Polymer electrolyte membrane (PEM) fuel cells are promising alternative green power source for mobile, portable and stationary applications. However, their cost, durability, and performance are impacted by their sensitivity to impurities in fuel stream. Carbon monoxide (CO), an impurity commonly present in the hydrogen gas produced from hydrocarbon fuels, is known to have a significant degrading effect on PEM fuel cell performance because CO has a strong affinity to the platinum-based catalyst. At present, most studies in literature are limited to either experimental or simplified-dimensional analysis/modeling. In this thesis research, a three-dimensional (3D) multiphase PEM fuel cell model with the CO poisoning and O2 bleeding is developed based on the conservation laws for mass, momentum, energy, and species, and implemented in the commercial software Fluent (6.3.26) through the user-defined functions. Numerical simulations are conducted to simulate a single PEM fuel cell including flow channels, gas diffusion layers, catalyst layers, and PEM. The simulation results are compared with experimental data favorably. The result shows that the reaction rate of hydrogen in the anode catalyst layer is higher near the membrane layer, decreasing towards the gas diffusion layer (GDL) interface, and the reaction rate in general is higher in the inlet region and decreases towards the exit region of the flow channel. It means that the outlet of anode catalyst layer next to the flow channel and GDL has suffered the most significant poisoning effect. The result helps optimize the design of anode catalyst layer by embedding more platinum on the most poisoned area to increase available surface for hydrogen adsorption; similarly, reducing platinum loading on the less poisoned area. The fuel cell performance can be almost fully recovered when switching the anode fuel mixture to pure hydrogen, though it takes a long period of time. The reaction rate of hydrogen decreases significantly along the flow channel when impurity mixture is provided; while there is little change along the channel for pure hydrogen fuel. Adding oxygen into the anode fuel mixture can mitigate CO poisoning, but there is a time delay when the oxygen is introduced into the anode stream and when the performance starts to recover. It is observed that at the beginning of oxygen introduced in the anode stream the recovery rate in the region adjacent to the channel outlet is faster than the rate in the region close to the inlet. This difference in the recovery rate gradually becomes smaller over time. In addition, the influence of CO poisoning and oxygen bleeding on multi-phase water is investigated. The influence on dissolved water is only clearly seen in the anode catalyst layer next to the land area. Finally, response to sudden load changes is simulated by changing cell voltage. It is found that the overshoot and undershoot are more significant at high current densities.

Non-woven carbon paper is a porous material composed of carbon composite and is the preferred material for use as the gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells. This material is both chemically and mechanically stable and provides a free path for diffusion of reactants and removal of products and is electrically conductive for transport of electrons. The transport of species in the GDL has a direct effect on the overall reaction rate in the catalyst layer. Numerical simulation of these transport phenomena is dependent on the transport properties associated with each phenomenon. Most of the available correlations in literature for these properties have been formulated for spherical shell porous media, sand and rock, which are not representative of the structure of the GDL. Hence, the objective of this research work is to investigate the transport properties (diffusion coefficient, thermal conductivity, electrical conductivity, intrinsic and relative permeability and the capillary pressure) of the GDL using experimental and numerical techniques. In this thesis, a three-dimensional reconstruction of the complex, anisotropic structure of the GDL based on stochastic models is used to estimate its transport properties. To establish the validity of the numerical results, an extensive comparison is carried out against published and measured experimental data. It was found that the existing theoretical models result in inaccurate estimation of the transport properties, especially in neglecting the anisotropic nature of the layer. Due to the structure of the carbon paper GDL, it was found that the value of the transport properties in the in-plane direction are much higher than that in the through-plane direction. In the in-plane direction, the fibers are aligned in a more structured manner; hence, the resistance to mass transport is reduced. Based on the numerical results presented in this thesis, correlations of the transport properties are developed. Further, the structure of the carbon paper GDL is investigated using the method of standard porosimetry. The addition of Teflon was found have little effect on the overall pore volume at a pore radius of less than 3 micro meters. A transition region where the pore volume increased with the increase in pore radius was found to occur for a pore radius in the range 3<5.5 micro meters regardless of the PTFE content. Finally, the reduction of the overall pore volume was found to be proportional to the PTFE content. The diffusion coefficient is also measured in this thesis using a Loschmidt cell. The effect of temperature and PTFE loading on the overall diffusibility is examined. It was found that the temperature does not have an effect on the overall diffusibility of the GDL. This implies that the structure of the GDL is the main contributor to the resistance to gas diffusion in the GDL. A comparison between the measured diffusibility and that predicted by the existing available models in literature indicate that these models overpredict the diffusion coefficient of the GDL significantly. Finally, both the in-plane and through-plane thermal conductivity were measured using the method of monotonous heating. This method is a quasi-steady method; hence, it allows the measurement to be carried out for a wide range of temperatures. With this method, the phase transformation due to the presence of PTFE in the samples was investigated. Further, it was found that the through-plane thermal conductivity is much lower than its in-plane counterpart and has a different dependency on the temperature. Detailed investigation of the dependency of the thermal conductivity on the temperature suggests that the thermal expansion in the through-plane direction is positive while it is negative in the in-plane direction. This is an important finding in that it assists in further understanding of the structure of the carbon paper GDL. Finally, the thermal resistance in the through-plane direction due to fiber stacking was investigated and was shown to be dependent on both the temperature and compression pressure.

A single polymer electrolyte membrane fuel cell (PEMFC) is comprised of several sub-millimetre thick layers of varying porosity sandwiched together. The thickness of each layer, which typically ranges from 10 to 200μm, is kept small in order to minimize the transport resistance of heat, mass, electrons, and protons, that limit reaction rate. However, the thickness of these materials presents a significant challenge to engineers characterizing the transport properties through them, which is of considerable importance to the development and optimization of fuel cells. The objective of this research is to address the challenges associated with measuring the heat conduction and gas diffusion transport properties of thin porous media used in PEMFCs. An improvement in the accuracy of the guarded heat flow technique for measuring thermal conductivity and the modified Loschmidt Cell technique for measuring gas diffusivity are presented for porous media with a sub-millimetre thickness. The improvement in accuracy is achieved by analyzing parameters in each apparatus that are sensitive to measurement error and have the largest contribution to measurement uncertainty, and then developing ways to minimize the error. The experimental apparatuses are used to investigate the transport properties of the gas diffusion layer (GDL) and the microporous layer (MPL), while the methods would also be useful in the study of the catalyst layer (CL). Gas diffusion through porous media is critical for the high current density operation of a PEMFC, where the electrochemical reaction becomes rate-limited by the diffusive flux of reactants reaching reaction sites. However, geometric models that predict diffusivity of the GDL have been identified as inaccurate in current literature. Experimental results give a better estimate of diffusivity, but published works to date have been limited by high measurement uncertainty. In this thesis, the effective diffusivity of various GDLs are measured using a modified Loschmidt cell and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for predicting diffusivity as a function of porosity in the through-plane direction of a GDL. The thermal conductivity and contact resistance of porous media are important for accurate thermal analysis of a fuel cell, especially at high current densities where the heat flux becomes large. In this thesis, the effective through-plane thermal conductivity and contact resistance of the GDL and MPL are measured. GDL samples with and without a MPL and coated with 30%-wt. PTFE are measured using the guarded steady-state heat flow technique described in the ASTM standard E 1225-04. Thermal contact resistance of the MPL with the iron clamping surface was found to be negligible, owing to the high surface contact area. Thermal conductivity and thickness of the MPL remained constant for compression pressures up to 15bar at 0.30W/m°K and 55μm, respectively. The thermal conductivity of the GDL substrate containing 30%−wt. PTFE varied from 0.30 to 0.56W/m°K as compression was increased from 4 to 15bar. As a result, the GDL contain- ing MPL had a lower effective thermal conductivity at high compression than the GDL without MPL. At low compression, differences were negligible. The constant thickness of the MPL suggests that the porosity, as well as heat and mass transport properties, remain independent of the inhomogeneous compression by the bipolar plate. Despite the low effective thermal conductivity of the MPL, thermal performance of the GDL can be improved by exploiting the excellent surface contact resistance of the MPL while minimizing its thickness.

In the study, micro-PEM fuel cells are designed and fabricated in-house through a deep UV lithography SU-8 process and a wet etching technique for perforated holes plates (diameter is 750 £gm) of 50 £gm thickness of pure copper. Measurements of cell performance are performed using the low percentage of the weight concentration (1-10 wt. %) of NaOH solution, Al paper as the source material for hydrogen production, and different open ratios of the perforated plates to determine which best improves cell power density. Experimental results are presented in the form of polarization VI and PI curves under the above operating conditions. The experimental results show cell performance is enhanced by the self-heating, humidifying of hydrogen production, hydrogen internal circulation and accumulated pressure. Finally, the micro-PEM fuel cell system with DC/DC boost converter can generate 4.99 V for use in cellular phone accumulators charging.

Fuel cells are the tools which convert chemical energy into electricity directly by the effective utilization of hydrogen and oxygen (or air). One of the most important barriers for the fuel cell commercialization is the durability of the fuel cell components in the long term operations. In this study, the durability of the PEM fuel cell electrocatalysts were investigated via cyclic voltammetry (CV) and rotating disk electrode (RDE) experiments in order to determine the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) which corresponds to the half cell reactions in the fuel cell. PEM fuel cell electrodes mainly composed of carbon supported Pt catalysts. In long term operations due to Pt dissolution and carbon corrosion some properties of the electrocatalysts can be changed. Performance losses in catalysts mainly depend on / i) decrease in the total metal surface area (SA) and the electrochemically active surface area (ESA) due to the increase in the particle size ii) decrease in the tafel slope potential in ORR and iii) increase in carbon corrosion. In this study, these properties were examined via accelerated degradation tests performed in CV and RDE. The catalysts having different Pt loadings, synthesized with different ink compositions, pH values and microwave durations were investigated. The commercial catalysts having Pt loadings of 20, 50 and 70 (wt %) were tried and best results were obtained for Pt/V (50 wt %) catalyst. Different carbon to Nafion&reg / ratios of 4, 8, 12 in the ink composition were tried. C/N ratio of 8 gave the best result in Pt dissolution and carbon corrosion degradation tests. The catalysts prepared at different pH values of 1.4, 6.25 and 10 were tried and the catalyst prepared at pH of 10 was less degraded in Pt dissolution test and the catalyst prepared at pH of 6.25 showed better resistance to carbon corrosion. Catalysts prepared under different microwave durations of 50, 60 and 120 s were tried and the catalyst prepared at 60 s gave the best performances.

In this study a three-dimensional mathematical model is developed to simulate the flow field and mass transfer in a PEM fuel cell. In the model, the effects of the different flow channel structures in heterogeneous composite carbon fiber bipolar plates and traditional hard surface bipolar plates on the performance are studied. The results show that, the cell performance with the heterogeneous composite carbon fiber bipolar plates have better performance than that with the traditional hard surface bipolar plates, whether in the parallel flow channel structures or the serpentine flow channel structures. The reason is that, the heterogeneous composite carbon fiber ribs are porous material, so it allows the reactants and products transport uniformly even in the rib zone. This greatly improved the mass transfer and the gases distribution in the fuel cell. With the traditional bipolar plates, the reactants can only enter the reaction zone from the side of carbon cloth under ribs, so that the performance in this area under rib is relatively poor. In the simulation of the flow channel structures, we detect that, due to the single inlet serpentine flow channel have stronger convective effects that forced reactants to flow through the whole reaction zones, so it has better performance at high current density than in the singles inlet parallel flow channel. In addition, the results also show that, higher fuel stoichiometric number and operated pressure and properly humidified at anode will all improve the performance of the fuel cell.

The design and method of cell assembly plays an important role in the performance of PEM fuel cell. The cell assembly will affect the contact behavior between the bipolar plates, flow-channel plates, gas diffusion layers (GDLs) and membrane electrode assembly (MEA). From the past studies, it was noted that the flow-channel plates in the cell will be deformed while the cell was assembled by locking with bolts. This phenomenon may lead to leakage of fuels, high contact resistance and malfunctioning of the cells. The main aim of this research is to study the variation of the deformation mode of the flow-channel plat in a micro-PEM fuel cell assembly subjected to different bolts locking sequences. The commercial FEM package, ANSYS, was adopted to model the three-dimensional single micro-PEMFC FEM model and the numerical simulation analyses were performed. The effect of the bolts locking sequence on the deformations of flow-channel plate in the micro-PEMFC was presented. A most properly bolts locking sequence was proposed also.

<p>Vehicles powered by proton exchange membrane (PEM) fuelcells are approaching commercialisation. Being inherently cleanand efficient sources of power, fuel cells constitute asustainable alternative to internal combustion engines to meetfuture low-emission legislation. The PEM fuel cell may befuelled directly by hydrogen, but other alternatives appearmore attractive at present, due to problems related to theproduction, transportation and handling of hydrogen.</p><p>Fuelling with an alcohol fuel, such as methanol, which isoxidised directly at the anode, offers certain advantages.However, the efficiency of the direct-methanol fuel cell (DMFC)is still significantly lower than that of the conventionalhydrogen-fuelled PEM fuel cell, due to some technical problemsremaining unsolved. Hence, indirect fuelling by a reformedliquid fuel may be the most feasible option in the early stagesof the introduction of fuel cell vehicles.</p><p>The work presented in this thesis concerns the developmentof catalysts for production of hydrogen from methanol bypartial oxidation, steam reforming or a combination thereof.The work contributes to the understanding of how thepreparation route affects catalyst morphology and howphysicochemical properties determine catalytic behaviour andreaction pathways.</p><p>The thesis is a summary of seven papers published inscientific periodicals. The first paper (Paper I) reviews thecurrent status of catalytic hydrogen generation from methanol,focusing on the fuel cell application. Paper II investigatesthe partial oxidation of methanol over Cu/ZnO catalystsprepared in microemulsion and by a conventionalco-precipitation technique. The activity for methanolconversion in the low-temperature regime is found to besignificantly higher over the former materials and the workcontinues by determining the nature of possible Cu-ZnOinteractions in the catalysts by studying their physicochemicalproperties more thoroughly (Paper III). In Paper IV, thepathways for methanol conversion via both partial oxidation andsteam reforming are elucidated.</p><p>In Paper V, partial oxidation of methanol is studied overPd/ZnO catalysts prepared by microemulsion technique and againcompared to conventional materials. This investigationdemonstrates that although possessing high methanol conversionactivity, palladium-based catalysts are not suitable forreforming in fuel cell applications due to the considerableamounts of carbon monoxide formed.</p><p>In Paper VI, methanol reforming is investigated over acommercial Cu/ZnO/Al2O3 catalyst. The mechanisms for carbonmonoxide formation and strategies for its suppression arediscussed, as well as reactor design aspects. The study alsoincludes some simple kinetic modelling. Finally, Paper VIIdescribes the optimisation of catalyst composition and processconditions to reach high hydrogen production efficiency at lowoperating temperatures and with minimum carbon monoxideformation.</p><p><b>Keywords:</b>PEM fuel cells, hydrogen, methanol, reforming,(partial) oxidation, reaction pathways, carbon monoxide,catalyst, microemulsion, Cu/ZnO, Pd/ZnO, copper, redoxproperties, oxidation state</p>

Fuel cells are electrochemical energy devices that convert the chemical energy in a fuel into electrical energy. Although they are more efficient, clean, and reliable than fossil fuel combustion systems, they have not been widely adopted because of manufacturing challenges and high production cost. The most expensive component of a fuel cell is the membrane electrode assembly (MEA), which consists of an ionomer membrane coated with catalyst material. Best performing MEAs are currently fabricated by depositing and drying liquid catalyst ink on the membrane, however, this process is limited to individual preparation by hand due to the membrane’s rapid water absorption that leads to shape deformation and coating defects. This work models the swelling and drying phenomena of the membrane and coating during manufacturing, and then applies the results to develop and control a continuous coating line for the production of defect free fuel cell MEAs. A continuous coating line can reduce the costs and time needed to fabricate the MEA, incentivizing the commercialization and widespread adoption of fuel cells. Membrane swelling is a three-dimensional, transient, coupled mass transfer, heat transfer, and solid mechanics problem. Existing models describe the membrane’s behavior in operating conditions, but none predict the behavior during manufacturing. This work develops a novel physics-based model that describes the behavior of the membrane and coating in a continuous manufacturing scenario and incorporates effects that are missing from existing models. A model that can predict wrinkles, the most commonly observed defect during manufacturing, is presented. Simulation results from the above models are used to design and develop an improved continuous MEA coating process that includes pre-swelling and two-stage drying of the coated membrane. A prototype pilot-scale coating line to implement and test the improved coating process is designed and constructed. Finally, a Linear-Quadratic-Gaussian type controller is developed using the physics-based model of the manufacturing process to optimally control the temperature and humidity of the drying zones, and its effectiveness when implemented on the coating line is discussed. / text

The objective of this study is to shed more light on the electrochemical interface of HTPEM fuel cell. More specifically, to understand and improve the electrochemical interface of both the anodic and cathodic electrode in HTPEM fuel cells, as well as optimize the catalyst layer structure for operation under various challenging conditions. For that reason the effect of the PA amount in the catalyst layer and the effect of the catalyst’s substrate on the fuel cell’s performance were investigated. Initially the poisoning effect of PA on the anodic electrode was investigated. The PA amount was altered in the anodic catalyst layer and its effect on the ECSA and the anode’s performance were evaluated. It was observed that the reversible performance loss of the anodic electrode was a function of the PA amount in the catalyst layer. More specifically, under low PA loading (<3 gPA/gPt) on the anodic electrode, < 10% of the Pt active surface is electrochemically active under fuel cell operating conditions. This was attributed to the blockage of the Pt surface by pyrophosphoric acid or poly-phosphates, H2 reduced polyphosphoric acid species and the shrinkage of the interface due to the displacement of the H3PO4 by the adsorbed H2 species. High PA loadings reduced the poisoning effect of these reduced PA species ( >3 gPA/gPt). It was found that the controlled and increased PA content within the catalytic layer can result even up to the tenfold decrease in the Pt loading when the anode operates under H2 rich conditions. In order to increase the fuel cell performance and increase the three phase boundary, a newly synthesized electrocatalyst was evaluated, and compared to the commercial 30wt%Pt/C. The new catalyst is based on pyridine functionalized carbon nanotubes ,30wt%Pt/oxMWCNT-Py. Pyridine groups are known to interact with PA and thus it is expected to increase the TPB and lower the Pt loading. CL employing the new catalyst were formulated and tested at the anodes. It was found that the presence of pyridine groups homogeneously distributed PA in the catalyst layer, resulting in high ECSA values, 40m2/gPt. As a result the MEA employing 30wt% Pt oxMWCNT-Py showed the same performance as the 30%Pt/C (having 1.3mgPt/cm2), for Pt loading loadings as low as 0.2mgPt/cm2. The performance of the anodic electrode was also found to be largely depended on the PA amount imbedded in the CL, when low Pt loading were used. The latter was an effect of the shrinkage of the ECSA as a result of the formation of PA poisoning species, as also mentioned in the previous paragraph. Since 30wt% Pt/oxMWCNT-Py exhibited very promising results and high ECSA values, its performance under harsh synthetic reformate gas was also evaluated. The synthetic reformate gas that was used comprised of 50.7kPa of H2, 2 kPa of CO and 33.5kPa of H2O balanced with Ar. It was found that the 30wt%Pt/oxMWCNT-Py electrocatalyst are ideal candidates for operation under those harsh reformates conditions, as they exhibited smaller voltage losses and higher stability under these conditions. The interaction of pyridine groups with phosphoric acid not only promotes its uniform distribution on the CL but also stabilizes the EI under high partial pressure of water. Additionally, the use of pyridine functionalized MWCNT based electrocatalyst gives the opportunity of lowering the Pt loading in the electrodes without sacrificing the overall cell’s performance under reformate conditions. The observed voltage loss under synthetic reformate gas rich in CO and steam was found to be a multi-step process and a function of the hydrophobicity of catalyst substrate, the PA loading in the CL as well as the water and CO molar fraction in the reformate gas. In order to optimize the cathodic catalyst layer, CL were formulated using the newly synthesized electrocatalyst (30wt%Pt/oxMWCNT-Py) and compared to the commercial 30wt%Pt/C. A full parametric analysis with respect to catalyst type, PA loading and Pt loading was conducted. It was found that the presence of pyridine groups homogeneously distributes PA in the catalyst layer minimizing the blockage of the pores of the catalyst layer and increase the three phase boundary. As a result the MEA employing 30wt% Pt oxMWCNT-Py showed the same performance as the 30%Pt/C for half the Pt loading. Despite the hard operating conditions the Pt particles attached to the ox.MWCNT-Py substrate exhibit the same stability as the commercial catalyst and the pyridine groups were found to be stable, at least for short term operation at the cathodic and anodic electrode. Also optimization of the ECSA evaluation procedure at the cathodic electrode, using CO as a probe molecule, without damaging the Pt distribution was found. It is clear that the use of this newly synthesized electrocatalyts 30wt%Pt/oxMWCNT-Py , at both electrodes, has major advantages as it increase the catalyst utilization and there is no need to use a polymer-binder inside the catalytic layer. Thus avoiding problems of inhomogeneous binder distribution and/or electronic insulation of catalyst nanoparticles. Using 30wt%Pt/oxMWCNT-Py electrocatalyst opens the possibility of significant reduction of the amount of Pt on both electrodes, under various operation conditions, without sacrificing the performance and stability of the fuel cell. / Στο πλαίσιο της παρούσας διδακτορικής διατριβής έγινε σύνθεση ενός νέου βελτιωμένου ηλεκτροκαταλύτη Pt για χρήση σε κελιά καυσίμου πολυμερικής μεμβράνης υψηλών θερμοκρασιών (HTPEM), με σκοπό την αύξηση της ηλεκτροχημικά ενεργού επιφάνειας τόσο του ανοδικού όσο του καθοδικού ηλεκτροδίου. Ο καταλύτης αυτός αποτελείται από 30 % κ.β. Pt σε φορέα τροποποιημένους πολυ-φλοιϊκούς νανοσωλήνες άνθρακα (MWCNT). Οι νανοσωλήνες άνθρακα τροποποιήθηκαν σταδιακά, σε ένα πρώτο βήμα με ομάδες οξυγόνου (ox.MWCNT) και στη συνέχεια με ομάδες πυριδίνης (ox.MWCNT-Py) που προσαρτήθηκαν μέσω ομοιοπολικών δεσμών στο εξωτερικό τοίχωμά τους, ώστε να επιτευχθεί ομοιόμορφη κατανομή τους στο καταλυτικό στρώμα. Επειδή οι ομάδες πυριδίνης (Py) δεσμεύουν το φωσφορικό οξύ, το οποίο χρησιμοποιείται ως ιοντικός αγωγός, δημιουργείται ένας ιοντικά αγώγιμος δρόμος κατά μήκος του καταλυτικού στρώματος, με συνακόλουθη αύξηση της ηλεκτροχημικά ενεργού επιφάνειας, η οποία επέτρεψε τη σημαντική μείωση της ποσότητας Pt στα ηλεκτρόδια, χωρίς μείωση της απόδοσης και σταθερότητας του κελιού καυσίμου. Πλεονέκτημα αυτής της προσέγγισης για αύξηση της απόδοσης του ηλεκτροκαταλύτη Pt είναι το ότι αποφεύγεται η χρήση ενός ιονομερούς στο εσωτερικό του καταλυτικού στρώματος και τα προβλήματα που σχετίζονται με την ανομοιογενή κατανομή του. Εξετάστηκαν επίσης η επίδραση στην απόδοση του ανοδικού ηλεκτροδίου της παρουσίας CO και υψηλής μερικής πίεσης υδρατμού στην τροφοδοσία της ανόδου, στη περίπτωση χρήσης αερίου αναμόρφωσης ως καυσίμου. Για διερεύνηση του μηχανισμού ανάπτυξης υπέρτασης (ενεργειακής απώλειας σε όρους δυναμικού) στη περίπτωση αυτή και βελτιστοποίηση της λειτουργίας του κελιού καυσίμου, παρασκευάστηκαν ηλεκτρόδια με χρήση τριών διαφορετικών καταλυτών Pt, συγκεκριμένα των καταλυτών 30% κ.β. Pt/C, 30% κ.β. /oxMWCNT και 30wt%Pt/oxMWCNT-Py. Τα ηλεκτρόδια αυτά διέφεραν επίσης όσον αφορά στη ποσότητα καταλύτη ανά μονάδα επιφάνειας ηλεκτροδίου και στη ποσότητα φωσφορικού οξέος (PA) στο καταλυτικό στρώμα ανά μονάδα μάζας Pt (0.5 gPA/gPt και 2 gPA/gPt). Η ανάπτυξη υπέρτασης στις αναφερθείσες συνθήκες λειτουργίας αποδόθηκε σε ένα μηχανισμό πολλών σταδίων, ο οποίος βασίζεται στη μείωση της ηλεκτροχημικά ενεργού επιφάνειας λόγω της εκτόπισης του φωσφορικού οξέος από την ηλεκτροχημική διεπιφάνεια. Παρότι το φωσφορικό οξύ αποτελεί ιδανικό αγωγό ιόντων για τα κελιά καυσίμου υψηλών θερμοκρασιών τύπου PEM, παρουσιάζει διάφορους περιορισμούς, όπως το φαινόμενο δηλητηρίασης του ανοδικού ηλεκτροδίου εξαιτίας του, το οποίο επίσης μελετήθηκε στη διατριβή αυτή. Διαπιστώθηκε ότι η αναστρέψιμη απώλεια της απόδοσης του ανοδικού ηλεκτροδίου ήταν συνάρτηση της ποσότητας του H3PO4 στο καταλυτικό στρώμα.