Development of Thin Film Membrane Assemblies with Novel ... · Assemblies with Novel Nanostructured Electrocatalyst for Next Generation ... Nanostructuredmaterials ... Assemblies

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