Polymer exchange membrane fuel cells (PEMFCs) are promising energy converters due to their unique features with an application potential for many sectors. The performance of PEM fuel cells depends on a number of factors, one of which is suitable flow‐field design. In this study, the effect of spiral flow‐field design is investigated with computational fluid dynamics (CFD) method. The model consists of the transport phenomena in a fuel cell. Electrochemical reactions, mass, heat, energy, species transport, and potential fields equations are solved by ANSYS‐FLUENT. The polarization and power density curve, temperature, pressure, and distributions of the gases inside the flow‐fields were obtained. The results were compared with the reference geometry. Although the spiral flow‐field has considerable ohmic losses, the velocity and pressure distributions of the gases are found to be uniform. Furthermore, it is shown that the spiral flow‐field reduces the pressure drop per unit length of the flow‐field. When compared to other flow‐field designs, the spiral flow‐field is found to be quite efficient by means of auxiliary power consumption.
HT-PEMFC based on phosphoric acid-doped polybenzimidazole membranes are a technology characterized by simplified construction and operation along with methanol reformers. Durability issues including acid loss, platinum sintering and carbon corrosion are recognized for both steady state and start-stop cycling operations. This work reports experimental studies on the degradation of PBI-based fuel cells operating with synthetic reformate fuel and air. Degradation stressors include elevated temperatures, pressures, current densities, and start-stop cycles. An average degradation rate of 9.3 µV/h is observed for continuous operation at 0.4 A/cm 2 and 160 ˚C for 12,000 h. High pressure (1.5 bar abs ) operation at 170 o C and 0.8 A/cm 2 shows an average degradation rate of 12.6 µV/h during a period of 2,000 h. A startstop test from 50 o C consisting of 240 cycles between temperatures of 165 and 175 o C and current density of 0.31 and 0.55 A/cm 2 reveals a performance decay by 0.48-0.58 mV/cycle.
The performance degradation mechanisms, mitigation strategies and durability protocols of polybenzimidazole-based polymer electrolyte membrane fuel cells are fully reviewed.
Proton exchange membrane fuel cells (PEMFC) look extremely promising as energy conversion solution for both stationary and transportation applications. However, for the further application, durability still needs to be improved in order to compete with the internal combustion engine.1 The present work focuses on ongoing work based on membrane electrode assemblies (MEAs) for high temperature Proton exchange membrane fuel cells (HT-PEMFCs). HT-PEMFCs were operated at 160-170 °C using either pure humidified hydrogen or humidified reformate of different compositions.2 The high operating temperature makes it possible to operate commercial fuel cell systems using methanol (or methanol-water mixtures) as fuel. The HT-PEM cells can tolerate fuel impurities e.g. up to 3 vol-% CO and 20 ppm H2S without significant performance losses, which could lead to higher operating efficiency.Our studies have shown remarkable durability of an HT-PEMFC equipped with a thermally cross-linked m-PBI membrane. A decay rate of only 0.5 μV /h at 0.2 A/cm2 over an extended period of time (9,200 h) was oserved.3 Further, we have illustrated that an increase in the pressure of the in-going gases to 1.5 bar (abs) – as expected – increases the performance. The preliminary results confirmed a power density of 0.5 W/cm2 at 0.9 A/cm2.Continuous operation and more than 260 start stop cycles have been performed in order to study the degradation effects of both continuous operation and of repeated start stops. The durability of HT-PEMFC can now be considered similar to low temperature PEMFC. Graphs of single cell performance during operation have shown very stable behavior for over 10,000 at a current density of 0.4 A/cm2.Several demonstration projects have been made, especially for cars and we continue improving our products (HT-PEMFCs), looking for innovative solutions to current limitations on HT-PEMFC durability. References: Vichard, R. Petrone, F. Harel, A. Ravey, P. Venet, D. Hissel, Energy Convers. Manag, 212 (2020) 112813-112823.O. Jensen, D. Aili, H. A. Hjuler, Q. Li, High Temperature Polymer Electrolyte Membrane Fuel Cells - Approaches, Status and Perspective, ISBN 978-3-319-17081-7; DOI 10.1007/978-3-319-17082-4, Springer International Publishing, New York, 2015.Tonny, D. Jakobsen, L. N. Cleemann, H. Becker, D. Aili, T. Steenberg, H. A. Hjuler, L. Seerup, Q. Li, J.O. Jensen, J. Power Sources, 342 (2017) 570-578.
The commercialization of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) has been limited by (1) their considerable platinum (Pt) loadings, and (2) durability, compared to low temperature PEMFCs (LT-PEMFC). However, the elevated temperature in HT-PEMFC (140 – 160 °C) ensures resilience towards catalytic poisoning from CO (<3%) and H2S (<20 ppm) as fuel impurities and SO2 (<40 ppm) as air pollution. This enables the use of methanol, via reforming, as an affordable and environmentally benign fuel.[1] These temperature-driven advantages have been the force behind the development of the HT-PEMFC technology.We have been optimizing methods and materials to enhance Pt utilization and cell lifetime. Recent results showed cell peak performance >400 mW/cm2 using Pt loadings as low as 0.1 mgPt/cm2, however, with lab scale MEAs operating with pure hydrogen. [1,2] Herein we present efforts to decrease Pt loading while retaining or improving the cell performance on industrial scale (humidified reformate feed). These efforts can be split in two different approaches: (1) the MEA materials optimizations, and (2) MEA fabrication process optimizations. The former focused on studying the MEA onset voltage after the 24 – 48 h cell activation interval, versus the optimal MEA Pt loadings. Efforts to decrease the Pt amounts were expanded to comparing the performances of pure Pt and Pt/Co (Cobalt) -alloyed catalysts. The Pt/Co catalyst was superior towards the oxygen reduction reaction (ORR) as compared to its monometallic counterpart. Additionally, the Pt loading in the MEA was lowered by diluting the catalyst with pristine carbon support particles. The goal was to homogeneously distribute Pt towards the bulk of the catalytic layer (CL) so the phosphoric acid (PA) front, originating from the pressed PA-doped polybenzimidazole (PBI) membrane, does not significantly flood Pt nanoparticles. Increased mass activity was demonstrated for cells in which the Pt/C catalyst was “diluted” by additional carbon particles. The effect is explained by adaptation to a dynamic flooding effect. Furthermore, we demonstrate that a pressure increase of the in-going gases (1.5 BarA) enhanced the operating voltage and the cell showed 500 mW/cm2 at 900 mA/cm2. This entails that for the same performance, the Pt MEA content could be reduced.Additionally, the MEA fabrication processes were optimized with the focus on fine-tuning the (1) hot-pressing conditions and (2) the thermal treatment of the electrodes. The parameter changes affected the cell performance favorably, both qualitatively and quantitatively. By optimizing the MEA fabrication processes, the cells exhibited positive activation trends and up to 50 mV voltage increase.Several demonstration projects have been made for automotive and stationary applications to showcase a new generation of economically more efficient MEAs. References: [1] S. Martin, P. L. Garcia-Ybarra, J. L. Castillo, Ten-fold reduction from the state-of-the-art platinum loading of electrodes prepared by electrosp...
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