Proton exchange membrane fuel cell (PEMFC) electrodes comprise multiple functional components whose interplay critically influences both performance and long-term stability. In this article, the interaction between ionomer and catalyst materials was investigated using electrochemical quartz crystal microbalance with dissipation monitoring, enabling detection of potential-dependent changes in mass and viscoelastic properties. Measurements were conducted on platinum, carbon, and gold electrodes, with and without a Nafion overlayer, in 0.5 M H2SO4 and 0.1 M HClO4. Additionally, a representative catalyst layer (CL) was fabricated by spray-coating PEMFC catalyst ink onto quartz crystals and examined under identical electrochemical conditions. Enhanced hydration of Nafion on a platinum electrode was observed during potential cycling, attributed to electrochemical reactions at the platinum surface, rather than being a direct consequence of the applied potential as this behavior was not observed on crystals with Nafion-covered carbon electrodes. Changes in viscoelastic properties and mass uptake was shown to be influenced by the choice of electrolyte solution, particularly the nature of the anions. Importantly, the response of the spray-coated PEMFC-CL aligns closely with the behavior observed for Nafion-coated planar platinum, validating the simplified model approach and providing deeper insight into ionomer behavior under dynamic fuel cell conditions.

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles and other demanding applications, such as aviation, would be simplified if the stacks could operate above 100 °C instead of the traditional low temperature (LT, up to 80 °C), thereby allowing a reduction in cooling system in size and power. This review offers a comprehensive compilation of experimental studies reported in the literature on PEMFCs operated in the intermediate temperature (IT)-range, here defined as above 80 °C and up to 120 °C, which represented the targeted upper temperature for PEMFCs. Membranes, electrodes and gas diffusion layers for IT-PEMFCs are discussed. Particular attention is paid to polymers in membranes and catalyst layer ionomers. Results from current state-of-the-art perfluorosulfonic acids and alternatives, including hydrocarbon polymers, are evaluated considering their properties and limitations. Further, system benefits and drawbacks of IT- compared to the traditional LT-operation are discussed, such as the interplay between vapour and oxygen pressure, hydrogen crossover and water management. We report on the lack of consistency between ex-situ and in-situ studies and underline the importance of in-situ tests, proposing guidelines to evaluate novel materials. For IT-operation, the development of stable polymers, which are the weakest components of the PEMFCs, is the most urgent challenge. As degradation happens faster at higher temperatures, further long-term tests are needed above 80 °C and accelerated stress tests should be specifically designed for IT-operation according to the polymer chemistries. We conclude that, compared to LT-, IT-operation requires improved materials and additional research.

There is currently a drive to operate proton exchange membrane fuel cells at temperatures above 80 degrees C. To achieve this, all aspects of the fuel cell need to be investigated to ensure that performance and durability are maintained. In this work we systematically investigated carbon corrosion from 70 degrees C to 120 degrees C and 40 and 70 % relative humidity (RH). The investigation was done by cyclic voltammetry up to 1.4 V vs RHE with simultaneous mass spectrometry measurements to quantify the produced carbon dioxide. The obtained results were modelled to differentiate the effects of temperature, water partial pressure and different types of carbon corrosion. The results show that the carbon corrosion is mainly affected by the water partial pressure, which increases exponentially with temperature if RH is kept constant. This explains why an increase of temperature (at constant humidity) and an increase of humidity (at constant temperature) lead to faster corrosion kinetics. With current materials, to contrast the effect of the water partial pressure, the upper cell voltage limit in operation must be lowered. The combination of temperatures above 100 degrees C with high relative humidity at high voltage requires material improvement or additional mitigation strategies to avoid excessive carbon corrosion.

Fuel cells convert energy stored in hydrogen into electricity. As a zero-emission technology, they represent a sustainable alternative to conventional combustion engines, particularly for heavy-duty vehicles. Proton exchange membrane fuel cells (PEMFCs) are used in vehicles and typically operate up to 80 °C. To facilitate the cooling of PEMFCs, slightly rising the operating temperature to the range of 80-120 °C, defined as intermediate temperature (IT), would be desirable.

The aim of the thesis is to electrochemically analyze the impact of IT operation on commercially available PEMFC materials. Results show that increasing the temperature has multiple effects on the cell. Increased ionic conductivity, faster reaction kinetics and reduced mass transport resistance are counteracted by a negative shift of the equilibrium potential, enhanced corrosion of the carbon support, and reduced gas barrier properties. Additionally, if the humidity and the cell pressure are constant, the partial pressure of oxygen is reduced at higher temperature, which limits the cell performance. Finally, a higher temperature leads to faster degradation. The ultimate failure is attributed to the formation of pinholes in the membrane, but the polymer conductivity and the catalyst's electrochemical surface area are also negatively affected. 

Despite a scarcity of comparable data above 80 °C, the main obstacle for IT-PEMFCs is apparently the lack of stable materials. Current state-of-the-art polymers for PEMFCs are based on perfluorosulfonic acid (PFSA), whose sustainability has recently been questioned. Alternatively, fluorine-free hydrocarbon-based polymers investigated here show comparable results up to 100°C, but cannot tolerate operation at 120 °C. More research is needed to further develop sustainable materials and to allow continuous operation of PEMFCs in the intermediate temperature range. 

Bränsleceller omvandlar energin lagrad i vätgas till elektricitet. Som nollemissionsteknik utgör de ett hållbarare alternativ till konventionella förbränningsmotorer. Vätgasens höga energiinnehåll gör dem särskilt lovande för tunga fordon. I fordon används vanligtvis protonledande membranbränsleceller (PEMFC) med en driftstemperatur runt 80 °C. För att underlätta kylningen av PEMFC, vore det önskvärt att kunna använda den vid en något förhöjd temperatur, från 80 till 120 °C, definierad som en mellantemperatur (IT). 

Syftet med avhandlingen är att elektrokemiskt analysera inverkan av IT-drift på kommersiellt tillgängliga PEMFC-material. Resultaten visar att en ökning av temperaturen har flera effekter på cellen: ökad jonledningsförmåga, snabbare reaktionskinetik och minskad masstransportmotstånd motverkas av en negativ förskjutning av jämviktspotentialen, ökad korrosion av katalysatorns bärarkol och försämrade gasbarriäregenskaper hos membranet. Dessutom, om fuktigheten och celltrycket är konstanta, minskar syrepartialtrycket vid högre temperatur, vilket begränsar cellens prestanda. I förlängningen orsakar den förhöjda temperaturen en snabbare nedbrytning av PEMFC som slutligen havererar genom att hål bildas i membranet. Även polymerelektrolytens ledningsförmåga och katalysatorns aktiva yta minskar vid långvarig drift.

Det saknas jämförbara data över 80 °C, men uppenbart är det största hindret för IT-PEMFC bristen på stabila material. Nuvarande polymerelektrolyter för PEMFC är baserade på perfluorsulfonsyra (PFSA), vars miljövänlighet nyligen har ifrågasatts. Alternativa fluorfria kolvätebaserade polymerer som undersökts här visar jämförbara resultat upp till 100 °C, men tolererar inte drift vid 120 °C. Mer forskning behövs för att utveckla hållbara material för att möjliggöra kontinuerlig drift av PEMFC i mellantemperaturintervallet.

To improve the Proton Exchange Membrane Fuel Cells (PEMFCs) suitability for heavy-duty vehicles a higher operating temperature is required. However, a higher operating temperature is often associated with higher degradation rates. In this work we investigate the effects of temperature and load on the degradation of commercial state-of-the-art membrane electrode assemblies (MEAs) operating at intermediate temperatures (IT) between 80 and 120 °C during galvanostatic holds. Thorough electrochemical analysis was made together with transmission electron microscopy and modelling. As expected, a more rapid decrease in performance is observed at an increased operating temperature. The main loss in performance is linked to changes in the membrane and ionomer in the membrane electrode assembly. In particular, the membranes fail due to pinhole formation, resulting in higher hydrogen crossover. It is also seen that the ionomer in the cathode degrades faster at elevated temperatures, and that a lower applied load reduces the rate. Further analysis shows small and similar changes in the electrode thickness and particle sizes for all temperatures. Although an elevated temperature reduces the lifetime of a fuel cell, operation at elevated temperatures for shorter durations can be feasible, but the polymer electrolytes must be designed for higher temperatures.

Improved knowledge on Proton Exchange Membrane Fuel Cell (PEMFC) behaviour in the Intermediate Temperature (IT: 80-120 degrees C) is needed. Here, ionic conductivity and H2 permeability are analysed under H2/N2 using electrochemical impedance spectroscopy, linear sweep voltammetry for three catalyst-coated membranes (CCMs): Nafion HP (reinforced), Nafion 211 (non-reinforced) and a reinforced commercial membrane (RCM, membrane thickness 13 mu m). Multiple relative humidity (RH) levels and pressure configurations are analysed at IT. Results show that ionic conductivity and H2 permeability increase with temperature and RH. However, lower crossover is measured above 100 degrees C and wet conditions due to low H2 partial pressure. The highest crossover is measured with an overpressure on the H2 side which, especially for RCM, suggests possible convection. The membrane reinforcement might reduce the permeability and it decreases the conductivity. Mass spectrometry confirmed that sprayed CCMs suffer from higher crossover than pristine membranes, although the membrane thickness is unchanged.

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 degrees C were possible. In this work, the effect of temperature in the intermediate range of 80-120 degrees C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate oper-ation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium po-tential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity dif-ference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simul-taneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.