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LUND UNIVERSITY LIBRARIES

Characterisation of Ionic Liquid doped Polybenzimidazole Membranes for Application in High-Temperature Proton Exchange Membrane Fuel Cells

Jacobsson Trönndal, Adam LU (2023) KETM05 20231
Chemical Engineering (M.Sc.Eng.)
Abstract
In this study four membranes were tested and evaluated against each other for use in high-temperature proton exchange membrane fuel cell (HT-PEMFC) applications. A phosphoric acid (PA) doped polybenzimidazole (PBI) membrane, was used as a reference as the current state-of-the-art. The charge carrier in this membrane is the PA, and there are advantages in switching from PA to ionic liquid (IL) as the charge carriers in HT-PEMFC, such as to reduce leaching and lost performance over time. Two of the membranes investigated in this study were PBI mixed with the commercial ILs [dema][TfO] and [HEIm][TFSI]. The last membrane was a mixture of PBI and a newly synthesized IL by Chalmers University of Technology, [FA][TFSI]. Conductivity... (More)
In this study four membranes were tested and evaluated against each other for use in high-temperature proton exchange membrane fuel cell (HT-PEMFC) applications. A phosphoric acid (PA) doped polybenzimidazole (PBI) membrane, was used as a reference as the current state-of-the-art. The charge carrier in this membrane is the PA, and there are advantages in switching from PA to ionic liquid (IL) as the charge carriers in HT-PEMFC, such as to reduce leaching and lost performance over time. Two of the membranes investigated in this study were PBI mixed with the commercial ILs [dema][TfO] and [HEIm][TFSI]. The last membrane was a mixture of PBI and a newly synthesized IL by Chalmers University of Technology, [FA][TFSI]. Conductivity measurements, polarisation curves and electrochemical impedance spectroscopy (EIS) were done to characterise and evaluate the membranes.
The study shows that these IL-PBI membranes have a long way to go to be a commercially competitive technique compared to PA-PBI membranes. In the report it can be seen that all the IL-PBI membranes show very poor performance without the addition of PA. Even with the addition of PA, the performance of the IL-PBI membranes cannot compare to PA-PBI membranes, being a factor 10 lower in the conductivity test and polarisation curves. In the EIS the membrane that got a conductivity closest to PA-PBI was [FA][TFSI]-PBI that had a conductivity that was 70% of the conductivity of PA-PBI. The lower performance for the membranes in the polarisation measurements compared to the EIS can be due to several factors such as changed membrane resistance with applied load or the influence of other cell resistances. Tests where the membranes were doped with the corresponding IL in the electrodes instead of PA also showed poor performance.
Future studies in the field of IL-PBI membranes are needed for the technology to become viable as an alternative to PA-PBI. (Less)
Abstract (Swedish)
I denna studie testades och utvärderades fyra membran mot varandra för användning i högtemperaturprotonutbytesmembranbränslecell (HT-PEMFC) applikationer. En fosforsyra (PA)-dopat polybensimidazol (PBI)-membran användes som en referens som den nuvarande state-of-the-art. Laddningsbäraren i detta membran är PA, och det finns fördelar med att byta från PA till jonisk vätska (IL) som laddningsbärare i HT-PEMFC, som att minska urlakning och förlorad prestanda över tid. Två av membranen som undersöktes i denna studie var PBI blandat med de kommersiella ILs [dema][TfO] och [HEIm][TFSI]. Det sista membranet var en blandning av PBI och en nysyntetiserad IL av Chalmers tekniska högskola, [FA][TFSI]. Konduktivitetsmätningar, polarisationskurvor och... (More)
I denna studie testades och utvärderades fyra membran mot varandra för användning i högtemperaturprotonutbytesmembranbränslecell (HT-PEMFC) applikationer. En fosforsyra (PA)-dopat polybensimidazol (PBI)-membran användes som en referens som den nuvarande state-of-the-art. Laddningsbäraren i detta membran är PA, och det finns fördelar med att byta från PA till jonisk vätska (IL) som laddningsbärare i HT-PEMFC, som att minska urlakning och förlorad prestanda över tid. Två av membranen som undersöktes i denna studie var PBI blandat med de kommersiella ILs [dema][TfO] och [HEIm][TFSI]. Det sista membranet var en blandning av PBI och en nysyntetiserad IL av Chalmers tekniska högskola, [FA][TFSI]. Konduktivitetsmätningar, polarisationskurvor och elektrokemisk impedansspektroskopi (EIS) gjordes för att karakterisera och utvärdera membranen.
Studien visar att dessa IL-PBI-membran har en lång väg att gå för att vara en kommersiellt konkurrenskraftig teknik jämfört med PA-PBI-membran. I rapporten kan man se att alla IL-PBI-membran uppvisar mycket dålig prestanda där PA inte är tillsatt. Även med tillägg av PA kan IL-PBI-membranens prestanda inte jämföras med PA-PBI-membranen, eftersom de är en faktor 10 lägre i konduktivitetstestet och polarisationskurvorna. I EIS var det membran som fick en konduktivitet närmast PA-PBI [FA][TFSI]-PBI som hade en konduktivitet som var 70% av PA-PBI. Den lägre prestandan för membranen i polarisationsmätningarna jämfört med EIS kan bero på flera faktorer såsom förändrat membranresistans med applicerad belastning eller påverkan av andra cellresistanser. Tester där membranen dopats med motsvarande IL i elektroderna istället för PA visade också dålig prestanda.
Framtida studier inom området IL-PBI-membran behövs för att tekniken ska bli livskraftig som ett alternativ till PA-PBI. (Less)
Popular Abstract
Ionic Liquid doped Membranes for Fuel Cells

The planet is heating up and we are in a climate crisis. Numerous sources are telling us this, from the UN to the IPCC are very clear that several actions need to be taken to combat this negative trend and to avoid even larger catastrophes in the future. The UN is listing the heating and power sector as the number one contributor to global warming and being the largest emitter of carbon dioxide in the world followed by the transport sector. In Sweden, however, with its developed renewable energy the main emitter of green house gases, like carbon dioxide, is the transport sector. There is therefore a lot to win by focusing on reducing the emission from the transport sector globally, and... (More)
Ionic Liquid doped Membranes for Fuel Cells

The planet is heating up and we are in a climate crisis. Numerous sources are telling us this, from the UN to the IPCC are very clear that several actions need to be taken to combat this negative trend and to avoid even larger catastrophes in the future. The UN is listing the heating and power sector as the number one contributor to global warming and being the largest emitter of carbon dioxide in the world followed by the transport sector. In Sweden, however, with its developed renewable energy the main emitter of green house gases, like carbon dioxide, is the transport sector. There is therefore a lot to win by focusing on reducing the emission from the transport sector globally, and especially in Sweden.
There are several technologies that can be a piece of the puzzle in the transformation of the transport sector. The largest of these today is the battery electric vehicle (BEV) that already have been established on the market as a green alternative. There are some problems with batteries, like the recyclability that could lead to needing to build new batteries more often. This could be a problem environmentally by itself. Another problem is that batteries need to become very large to be able to drive large vehicles, like trucks or boats. Therefore, there has been research into fuel cell electric vehicles (FCEV) that use an external fuel to produce electricity. There are some commercial FCEV on the market today, but it is still in the early stages. Most of these uses proton exchange membrane fuel cells (PEMFC) as its electricity generator. These uses hydrogen and air as fuel that together creates water and electricity.
Today’s PEMFC are mostly operating at low temperatures such as 80℃ (LT-PEMFC) and have fairly high efficiency but it can get better by raising the temperature. By operating at higher temperatures, for example 160℃ (High Temperature PEMFC or HT-PEMFC), another problem can also be solved. Flooding of membranes in LT-PEMFC is a problem which can occur as to much water is produced in the process contra the amount of water removed with the exhaust. By raising the temperature, the water is in gases form and wont flood the membrane. However, the membranes does not conduct proton well without water so another proton carrier is needed and today the most used proton carrier is phosphoric acid. Phosphoric acid is a strong acid that can leach and damage the cell in long time use and another way of conducting protons in HT-PEMFC is being searched for.
One possible solution is the mix the membrane with ionic liquid when casting the membrane to by this improving the dry membrane’s ability to conduct proton. Ionic liquids are liquids that are entirely composed of ions and therefore have a high charge density. The idea is that by adding ionic liquid, no other doping is needed. However, when testing these membranes in three different tests (a conductivity test, polarisation curve test and electrochemical impedance spectroscopy) the membranes that have been doped with ionic liquid does not perform as well as the state-of-the-art membrane for HT-PEM, which is a PBI membrane doped with phosphoric acid.
There can be many reasons why these does not perform well in the test, but one possible answer is that when the ionic liquid is casted with the PBI membrane and solidifies the mobility of the ions decrease and therefore can not conduct protons very well. Another reason could be that the membranes might not be homogeneous, with some parts being more ionic liquid and other parts being more PBI.
When doping these ionic liquid doped membranes with phosphoric acid the result improves. When adding a drop of phosphoric acid the newly synthesised ionic liquid, [FA][TFSI], doped membrane performed better at the in cell test than the commercial ionic liquid, [dema][TfO] and [HEIm][TFSI], doped membranes. Neither is close to competing with phosphoric acid doped PBI membranes, however, and more research and thoroughly looking closer at the ionic liquid doped membranes is needed to determine what could be improved in these. (Less)
Please use this url to cite or link to this publication:
author
Jacobsson Trönndal, Adam LU
supervisor
organization
course
KETM05 20231
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Fuel cells, Phosphoric acid, Polybenzimidazole, PA-PBI, Ionic liquid, IL, High temperature proton exchange membrane fuel cell, HT-PEMFC, Electrochemical impedance spectroscopy, EIS, IL-PBI, Chemical engineering
language
English
id
9134845
date added to LUP
2023-09-27 09:33:16
date last changed
2023-09-27 09:33:16
@misc{9134845,
  abstract     = {{In this study four membranes were tested and evaluated against each other for use in high-temperature proton exchange membrane fuel cell (HT-PEMFC) applications. A phosphoric acid (PA) doped polybenzimidazole (PBI) membrane, was used as a reference as the current state-of-the-art. The charge carrier in this membrane is the PA, and there are advantages in switching from PA to ionic liquid (IL) as the charge carriers in HT-PEMFC, such as to reduce leaching and lost performance over time. Two of the membranes investigated in this study were PBI mixed with the commercial ILs [dema][TfO] and [HEIm][TFSI]. The last membrane was a mixture of PBI and a newly synthesized IL by Chalmers University of Technology, [FA][TFSI]. Conductivity measurements, polarisation curves and electrochemical impedance spectroscopy (EIS) were done to characterise and evaluate the membranes. 
The study shows that these IL-PBI membranes have a long way to go to be a commercially competitive technique compared to PA-PBI membranes. In the report it can be seen that all the IL-PBI membranes show very poor performance without the addition of PA. Even with the addition of PA, the performance of the IL-PBI membranes cannot compare to PA-PBI membranes, being a factor 10 lower in the conductivity test and polarisation curves. In the EIS the membrane that got a conductivity closest to PA-PBI was [FA][TFSI]-PBI that had a conductivity that was 70% of the conductivity of PA-PBI. The lower performance for the membranes in the polarisation measurements compared to the EIS can be due to several factors such as changed membrane resistance with applied load or the influence of other cell resistances. Tests where the membranes were doped with the corresponding IL in the electrodes instead of PA also showed poor performance.
Future studies in the field of IL-PBI membranes are needed for the technology to become viable as an alternative to PA-PBI.}},
  author       = {{Jacobsson Trönndal, Adam}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Characterisation of Ionic Liquid doped Polybenzimidazole Membranes for Application in High-Temperature Proton Exchange Membrane Fuel Cells}},
  year         = {{2023}},
}