Hydrogen Fuel Quality - Energy
Transcript of Hydrogen Fuel Quality - Energy
Hydrogen Fuel Quality The Year In Review
E. Brosha, F. Garzon, R. Mukundan, C. Padró,T. Rockward (presenter)
Los Alamos National LaboratoryJune 12, 2008
Project ID # SCS4
This presentation does not contain any proprietary, confidential, or otherwise restricted information
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Overview
• Project start date: 10/1/06• Project end date: 9/30/11• Percent complete: 30%
• Barriers addressed– I. Conflicts between Domestic and
International Standards– N. Insufficient Technical Data to
Revise Standards
• Total project funding: $1,100K– DOE share: 100%– Contractor share
• Funding received in FY07: $250K• Funding for FY08: $850K
Timeline
Budget
Barriers
• University of Hawaii/HNEI• University of Connecticut• University of South Carolina• Clemson University• SRNL• NIST• NREL• ANL
Partners/Collaborators
Milestones & Deliverables
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Month/Year Milestone or Deliverable
Dec-07 Milestone: Evaluate sensitivity of H2S specific ion analysis methods. Completed
Mar-08 Milestone: Evaluate cross interference effects of H2S specific ion analysis methods. Completed
Jun-08 Deliverable: Report on analytical methods development. CompletedMilestone: Determine tolerable impurity level specifications forhydrogen fuels. Completed sulfurMilestone: Evaluate sensitivity of NH3 specific ion analysis methods. In progress*
Sep-08 Milestone: Evaluate cross interference effects of NH3 specific ion analysis methods. Milestone: Demonstrate proof of concept of CO analysis by electrochemical methods.
* Status as of 4/18/08
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Technical Approach
• Conduct gauge studies with testing labs and address experimental differences, thus increasing the confidence in the data.
• Create and standardize a Data Reporting Format• Develop and test new analytical methods for detecting
ppb levels of contaminants.• Test the critical constituents (NH3, CO, and H2S) and
provide data sets to FC modelers to establish predictive mechanistic models.
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LANL’s role in understanding the impact offuel impurities
Subtask 2.1: Fuel Quality Impacts• to gain confidence in fuel cell results from the different test labs
involved in hydrogen quality efforts by conducting a gauge study. (DOE Round Robin)
• to provide all the relevant information necessary for reproducing experiments and, more importantly, to supply useful information to modelers, MEA manufacturers, hydrogen suppliers and OEMs.
Subtask 2.2: Analytical Methods Development• to develop and/or modify existing analytical techniques to detect
fuel impurities in the ppb (10-9) range.• to test and determine the impact of CO, H2S, and NH3 in the fuel
stream in order to develop a hydrogen fuel quality standard.
These analytical techniques will develop the tools to be able toaccurately measure impurities at the proposed standards level
About the Fuel Impurities Effects:
The focus is to understand the fundamental interactions and mechanism of impurities on fuel cell performance, including the investigation & development of mitigating strategies and recovery techniques. These efforts are geared towards meeting DOE’s 2010 and 2015 Pt loadings. Data generated in these activities are directly communicated to the modeling effort.
The two tasks are separate but complimentary in that they leverage one another. The Fuel Impurities solicitation winners participated in the LANL-led DOE Round Robin to ensure consistent testing procedures and data collection. The learnings from the Fuel Impurities Efforts help establish testing priorities in the Hydrogen Quality effort.
On PEFC Performance On Developing Codes and Standards
This effort consists of several collaborators: UConn, Clemson, SRNL, University of S. Carolina, NIST, and HNEI.
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The VI-curves were:• Taken after completing a break-in procedure (0.6V for 1 hr then cycled 20 minutes at 0.5 and
0.7V for 6 hrs, overnight at 30A (cc))• Run in constant current mode using 1.2/2.0 stoichs (H2/Air) until deviation ≤ 5 mV from the
previous VI-curves at multiple points (Pressurized and Ambient)
The average of the last 3 VI-curves was submitted for a Round Robin Study.
Technical Accomplishments DOE Round Robin Results
Round Robin Test Cell No. 2N112, 50cm2
A/C: 0.2 mg Pt/cm2Tcell: 80oC; P: 25 psig(sea-level); Fully humidified
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Current Density/ A*cm-2
Run 1Run 2Run 3Run 4Run 5Run 6
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The VI-curves were:• Taken after completing a break-in procedure (0.6V for 1 hr then cycled 20 minutes at 0.5 and
0.7V for 6 hrs, overnight at 30A (cc))• Run in constant current mode using 1.2/2.0 stoichs (H2/Air) until deviation ≤ 5 mV from the
previous VI-curves at multiple points (Pressurized and Ambient)
The average of the last 3 VI-curves was submitted for a Round Robin Study.
Technical Accomplishments DOE Round Robin Results, Cont.
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Round Robin Test Cell No. 2 N112, 50cm2
A/C: 0.2 mg Pt/cm2
Tcell: 60oC; P: Ambient (sea-level); Fully humidified
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Technical Accomplishments DOE Round Robin Results, Cont.
• Before and after tests showed nearly identical results, thus making the round robin results valid for comparison.
• Largest difference observed in Mass Transport Region• Further analysis/tests to probe those differences
Round Robin Test Cell No. 2N112, 50cm2
A/C: 0.2 mg Pt/cm2Tcell: 80oC; P: 25 psig(sea-level); Fully
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Initial ResultsSubsequent Results2 mV
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humidified
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Technical Accomplishments DOE Round Robin Results, Cont.
• Before and after tests showed nearly identical results, thus making the round robin results valid for comparison.
• Largest difference observed in Mass Transport Region• Further analysis/tests to probe those differences
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Current Density/ A*cm^2
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Technical Accomplishments DOE Round Robin Results, Comparisons
• Overall good agreement between sites, discussions are on-going to address differences.
• Other test sites have expressed interested in the cell and are scheduled to test.
• Final Report in progress
Round Robin Test Cell No. 2N112, 50cm2
A/C: 0.2 mg Pt/cm2Tcell: 80oC; P: 25 psig(sea-level); Fully humidified
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TROUCONNUSCClemson-SRNLLANL RE-TEST
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The document’s objective is to describe in detail all the information necessary to describe and/or reproduce the performed contaminant experiment
Contaminant Experiment
MEA & Gasketing
Hardware & Heating
Start up procedurePolarization Curve
H2 Crossover TestsCV experiment
Data Reporting Format
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Data Reporting Formatexcerpt from start-up procedure
FC Operating ConditionsDiagnostic Identifier (e.g. MEA 012) LANL_TR040908Gas TypeAnode Gas Composition & Quality(e.g. 100% H2, 99.999%) electrolysis gradeCathode Gas Composition & Quality(e.g. oiless compressor, in-house produced) oiless compressorStoichiometry ModeFlow Tracking (yes / no) yesFlowsAnode Stoich (e.g. 1.2 or N/A) 1.2Cathode Stoich (e.g. 2.0, or N/A) 2Anode Fixed Flow (e.g. 1200 sccm, or N/A) n/aCathode Fixed Flow (e.g. 3 NL/min, N/A) n/aMinimum Flowminimum anode flow setpoint (e.g. 80 sccm, or flow at 0.2 A/cm2) 80 sccm
minimum cathode flow setpoint (e.g. 80 sccm, or flow at 0.2 A/cm2) 343 sccm
TemperaturesCell (°C) 80oCHumidification
Anode Humidifier w/o Contaminant (°C)
80oCAnode Humidifier w Contaminant (°C) by passAnode RH (%) 100%Cathode Humidifier (°C) 80°CCathode RH (%) 100%PressuresAnode Inlet (psia)Anode exit (psia) 30Cathode Inlet psia)Cathode exit (psia)
30Start-Up Procedure(e.g. Company A's Protocol, cycling from 0.2-0.7V until currents stabilize) LANL protocol
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TIME/ HR
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Ammonia StudiesEffects of 1ppm
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1.0 A/cm2
N112, 50cm2, 80oCA/C: 0.2 mg Pt/cm2
40 A(cc), fully humidified
N112, 50cm2, 80oCA/C: 0.1/0.2 mg Pt/cm2
40 A(cc), fully humidified
The graph on the left shows reproducibility after two different cells were exposed to 1 ppm NH3. Losses observed were ~70 mV.
The graph on the right shows the impact of NH3 at 0.4 and 1 A/cm2. Clearly, the losses become more pronounced at the higher current density. The data show that with more water, the NH4
+
migrates to the cathode faster.
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• 100 ppb CO showed ~5 mV loss over 300 hrs• 200 and 300 ppb CO showed ~30 mV• Some CO adsorption detected by CV
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Time/ Hrs
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N112, 50cm2, 80oCA/C: 0.2 mg Pt/cm2
40 A(cc), fully humidified
Carbon Monoxide Studies
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H2S StudiesN112, 50cm2, 80oC
A/C: 0.05/0.2 mg Pt/cm2
40 A(cc), fully humidified
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Time/ Hours
50 ppb H2S
> 300 mV
• Sulfur chemisorption onto Pt-sites deactivating the catalyst for hydrogen dissociation• Other in-house results indicate sulfur crosses over to the cathode• Low levels of sulfur can disable a fuel cell• An increase in local water decreases the sulfur impact
Relative Humidity
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Analytical Methods for ppb H2S Determination
• Chemical trap used to capture all H2S– pH>12 to insure S= species in solution
(1M NaOH + ascorbic acid and EDTA); flow rates optimized for 100% capture of H2S
• Ag/AgS electrode, sulfide ion probe– Mode 1: EMF converted to [S=] using
calibration data for qualitative determinations
– Mode 2: Electro-titration: Pb+2 titration is used in combination with EMF endpoint determination to validate mass of H2S captured
• Isothermal measurement to ensure accurate calibration is maintained
• H2S delivery to experiment must be optimized to prevent adsorptive losses
Isothermal bath
Submersible stirrer
d[S=]dt
[H2S] *Flow rate *1 mole22,400 ml
Vtrap=
H2S in
E = Eo +SLog10XE = measured electrode potentialEo= reference potential set by ref. solutionS = electrode slope ( typically -27 to -30 mV )X = activity of S= in solution
[S=] may be found usingprobe EMF and an accurate calibration against standards using where
Commercial Ion-Selective Probes
• Not suitable to directly measure [S=] even when concentrating with a trap• Problems with probe sensitivity at low sulfide ion concentrations
– Addition of small quantities of H2S in trap can be seen as a change in EMF but calculation of [S=] from these small EMF changes is overwhelmed by a summation of many errors
• One may only obtain a calibration “window”– Repeated testing of commercial probes shows that only an average calibration curve
may be obtained• Probe drift during extended immersions in trapping solution
– Long immersions in solutions with a fixed [S=] show drift versus time• Accuracy of sulfide ion concentration in solutions used for
standardization– Na2S and Na2S•9H2O typically used to prepare standard solutions may contain large
percentages of excess water and even sodium sulfate– Calibration standards prepared using calculation of initial [S=] based on weight is not
acceptable• H2S delivery to experiment must be optimized to prevent adsorptive
losses
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EMF
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EMF 11/27/07Calculated
Pro
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Log (X) mole/L
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EMF Response to trap solution ONLY
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Actual EMF of 10 -6 M Na2S measured directly
EMF 10-6 M Na2S calculated using
probe slope
EMF of 10 -5 M Na2S measured using standard
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5 ppm of H2S in Ar can easily be seen by ion probe.
Problem: Commercial sulfide ion probes begin to lose sensitivity below 10-5 M [S=]
These data to the right clearly demonstrate that the commercial ion probe is unable to differentiate a premixed 10-6 M [S=] from neat buffer solution.
5 min addition should increase [S=] by 1 µM
Experimental Evidence
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11/1/07 - Bad Ref Solution11/2/07 - Renewed Ref Sol'n8/29/07 Calibration9/4/07 "9/12/07 "9/17/07 "9/25/07 "10/1/07 "
Pro
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Measured EMF in 10 -4M [S=]
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This voltage window relatesto a large difference in "measured" sulfide ion concentration.
REMEMBER Nernst Eq. is a LOG relation
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EMF Day 1EMF next day+4 days13 days15 days
EM
F (V
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Log(X) Titration
"Isothermal exp, 15 hrs
Tracking of calibration curve data over numerous preparations of standard solutions show that there is an average EMF associated with each decade of [S=] ion concentration. Also, this plot shows how the KNO3 reference solution must be periodically serviced.
… with experiments that document the inherent drift in the ion probe …
…means that a measured EMF does not lead to a well-defined [S=].
Taken together …
Knowing the origin of these errors, new analytical H2S techniques have been developed using selective ion probe techniques.
• Titrations performed using the ion probe as an end point indicator greatly improves the accuracy and precision of the sulfide ion probe measurement.– Dropwise additions of known quantity and
[Pb+2] of lead nitrate or lead perchlorate titrant permit calculation of [S=].
• Well defined [Pb+2] titrant solutions may be easily prepared. – No water uptake in the salt.– Commercially prepared lead perchlorate
solutions available.• Isothermal operation (26°C).• Quick analysis means no time for probe
drift.• Calibration curve and standards are not
necessary.• Accurate gas flow control corrected for
temperature and pressure using precision MKS mass flow controllers.
Precise measurement of time and flow rate and [S=] using ion probe titration methods permits calculation of concentration of trace H2S in gases, crossover rates, surface area probe, etc.
Gas with trace [H2S]
The H2S is integrated long enoughto bring [S=] into range of high accuracy for the ion probe titrationtechnique.
Once enough H2S has been trapped, performtitration and calculate [S=].
E.g. 100ppb H2S in Ar could be measured withina day’s integration time.
Experimental verification of [S=] calculation using [Pb+2] titration
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titration_7052204
EMF
EM
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robe
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• Use of Pb(NO3)2 at a concentration 10x of anticipated [S=] may be titrated using the ion probe as an endpoint indicator.
• The first application was to accurately measure the true Na2S concentration being used as stock standard for probe calibration.
• TGA analysis of Na2S “anhydrous”from Alfa contained
– 4 wt% H2O– 19 wt% Na2SO4– Possibility of inert substances?
• [S=] was measured by ISE probe titration using [Pb+2] of 3.089e-2M
– Theoretical [S=] correcting mass of Na2S for water and sulfate content :
– Using titration curve data (right) :2.02e-3M
2.00e-3 ± 4.24e-5 M 0
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c.p
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Energy (KeV)
Pb
XRF is being used to corroborate titrations of µM or lower solutions
Titrated solutions may be analyzed for PbS precipitate.
The presence of Pb on trapped in filter paper confirms the presence of S.
Error reflects error in volume measurement and TGA analysis of lead salt.
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Technical Accomplishments Summary
• Completed DOE Round Robin Testing• Developed a Data Reporting Format
– Accepted by ISO TC197 Working Group 12– Proposed for adoption as part of standard
• Developed analytical method for measuring and determining ppb levels of sulfur
• Tested critical constituents (NH3, CO, and H2S)
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Future Work
• Complete final report on DOE Round Robin Testing
• Finalize the Data Reporting Format– Awaiting input from Japan, Europe, and Korea
• Optimize our analytical method and modify it for the other critical constituents
• Continue testing the critical constituents (NH3, CO, and H2S) and populating the test matrix
• Continue providing data sets and interacting with FC modelers