experimental☯ Ni-composite graphite development
☯ through surface modification by dispersing nano-sized Ni-composite particles on the graphite
☯ Pd-P alloy deposited from an electroless bath☯ PdCl2, NH4OH, NH4Cl, NaH2PO2 ; pH=9.0, T= 90oC
☯ Various amounts of Pd were deposited on SFG75 graphite☯ 5%, 8%, 10% and 25% Pd by weight
☯ Electrochemical characterization☯ Swagelok three-electrode cell☯ Electrolyte: PC-EC-DMC (ratio of 1:1:3)
☯ Physical characterization - SEM, BET
SEM Images for Bare and NiSEM Images for Bare and Ni--composite Coated KS10composite Coated KS10
(a) bare KS10 (b) 10 wt% Ni-composite KS10
Surface Morphologies of Pd
Dispersed G
raphite
(b) 5 wt%
Pd -G
raphite(a) B
are G
raphite
Initial ChargeInitial Charge--Discharge Profiles for Discharge Profiles for Bare and NiBare and Ni--composite Coated KS10composite Coated KS10
0
1
2
3
4Po
tent
ial (
V vs
.Li/L
i+ )
bare KS103 wt% Ni-composite KS105 wt% Ni-composite KS10
B
A
0 100 200 300 400 500 600 700 800 900 1000 1100Capacity (mAh/g)
SelfSelf--discharge Performances for Bare discharge Performances for Bare and Niand Ni--composite Coated KS10composite Coated KS10
84
86
88
90
92
94
96
98
100
102
0 1 3 10
Storage time (days)
Disc
harg
e ca
paci
ty re
tain
ed (%
)
bare KS10
10 wt% Ni-composite