Abstract
The cost-effective mass production of high-performance catalyst coated membranes (CCM) for use in polymer electrolyte fuel cells (PEFCs) is a major challenge for economic viability of this promising clean and sustainable technology. Highly scalable coating methods for the manufacturing already exist for other technologies and are in the process of implementation for fuel cell manufacturing. Thereby, speed and volume of production has already been vastly increased in the last decade and a reduction of the production costs by economy of scale is in reach 1,2.
However, another major cost contribution are raw materials, which are barely affected by upscaling. It is thus crucial to achieve high performance with as little platinum as possible and at high voltages3–8. This leads to considerable developmental effort towards developing advanced catalysts7,8 combined with extensive parametric studies aiming at determining the effect of ionomer type and content as well as carbon microstructure on polarization performance3–5.
While polarization curves are irreplaceable for the characterization of PEFCs, the nature and extend of the voltage losses at various current densities cannot always be determined without performing time consuming additional experiments, screening various combinations of catalyst coated membranes, operating conditions and even experimental setups3,4. Electrochemical impedance spectroscopy (EIS) on the other hand can give an extensive insight into the nature and extent of voltage loss mechanisms with very fast scan rates without the need to interrupt fuel cell operation9,10 and can therefore accelerate material development efforts. There are however still some unanswered questions about the interpretation of the EIS signals for PEFC.
To address this lack of understanding, we performed an extensive experimental campaign examining the influence of gas pressure, gas relative humidity, gas flow rate, catalyst layer ionomer content and catalyst layer thickness. Thereby, the impact of reactant concentration, water concentration, supply and removal of reactants and products to and from the active sites is quantified. These are all processes that can be seen in the impedance spectrum. By variation of the controlling parameters a better understanding of the spectrum can be obtained. We continued the experimental and empirical modelling work based on previously published work that was mainly concerned with the influence of catalyst layer thickness and ionomer content9 and added important experimental data from a variation of operating conditions. In the present work, we delve deeper in the experimental results obtained and present an equivalent circuit model that facilitates EIS data interpretation.
However, another major cost contribution are raw materials, which are barely affected by upscaling. It is thus crucial to achieve high performance with as little platinum as possible and at high voltages3–8. This leads to considerable developmental effort towards developing advanced catalysts7,8 combined with extensive parametric studies aiming at determining the effect of ionomer type and content as well as carbon microstructure on polarization performance3–5.
While polarization curves are irreplaceable for the characterization of PEFCs, the nature and extend of the voltage losses at various current densities cannot always be determined without performing time consuming additional experiments, screening various combinations of catalyst coated membranes, operating conditions and even experimental setups3,4. Electrochemical impedance spectroscopy (EIS) on the other hand can give an extensive insight into the nature and extent of voltage loss mechanisms with very fast scan rates without the need to interrupt fuel cell operation9,10 and can therefore accelerate material development efforts. There are however still some unanswered questions about the interpretation of the EIS signals for PEFC.
To address this lack of understanding, we performed an extensive experimental campaign examining the influence of gas pressure, gas relative humidity, gas flow rate, catalyst layer ionomer content and catalyst layer thickness. Thereby, the impact of reactant concentration, water concentration, supply and removal of reactants and products to and from the active sites is quantified. These are all processes that can be seen in the impedance spectrum. By variation of the controlling parameters a better understanding of the spectrum can be obtained. We continued the experimental and empirical modelling work based on previously published work that was mainly concerned with the influence of catalyst layer thickness and ionomer content9 and added important experimental data from a variation of operating conditions. In the present work, we delve deeper in the experimental results obtained and present an equivalent circuit model that facilitates EIS data interpretation.
Original language | English |
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Pages | 52 |
Number of pages | 1 |
DOIs | |
Publication status | Published - Jul 2022 |
Event | 8th Regional Symposium on Electrochemistry of South-East Europe and 9th Kurt Schwabe Symposium: RSE-SEE 2022 - TU Graz, Graz, Austria Duration: 11 Jul 2022 → 15 Jul 2022 Conference number: 8 |
Conference
Conference | 8th Regional Symposium on Electrochemistry of South-East Europe and 9th Kurt Schwabe Symposium |
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Abbreviated title | RSE-SEE 2022 |
Country/Territory | Austria |
City | Graz |
Period | 11/07/22 → 15/07/22 |
Keywords
- fuel cell
- MEA
- material
- production