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Performance degradation of Molten Carbonate Fuel Cells caused by SO2 in simulated flue gas
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-8755-2972
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0002-2268-5042
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9203-9313
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effect on MCFC performance degradation SO2 contaminant at the cathode, in combination with operating the fuel cell with CO2 lean oxidant gas, simulating combustion flue gas, was evaluated. Of special focus was the effect of electrolyte degradation.

 Measurements were performed to test the effect of SO2 in the oxidant gas stream, followed by regeneration with clean gas. A 3cm2 button cell MCFC allowing active electrolyte management by refilling was for 1500h to benchmark the performance degradation without contaminants. In order to study the poisoning effect of SO2 entering the fuel cell gas, the MCFC was operated for 250h with the addition of 18ppm SO2 in the oxidant gas. Electrolyte was added after 1500h of benchmark operation and after 250h of contaminant operation. The addition of 18ppm SO2 greatly accelerated the performance degradation of the fuel cell. Measurements showed that the internal resistance was the single factor which was most affected by the SO2 poisoning, and that the performance degradation after 250h was not reversed by regeneration with clean gas, but with the addition of fresh electrolyte. This led us to conclude that SO2 in oxidant gas leads to an accelerated loss of electrolyte and subsequent decrease in conductivity of the electrolyte, causing loss of performance and meeting end of life criteria after relatively short operational time. Other factors, such as poisoning of the anode and corrosion of cathode side current collectors, were also detected. 

Keyword [en]
Molten Carbonate Fuel Cell, MCFC, CO2 separation, flue gas, SO2 contaminant
National Category
Other Chemistry Topics
Research subject
Chemical Engineering
URN: urn:nbn:se:kth:diva-154584OAI: diva2:757948
EU, European Research Council, 245171

QS 2014

Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2014-10-28Bibliographically approved
In thesis
1. Applications for Molten Carbonate Fuel Cells
Open this publication in new window or tab >>Applications for Molten Carbonate Fuel Cells
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Molten Carbonate Fuel cells are high temperature fuel cells suitable for distributed generation and combined heat and power, and are today being installed on commercial basis in sizes from 100kW to several MW. Novel applications for MCFC which have attracted interest lately are MCFC used for CO2 separation from combustion flue gas, and high temperature electrolysis with reversible fuel cells. In the first application, the intrinsic capability of the MCFC to concentrate CO2 from the cathode to the anode side through the cell reaction is utilized. In the second application, the high operating temperature and relatively simple design of the MCFC is utilized in electrolysis, with the aim to produce a syngas mix which can be further processed into hydrogen of synthetic fuels.

In this thesis, the effect on fuel cell performance of operating a small lab-scale molten carbonate fuel cell in conditions which simulate those that would apply if the fuel cell was used for CO2 separation in combustion flue gas was studied. Such operating conditions are characterized especially by a low CO2 concentration at the cathode compared to normal operating conditions. Sulfur contaminants in fuel gas, especially H2S, are known poisoning agents which cause premature degradation of the MCFC. Furthermore, combustion flue gas often contains sulfur dioxide which, if entering the cathode, causes performance degradation by corrosion and by poisoning of the fuel cell. This makes poisoning by sulfur contaminants of great concern for MCFC development. In this thesis, the effect of sulfur contaminants at both anode and cathode on fuel cell degradation was evaluated in both normal and in low CO2 simulated flue gas conditions.     

The results suggested that the poisoning effect of SO2 at the cathode is similar to that of H2S at the anode, and that it is possibly due to a transfer of sulfur from cathode to anode. Furthermore, in combination with low CO2 conditions at the cathode, SO2 contaminants cause fuel cell poisoning and electrolyte degradation, causing high internal resistance.

By using a small lab-scale MCFC with commercial materials and standard fuel cell operating conditions, the reversible MCFC was demonstrated to be feasible. The electrochemical performance was investigated in both fuel cell (MCFC) and electrolysis cell (MCEC) modes. The separate electrodes were studied in fuel cell and electrolysis modes under different operating conditions. It was shown that the fuel cell exhibited lower polarization in MCEC mode than in MCFC mode, and a high CO2 concentration at the fuel cell anode reduced the polarization in electrolysis mode, which suggested that CO2 is reduced to produce CO or carbonate.

Abstract [sv]

Smältkarbonatbränsleceller (MCFC) är en typ av högtemperaturbränsleceller som är anpassade för kombinerad el- och värmeproduktion i mellan-till stor skala. Idag installeras MCFC på kommersiell basis i storlekar mellan 100kW och flera MW. En ny typ av tillämpning för MCFC som har väckt intresse på senare tid är användandet av MCFC för CO2-avskiljning i kombination med konventionell elproduktion genom förbränning. En annan ny tillämpning är högtemperaturelektrolys genom användandet av reversibla bränsleceller. I det första fallet utnyttjas att CO2 kan koncentreras från katod- till anodsidan, vilket sker genom cellreaktionen för MCFC. I det andra fallet utnyttjas den höga arbetstemperaturen och den relativt enkla cell-designen för att använda reversibla MCFC till elektrolys, med syfte att producera en syngas-blandning som kan förädlas till vätgas eller till syntetiskt bränsle.

I denna avhandling studeras effekten på bränslecellens prestanda genom att operera en MCFC i lab-skala med driftförhållanden som simulerar de som förväntas uppkomma om bränslecellen användes för CO2-avskiljning ur rökgaser från förbränning. Dessa driftförhållanden karaktäriseras av låg CO2-koncentration på katodsidan jämfört med normal drift. Svavelföroreningar i bränsle, speciellt H2S, är kända för att orsaka förgiftning av anoden, vilket i sin tur försämrar bränslecellens prestanda. Dessutom innehåller rökgaser ofta SO2, vilket antas orsaka korrosion och förgiftning av katoden. Detta gör effekten av svavelföroreningar till ett prioriterat ämne för utvecklingen av MCFC. I denna avhandling undersöks effekten av svavelföroreningar på både anod- och katodsidan, i normala driftförhållanden och i förhållanden med låg CO2 som simulerar användandet av rökgaser för CO2-avskiljning. Resultaten tyder på att effekten av förgiftning med SO2 på katoden liknar den med H2S på anoden, och att detta kan vara orsakat av en transport av svavel från katod till anod. Vidare, i kombination med låg CO2 koncentration på katoden så orsakar SO2-föroreningar elektrolytdegradering, vilket orsakar hög inre resistans.

Genom att använda en liten MCFC i lab-skala med kommersiella material och standardförhållanden för MCFC påvisades att reversibla smältkarbonatbränsleceller kan vara ett lovande koncept. Den elektrokemiska prestandan av både cell och separata elektroder undersöktes både som bränslecell (MCFC)och vid elektrolys (MCEC). Resultaten visade att cellen uppvisade lägre polarisation vid elektrolys än som bränslecell, och att ten hög CO2-koncentration på det som är bränslecellens anodsida gav upphov till en minskad elektrodpolarisation, vilket indikerar att CO2 reduceras för att producera CO eller karbonat.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xii, 62 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:51
Molten Carbonate Fuel Cell (MCFC), poisoning, electrolyte degradation, SO2, Electrochemical Impedance Spectroscopy (EIS), CO2 separation, button cell set-up; reversible molten carbonate fuel cell, high temperature electrolysis.
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
urn:nbn:se:kth:diva-154585 (URN)978-91-7595-326-7 (ISBN)
Public defence
2014-11-14, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)

QC 20141028

Available from: 2014-10-28 Created: 2014-10-23 Last updated: 2014-11-03Bibliographically approved

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