Hybrid Sulfur Thermochemical Process Development
William A. SummersSavannah River National Laboratory
June 12, 2008
This presentation does not contain any proprietary, confidential or otherwise restricted information
DOE Hydrogen Program2008 Annual Merit Review
Project PD26
WSRC-MS-2008-00098 2
Overview
Start Date: June, 2004End Date: Sept, 201050% Complete
U. High-temperature thermochemical technologyV. High temperature robust materialsNHI Objective – By 2019, operate a nuclear hydrogen production plant to demonstrate technical feasibility and cost competitiveness
Total Project Funding– DOE Share = $3.9 M (thru FY08)– Industry Cost Share = $140 K
FY07 Funding = $1400 KFY08 Funding = $1000 K
Westinghouse ElectricGiner Electrochemical (subcontract)Univ. of South Carolina (U-NERI)Sandia National Laboratory (membrane & acid system develop.)
Timeline Barriers
Budget
Partners
WSRC-MS-2008-00098 3
Objectives
The main focus of this project is to develop and demonstrate the Hybrid Sulfur thermochemical process as a viable option for large-scale hydrogen production using nuclear energy*FY08: Development and testing of an SO2 depolarized electrolyzer (SDE) using PEM-type cell design– Optimize HyS process design, update flowsheet and perform cost analysis in
conjunction with industry partner– Continue to identify and develop improved cell components to reduce sulfur
crossover and increase cell efficiency– Conduct single cell SDE tests at elevated temperature and pressure– Install and test a multi-cell SDE with 100 lph hydrogen capacity
*Can also be driven by heat from central solar receiver system
WSRC-MS-2008-00098 4
Milestones
FY07– Complete 100 hour single cell longevity test (5/15/07)– Complete construction of multi-cell stack (9/15/07)
FY08– Complete HyS flowsheet and process design (3/15/08)– Complete multi-cell stack testing (3/31/08)– Complete mid-year evaluation for membranes and
electrocatalysts (5/15/08)– Complete Phase II single cell SDE testing (9/15/08)– Complete component development and issue
report (9/15/08)
Complete
Complete
Complete
Complete
Complete
On Schedule
On Schedule
WSRC-MS-2008-00098 5
FY08 Plan and Approach
HyS Process Design Optimization– Collaboration with Westinghouse Electric– Improved flowsheet and updated plant cost analysis
Component Characterization and Development– Electrodes and electrocatalysts evaluations– Membrane selection, testing and analysis (with partners)– Assembly of single-cell membrane-electrode assemblies
Single-Cell Electrolyzer Testing– Design, assemble and test single-cell electrolyzers– Temperature, pressure and acid strength effects– Post-test examinations and analysis
Multi-cell Stack– Modify test facility for larger stack testing– Fully characterize multi-cell stack performance– Post-test examinations and analysis
90% Complete
Our approach is to analyze the overall Hybrid Sulfur process design and requirements and to perform development on the key new component, the SO2-depolarzied electrolyzer. We try to maximize use of results andexperience from programs on PEM fuel cells and PEM electrolyzers.
70% Complete
50% Complete
100% Complete
WSRC-MS-2008-00098 6
Hybrid Sulfur Process
The only 2-step, all-fluids thermochemical cycle – based on sulfur oxidation and reduction; only S-H-O compounds
Acid Decomposer
SO2 Electrolyzer
H2SO4 ½O2 + SO2 + H2O> 800°C
Heat
H2 + H2SO4 SO2 + 2H2O100°C
Electric Energy SO2 + H2OH2SO4 (H2O)
H2OH2O
H2H2
½O2½O2
Inputs:• Water• Heat (78% of energy input)• Electricity (22% input)
Outputs:• Hydrogen• Oxygen• Waste heat
WSRC-MS-2008-00098 7
SO2-Depolarized Anode Significantly Reduces Electricity Needed to Electrolyze Water
Water electrolysis half-cell reactions:H2O(l) → ½ O2(g) + 2 H+ + 2 e– anode reaction2 H+ + 2 e– → H2(g) cathode reactionH2O(l) → ½ O2(g) + H2(g) net reactionStandard cell potential, E° = -1.229 V at 25°C
SO2-depolarized electrolysis half-cell reactions:2 H2O(l) + SO2(aq) → H2SO4(aq) + 2 H+ + 2 e– anode reaction2 H+ + 2 e– → H2(g) cathode reaction2 H2O(l) + SO2(aq) → H2SO4(aq) + H2(g) net reactionStandard cell potential, E° = -0.158 V at 25°C
= -0.173 V in 30% H2SO4= -0.262 V in 50% H2SO4
WSRC-MS-2008-00098 8
Improved Flowsheet Developed in Conjunction with Westinghouse Electric
Key design improvements:Optimized heat integration between reactor, hydrogen plant and bottoming cycleImproved thermal efficiency for HyS thru pinch analysisIncreased hydrogen production per PBMR by over 150%Expected to have major impact on cost of hydrogenFinal equipment sizing and cost estimates in process
Courtesy of W. Kreil, PBMR Ltd.
WSRC-MS-2008-00098 9
SRNL’s PEM Concept forSO2-Depolarized Electrolyzer
SO2 oxidized at anode to form H2SO4 and hydrogen ionsPractical cell potential is 600 mV at 500 mA/cm2 Requires efficient thermal step to regenerate SO2 reactantPEM cell concept permits compact design, reduced footprint, and lower costLeverages development for PEM fuel cells and water electrolyzersCurrent HyS flowsheets based on operation at 100°C and 20 bar with 50 wt% H2SO4
WSRC-MS-2008-00098 10
Electrolyzer Component Development Objectives
Proton Exchange Membrane– Minimal SO2 Transport– Maximum ion conductivity
Anode– Maximum SO2 oxidation kinetics– Minimal attack by SO2/H2SO4
Cathode– Maximum hydrogen formation kinetics– Minimal reaction with SO2
Flow Field/Diffusion Media– Maximize SO2 transport to anode– Low pressure drop– Chemically and mechanically stable ca
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~200 μm
WSRC-MS-2008-00098 11
Subscale Tests Used to Characterize Key Electrolyzer Components
Glass electrolyzer unit used to measure SO2 transport thru membrane and MEA performanceCatalyst evaluated in three electrode cell
Schematic of Small-Scale (2 cm2) Electrolyzer Test Assembly
Water Jacket Concentrated Sulfuric Acid
WSRC-MS-2008-00098 12
Improved Membranes and Electrocatalysts being Developed
Conventional Nafion membranes have good conductivity, but suffer from relatively high SO2 transportImprovements of 5x versus Nafionachieved to date; new membranes sought with >10xMembranes for Direct Methanol Fuel Cells operating at higher temperatures appear attractivePlatinum is the baseline electrocatalyst; Pt alloy catalysts show improved performance and excellent stabilityPalladium electrocatalyst rejected due to poor performance and instability
0.E+00
1.E+05
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7.E+05
Rat
io (C
ondu
ctiv
ity/S
O2 T
rans
port)
Nafion
® EW 11
00
F1460
FKB
E750 (
not st
able
in SDE)
SDAPP2.2
PN117
Catalyst Evaluations
Membrane Test ResultsTesting has helped to characterize component performance and identify promising options
0.475
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-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2log i (mA/mg of metal)
Pote
ntia
l (V
vs.
SHE)
30 wt% H2SO4
Room Temperature
45 wt% Pt/C (Commercial)
45 wt% PtRu/Ru/Ox/C
30 wt% Pt3Co/C
30 wt% Pt3CoCr/C
30 wt% Pt3CoNi/C
30 wt% Pt3CoIr/C
WSRC-MS-2008-00098 13
Improving Reaction Kinetics has Biggest Impact on Cell Performance
Test results fitted with empirical equation (3 atm, 80C and 500 mA/cm2)
Kinetics 78 % of overpotentialOhmic Losses 14 %Concen. Polar. 8 %
Plan: Improved catalyst and higher operating temperature (100 - 120°C)
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0 200 400 600 800 1000Current density (mA/cm2)
Pote
ntia
l los
s due
to k
inet
ic re
sist
ance
(V)
P= 1 atmP= 2 atmP= 3 atmP= 4 atmEquilibrium Potential
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0 200 400 600 800 1000Current density (mA/cm2)
Pote
ntia
l los
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hmic
resi
stan
ce (V
) P= 1 atm
P= 2 atm
P= 3 atm
P= 4 atm
Pure membrane resistance
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0 200 400 600 800 1000Current density (mA/cm2)
Pote
ntia
l los
s due
to m
ass t
rans
port
(V)
P= 1 atm
P= 2 atm
P= 3 atm
P= 4 atm
WSRC-MS-2008-00098 14
Single-cell Testing
SO2-depolarized electrolyzer
Electrolyzer Test Facility
Single Cell Electrolyzer (60 cm2 active area)
WSRC-MS-2008-00098 15
Single Cell Test Results
Cell Voltages for MEA 25
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0 100 200 300 400 500 600 700 800
current density, mA/cm2
cell
volta
geDec 27 ambDec 28 ambDec 28 80C 5 atmDec 31 ambDec 31 80C 5 atmJan 2 amb
anolyte concentrations are nominally 30 wt%
Cell Voltage and Current
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time, hours
volts
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ent,
ampe
res
cell voltscurrent
sampleroperationand unintentionalanolyte dilution
heatup andpressurization
brief loss ofanolyte flow
intentionalvariationof current
unintentionalvariation ofcurrent
100 Hour Longevity Test Single Cell Test Results
Blue line –best ambient (MEA 14)
Red line –best at T&P (MEA 19)
Twenty-six different single cell units have been tested at up to 80°C and 6 bar. 100-hour longevity test completed. Current density up to 1100 mA/cm2 vs 500 mA/cm2 goal. Voltage at design point of 760 mV vs 600 mV goal. Higher temp and pressure plus improved catalysts expected to lower voltage.
WSRC-MS-2008-00098 16
Reduction of Sulfur Deposition is a Key Technical Objective
SO2 diffuses thru PEMReduction at cathode can result in S depositsCertain designs and operating conditions avoid depositsMultiple approaches– Modify membrane– Modify operating conditions– Alternative cell design
Membrane thickness
Pt: 90.5 wt%C: 7.87 wt%S: 0.95 wt%F: 0.68 wt%
Pt: 88.34 wt%C: 9.43 wt%S: 1.57 wt%F: 0.66 wt%
Pt: 8.54 wt%C: 44.1 wt%S: 25.14 wt%F: 22.21 wt%
Membrane thickness
Pt: 90.5 wt%C: 7.87 wt%S: 0.95 wt%F: 0.68 wt%
Pt: 88.34 wt%C: 9.43 wt%S: 1.57 wt%F: 0.66 wt%
Pt: 8.54 wt%C: 44.1 wt%S: 25.14 wt%F: 22.21 wt%
Membrane thickness
Pt: 54.03 wt%C: 41.21 wt%S: 1.66 wt%F: 3.1 wt%
Pt: 30.43 wt%C: 56.32 wt%S: 6.79 wt%F: 6.47 wt%
Pt: 0.77 wt%C: 19.63 wt%S: 75.48 wt%F: 4.12 wt%
Pt: 5.23 wt%C: 53.75 wt%S: 19.69 wt%F: 21.32 wt%
Membrane thickness
Pt: 54.03 wt%C: 41.21 wt%S: 1.66 wt%F: 3.1 wt%
Pt: 30.43 wt%C: 56.32 wt%S: 6.79 wt%F: 6.47 wt%
Pt: 0.77 wt%C: 19.63 wt%S: 75.48 wt%F: 4.12 wt%
Pt: 5.23 wt%C: 53.75 wt%S: 19.69 wt%F: 21.32 wt%
MEA 9, N117 with Pt black catalyst
MEA 20, N115 with Pt/C catalyst
S layer
WSRC-MS-2008-00098 17
Multi-cell Stack Development
Established partnership with Giner ElectrochemicalLeverages existing PEM water electrolyzer technologyMaximizes use of existing components and hardwareIncorporates SRNL experience with PEM-type SO2 electrolysisBi-polar 3-cell stack using round plates with 160 cm2
active area per cellRated capacity is 100 lph of hydrogen production under SO2-depolarized conditions
3-cell SDE
WSRC-MS-2008-00098 18
Multi-Cell Stack Testing Completed
• Level 1 Milestone Completed on 3/26/08 (ahead of schedule)• Demonstrates 8x scale-up and multi-cell stack capability• Key step leading to larger scale demonstration plant
Cell Voltage and Current for Multi-Cell Stack
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time, hours
volts
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curr
ent,
ampe
res
supply voltsstack voltscell 1cell 2cell 3current
WSRC-MS-2008-00098 19
Future Work
FY08– Continue component development of improved cell membranes and
electrocatalysts; select design for integrated lab-scale test– Characterize promising components in single cell tests – Verify solution to sulfur crossover issue– Continue work with industry, lab and university partners on alternative
cell design approachesFY09:– Continue electrolyzer development; identify optimum membrane; extend
operation to more severe conditions; scale-up to larger capacities– Modify test facility for higher temp operation (>100°C)– Run single cell tests at higher temp and for extended time (>1000 hour)– Design and build an Integrated Lab-Scale Experiment of HyS, including
high temperature acid decomposition and SO2/O2 separation
WSRC-MS-2008-00098 20
Summary
Relevance HyS Process combined with advanced nuclear reactors (or solar receiver) can be an important hydrogen production optionApproach Develop PEM-based SO2-depolarized electrolyzer and combine with acid decomposition system from SI project. Maintainbalanced program including cell development and system testing.Technical Accomplishments Key cell components defined; longevity test completed; multi-cell stack demonstrated; high efficiency HyS flowsheet completedTechnology transfer/collaborations Active partnership with Westinghouse on plant design; partnership with Giner on electrolyzer manufacture; collaborations with USC, SNL and several other university partnersFuture Work Complete electrolyzer development and scale-up; demonstrate complete cycle in an integrated lab-scale experiment
