Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
2006 DOE Annual Review 1
1
Tungsten Cathode Catalyst for PEM Cells
2006 DOE Hydrogen, Fuel Cells Infrastructure Technologies Program Review
Project ID# FCP 40This presentation does not contain any proprietary or confidential information
May 17, 2006
Joel Christian, Robert Mendenhall, Sean Smith, Richard Gingerich, Hans-Joachim Lunk, Tuan Dang
OSRAM SYLVANIA Products Inc.
2006 DOE Annual Review 2
2
Overview
TimelineProject Start: Feb. 1, 2005Project End: July 1, 2006Percent Complete: 90%
BudgetProject: $406,250- DOE Share: $325,000- Contractor: $81,250Funding in ‘05: $283,236
Technical Barriers/Targets
Non-Pt Catalyst Activity• > 130 A/cm³ @ 0.8V
Durability• 5000 hours (cycling)
Cost• < 8 $/kW
PartnersLANL — testing and ink formulation
2006 DOE Annual Review 3
3
Objectives
Perform R&D on tungsten electrocatalysts to improve power output per gram of material from baseline. This includes evaluating current catalyst in cathode application, and optimizing catalyst synthesis to achieve activity improvement towards attaining the DOE technical targets for non-platinum catalysts. Performance evaluation at 250 hours, and over 1000 hours.
The goal of this work is to produce a catalyst with high specific power at a cost significantly lower than platinum.
2006 DOE Annual Review 4
4
Approach
• Employ reduced polytungstates as cathode electrocatalysts
• Seek performance improvements by optimizing:– precursor composition– precursor loading on carbon– ink formulation– activation conditions
• Perform electrochemical tests for performance and lifetime
2006 DOE Annual Review 5
5
Technical Accomplishments
• Established catalysis in rotating disk half-cell• Demonstrated catalyst improvement
– At LANL• comparing 2004 and 2005 materials, W|Pt 5cm² cell• exceeded project milestone by 50% to 0.02 A/cm²
– at 0.24V, during 20 hr life test
– Internal testing• 4-fold improvement to 0.035 A/cm² at 0.24V• demonstrated catalyst life to 3200hrs
2006 DOE Annual Review 6
6
Technical Accomplishments
• Completed work in 5 key tasks:– activation conditions – precursor composition– precursor loading on carbon– ink formulation– analysis
• Composition change provided the increase in cathode performance
2006 DOE Annual Review 7
Activated POM on XC-72
-0.000035
-0.00003
-0.000025
-0.00002
-0.000015
-0.00001
-0.000005
0
0.000005
0.00001
0.000015
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3
Potential (V vs RHE)
Cel
l Cur
rent
(Am
ps)
O2 on day 1H2 on day 1Ar on day 1onset point
Oxygen
1 mV/sec
5 mV/sec
Hydrogen
Argon
Type IV - RDE "C" - 5mm GC disk
7
Tungsten Only Cell — RDE (anode and cathode)
Demonstration of Catalytic Activity
Conditions:0.5 M HClO45 mV/sec2000 RPMCE: Carbon RodRE: SCE (Hg/Ag)WE: Thin film on
Glassy Carbon
2006 DOE Annual Review 8
8
Tungsten Only Cell — RDE
XPS Analysis of RDE Surface
W(IV)
W(VI)
5700
5800
5900
6000
6100
6200
6300
6400
6500
6600
6700
6870727476788082848688
Binding Energy (eV)
N(E
)/E,s
mo1
1
XPS
XPS
Expected Pt Simulation
Pt
Pt
PtO
PtO
PtOads
PtOads
Pt
Pt
PtO2
PtO2
Pt location
XPS Signal
Possible Platinum Species
• platinum undetected• XPS shows reduced W(IV) present
2006 DOE Annual Review 9
9
Project Results – LANL Testing
Activity Improved to 0.078 A/cm²
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08i (cell current in amps/cm²)
V (v
olts
)OSI Type 1 LANL (2004)
OSI Type 2 LANL (2005)
2006 DOE Annual Review 10
10
Project Results – LANL Testing
2004 2005
both tests at 0.24V, 5cm² cell2004 Test: ~0.04 A in cell = 0.008 A/cm²2005 Test: 0.1 A in cell = 0.02 A/cm²This comparison shows an improvement of 2.5x, project milestone was 2x
20 hour life test at 0.24V shows 2.5x improvement to 0.02 A/cm²
OSRAM-SYLVANIA Cathode Catalyst TestingShort Life Test
Anode: 0.20 mgPt/cm2; Cathode: 0.39 mgW/cm2
MEA Cell Area: 5 cm2; Membrane: Nafion 112; Tcell: 80°C; Pressure: 30 psigH2/Air Flow: 160/550 sccm
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 5 10 15 20Time / h
Cur
rent
@ 0
.24
V / A
2006 DOE Annual Review 11
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
Cell Current (A/cm³)
Cel
l Pot
entia
l (V)
11
Project Results – Current Output at 2000 hrs
60°C, H2:Air, without iR correction, test at OSRAM SYLVANIA
Type II Tungsten Catalysttest at OSRAM SYLVANIA
at 2000 hours
Volumetric current density at 0.8V exceeds DOE non-precious status
DOE status
Type II Tungsten Catalyst (LANL Decal method)
Type I Catalyst (LANL)
DOE 2010 target
2006 DOE Annual Review 12
12
Project Results - Life
No Degradation in Cell Performance to 3200 Hours
H2:Air, initially RT then 60°C
0
2
4
6
8
10
12
14
0 500 1000 1500 2000 2500 3000 3500
Hours of operation (hr)
Pow
er (W
/cm
³)
0
5
10
15
20
25
30
35
40
Volu
met
ric C
ell C
urre
nt D
ensi
ty (A
/cm
³)
Poweri at 790mV avg
2006 DOE Annual Review 13
13
Accomplishments – Activation Task
reduced POM
re-arrangement changes geometry
2.5 Å3.3 Å
+ 6 e-
Source: Jeannin, IC 1980 p 2933
W — W W — W
-7
-6
-5
-4
-3
-2
-1
0
1
2
-1.5 -1 -0.5 0 0.5 1
Potential (Volts vs SCE)
Cur
rent
(mA
)
50 mV/sec
Cyclic Voltammogram of Na6[H2W12O40] precursor Reduction Pathway for Metatungstate
Source: Launay, JINC 38, 807 (1976)
2006 DOE Annual Review 14
14
Precursor loading on carbon
Pore Size Distribution of XC-72
•Carbon Analysis:•PZC (isoelectric point)•pore size
•Objective:•optimizing of W loading on C
15
POM has a higher possible site density (SD) than Pt
7.6 (1020sites/cm³)16 (1020sites/cm³)75% Metal Utilization 5% Metal Utilization
Idealized polytungstate and Pt electrode surfaces
Future Work
16
Tungsten catalyst on track to meet the 2010 targets
Mat’l TOF SD SDMAX A/cm³Pt(2) 25 3.2
0.62
4.2
POMMAX 5 16 1300
3.1
7.6(1,4) 1300
W—POM(current)
1.59 16(4) 16
2010 POM 2 136
req’d3 1.6-4 60 - 160
ref 2: Gasteiger et al, Appl Cat B 56 (2005) 9-35
ref 1: Fuel Cell Handbook v2 p 471, citing Kinoshita
ref 4: lecture notes, Jim Benushi, Cabot Corp.
ref 3: Wagner et al, DOE Workshop 3/20/03
6.77x
SD = site density(1020 catalytic sites per cm³)
TOF = turnover frequency(catalytic reactions per second per site)
17
Areas for Improvement
Charge Transfer Kinetics
Active Sites
Stability Enhancement
Redox Tuning
Compositional Changes
(TOF)
(SD)
(TOF, SD)
(TOF, SD)
(TOF, SD)
2006 DOE Annual Review 18
18
Future Work• Project conclusion
– complete data collection– final report by 6/30/06
• Proposed for FY07– Continuing investigation on:
• demonstration of activity (in a Pt-free cell)• optimization of activation step• precursor composition• methods to improve loading/dispersion
• Proposed multi-year program FY07/FY10 – meet 2010 DOE target of 130 A/cm³
2006 DOE Annual Review 19
19
Summary• Catalysis demonstrated on rotated disk electrode
– anode and cathode catalysis• PEM Cell performance demonstrated
– above DOE’s non-precious metal 2004 status– cathode operation to 3200 hours– project milestone exceeded
• Space model shows on-track to 2010 target– plan proposed to achieve 130 A/cm³
2006 DOE Annual Review 20
20
Backup Slides
2006 DOE Annual Review 21
21
Critical Assumptions and Issues• Adventitious Platinum
– Pt could migrate across membrane during• synthesis/activation• operation
– Protocol is needed to assess effect in PEM cell• detection of Pt in non-Pt catalyst area• quantification of Pt in non-Pt catalyst area• performance effect of Pt in non-Pt catalyst area
– Life test MEA assumes no Pt• analysis protocol being developed
2006 DOE Annual Review 22
22
Acid Resistant Elements
2006 DOE Annual Review 23
Polyoxometalate (POM) - Features• Keggin type shown• One central heteroatom• Octahedra of WO6 “poly”atoms• Substituted “poly”atoms
– Poly- W, Mo, V, Nb, Ta– Hetero- 12 – 50 elements possible– Lacunary possible
• Can be extremely soluble• Potential “Designer” material
– Redox properties– High charge– High ionic weight– High charge delocalization
10 Å
2006 DOE Annual Review 24
AMT Properties• Isopolymetalate• Formula: (NH4)6[H2W12O40] • 5H2O• MW = 2958 g/mol (plus ~5 H2O)• Solubility: 2 kg/L • Charge localization: broad• Keggin structure with two H heteroatoms• pH of aqueous solution ~3 6-
25
Acknowledgements:
U. S. Department of EnergyValri Lightner
Nancy Garland
Bob FillnowJeff Dann
Frank VenskytisTim Bard
Tom WolfePaul Sedor
Héctor AbruñaStan Whittingham
Piotr ZelenayTommy RockwardFrancisco Uribe
Mike Hickner