Role of the microporous layer in the redistribution of phosphoric acid in high temperature PEM fuel cell gas diffusion electrodes

Chevalier, S.; Fazeli, Mohammadreza; Mack, Florian; Galbiati, Samuele; Manke, Ingo; Bazylak, Aimy; Zeis, Roswitha

doi:10.1016/j.electacta.2016.06.121

Cited by 43 publications

(23 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The resolution of the m-CT is deficient to determine nanopores in the microporous and catalyst layers (MPL and CL, respectively), but still the cracks could be observed and compared with previous studies [23] in the same resolution range, the CLs presented in this work are relatively defect-free. In such a way, mass and charger transfer deterioration observed in both fuel switching tests and detected with EIS investigations could be related to the cracks identified in the CLs.…”

Section: Fuel Switchingmentioning

confidence: 71%

See 1 more Smart Citation

Long‐term Operation of High Temperature Polymer Electrolyte Membrane Fuel Cells with Fuel Composition Switching and Oxygen Enrichment

et al. 2018

View full text Add to dashboard Cite

The performance of commercially available High temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) cells was electrochemically (impedance spectroscopy, polarization curves, performance over time) and optically characterized ante and post mortem via micro‐computed tomography. Investigations on the performance gain, due to oxygen enrichment of cathode air and the capabilities of the commercial MEAs to switch and operate between pure hydrogen and synthetic dry reformate (78% H2 and 22% CO2), were carried out. Two experiments at constant load conditions were performed, Cycle 1 consisted of 12 h pure hydrogen operation followed by 12 h of synthetic reformate, while Cycle 2 was operated with 1 h of H2 followed by 5 h of synthetic reformate. The results revealed that oxygen enrichment improves mass transport from the gas flow channels to the cathode catalyst layer as well as catalyst utilization. Thus, oxygen concentration increase from 21% (air) to 30% at 0.3 A cm−2 developed a performance improvement of roughly 8%. Only marginally influence on fuel cell performance and degradation was observed in fuel switching experiments. A content of 22% CO2 had little influence on degradation, which could mainly be related to fuel dilution. Besides, micro‐computed tomography (µ‐CT) investigations revealed similar membrane and catalyst layer degradation for both kinds of fuel switching tests.

show abstract

Section: Fuel Switchingmentioning

confidence: 71%

“…The resolution of the μ‐CT is deficient to determine nano‐pores in the microporous and catalyst layers (MPL and CL, respectively), but still the cracks could be observed and compared with previous studies in the same resolution range, the CLs presented in this work are relatively defect‐free.…”

Section: Resultsmentioning

confidence: 99%

Long‐term Operation of High Temperature Polymer Electrolyte Membrane Fuel Cells with Fuel Composition Switching and Oxygen Enrichment

et al. 2018

View full text Add to dashboard Cite

show abstract

“…5,7,10,11 The accumulated acid is probably dispersed across large parts of the anode (and MPL/GDL). [5][6][7] This will presumably encourage its loss from the cell, e.g., via a combination of evaporation, surface diffusion, and possibly even dislodging of acid droplets. In a similar fashion, any hydronium cations that migrate to the cathode will be reduced upon reaching their destination, causing electroosmotic water drag and accumulation of water in that region.…”

Section: Resultsmentioning

confidence: 99%

“…[5][6][7] As reviewed by Jakobsen et al, a number of mechanisms have been proposed to explain the loss of doping-acid from PBI membranes, including evaporation into the gas phase and a so-called steam distillation mechanism, the latter of which has been proposed governed by temperature as well as humidity. 9 Migration of electrolyte ions might also be an issue with respect to acid loss, particularly if the proton transference number deviates significantly from the maximum value for phosphoric acid (ca.…”

mentioning

confidence: 99%

Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Søndergaard

Cleemann

Becker

et al. 2018

J. Electrochem. Soc.

View full text Add to dashboard Cite

This work studies the long-term durability of high-temperature polymer electrolyte membrane fuel cells based on acid-doped polybenzimidazole membranes. The primary focus is on acid loss via the evaporation mechanism, which is a major cause of degradation in applications that involve long-term operation. Durability is assessed for 16 identically fabricated membrane electrode assemblies (MEAs), and evaluations are carried out using operating parameters as stressors with gas stoichiometries ranging from 2 to 25, current densities from 200 to 800 mA cm −2 , and temperatures of 160 or 180 • C. Cell diagnostics are composed of time resolved polarization curves, post mortem analysis, and in situ temperature measurements. A major part of the cell degradation during these steady-state tests can be ascribed to increasing area-specific series resistance. By means of post mortem acid-loss measurements, the degradation is correlated to the temperature and to the accumulated gas-flow volume. Such relations are indicative of acid loss via evaporation. Current density also plays a critical role for the acid loss and, thus, for the overall cell degradation. The effect of current is likely tied to mechanisms that involve water generation, migration of electrolyte ions, and locally elevated temperature inside the Since the polybenzimidazole (PBI) polymer acts as a Brønsted base in relation to phosphoric acid, membranes of PBI can be doped with phosphoric acid through acid-base complexation. Some of the H 3 PO 4 molecules, 2 per polymer repeat unit, are then bound to the basic functional sites of the polymer. However, excess acid is essential in order to attain a conductivity that is high enough for use as electrolyte in a polymer electrolyte membrane fuel cell (PEMFC). Fuel cells based on this type of electrolyte are known as high-temperature (HT-)PEMFCs, typically operating at temperatures of 140-180• C. Phosphoric acid-doped PBI membranes can be prepared either by direct (or so-called sol-gel) casting from a solution of PBI dissolved in polyphosphoric acid (PPA) or by solution casting of a PBI film via solvent evaporation, for which acid-doping follows subsequently. 1 For HT-PEMFCs, the cell performance usually increases to a stable state within the first few hundred hours of operation. This activation of the cell might be a consequence of acid redistribution in the membrane electrode assembly (MEA).2-4 Such redistribution of acid also implies susceptibility to its loss, however, because it is a testament to the mobility of the doping-acid. [5][6][7] As reviewed by Jakobsen et al., a number of mechanisms have been proposed to explain the loss of doping-acid from PBI membranes, including evaporation into the gas phase and a so-called steam distillation mechanism, the latter of which has been proposed governed by temperature as well as humidity. 9 Migration of electrolyte ions might also be an issue with respect to acid loss, particularly if the proton transference number deviates significantly from the maximum value for phosphori...

show abstract

“…It was found that the presence of an MPL improves the adhesion between catalyst layer and GDL and is beneficial to the performance of HT‐PEMFCs. Recent work of Chevalier et al was based on the Freudenberg H23C2 product, a GDL with an MPL made of non‐woven carbon cloth. It was clearly shown that at the catalyst layer/MPL interface there were cracks, through which the PA invasion into the GDL occurs.…”

Section: Introductionmentioning

confidence: 99%

Acid Distribution and Durability of HT‐PEM Fuel Cells with Different Electrode Supports

Kannan

Cleemann

et al. 2018

Fuel Cells

View full text Add to dashboard Cite

The durability of high‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) was studied with phosphoric acid doped membranes of polybenzimidazole (PBI). One of the challenges for this technology is the loss and instability of phosphoric acid resulting in performance degradation after long‐term operation. The effect of the gas diffusion layers (GDL) on acid loss was studied. Four different commercially available GDLs were subjected to passive ex situ acid uptake by capillary forces and the acid distribution mapped over the cross‐section. Materials with an apparent fine structure made from carbon black took up much more acid than materials with a more coarse apparent structure made from graphitized carbon. The same trend was evident from thermally accelerated fuel cell tests at 180 °C under constant load where degradation rates depended strongly on the choice of GDL material, especially on the cathode side. Acid was collected from the fuel cell exhaust at rates clearly correlated to the fuel cell degradation rates, but amounted to less than 6% of the total acid content in the cell even after significant degradation. Long‐term durability of more than 5,500 h with a degradation rate of 12 µV h−1 at 180 °C and 200 mA cm−2 was demonstrated with the GDL that retained acid most efficiently.

show abstract

Role of the microporous layer in the redistribution of phosphoric acid in high temperature PEM fuel cell gas diffusion electrodes

Cited by 43 publications

References 55 publications

Long‐term Operation of High Temperature Polymer Electrolyte Membrane Fuel Cells with Fuel Composition Switching and Oxygen Enrichment

Long‐term Operation of High Temperature Polymer Electrolyte Membrane Fuel Cells with Fuel Composition Switching and Oxygen Enrichment

Long-Term Durability of PBI-Based HT-PEM Fuel Cells: Effect of Operating Parameters

Acid Distribution and Durability of HT‐PEM Fuel Cells with Different Electrode Supports

Contact Info

Product

Resources

About