Understanding how single-atom site density drives the performance and durability of PGM-free Fe–N–C cathodes in anion exchange membrane fuel cells

Adabi, Horie; Santori, Pietro Giovanni; Shakouri, Abolfazl; Peng, Xiong; Yassin, Karam; Rasin, Igal G.; Brandon, Simon; Dekel, Dario R.; Hassan, Noor Ul; Sougrati, Moulay Tahar; Zitolo, Andrea; Varcoe, John R.; Regalbuto, John R.; Jaouen, Frédéric; Mustain, William E.

doi:10.1016/j.mtadv.2021.100179

Cited by 29 publications

(40 citation statements)

References 76 publications

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“…For Fe0.5, they are in good qualitative agreement with the reported decrease of the amount of FeNxCy sites and the concomitant increase of Feoxides, as observed by 57 Fe Mössbauer spectroscopy on another Fe-N-C material based on singleatom-sites, before/after a 100 h durability test at 600 mA cm -2 in air/H2 AEMFC. [68] We also stress that while the reprecipitation of Fe as Fe oxide during AST was quantitatively limited for Fe0.5 in liquid alkaline electrolyte, the outcome in an ionomeric environment free of support liquid electrolyte (stronger increase in local Fe concentration in the ionomer phase) is expected to favour the reprecipitation of leached Fe cations as Fe oxide. [61] The question now arises whether the release of Fe cations in the electrolyte was caused or simply accelerated by the corrosion of the carbon matrix.…”

Section: Fe Redistribution At the Electrode  Electrolyte Interfacementioning

confidence: 77%

Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Sgarbi

Kumar

Saveleva

et al. 2022

Applied Catalysis B: Environmental

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Section: Fe Redistribution At the Electrode  Electrolyte Interfacementioning

confidence: 77%

Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Sgarbi

Kumar

Saveleva

et al. 2022

Applied Catalysis B: Environmental

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“…The results at different times of operation show a reduction in the local IEC values in the cathode CL and in the membrane close to the cathode catalyst layer. This reduction indicates a degradation of the ionomeric materials, which is based on lower hydration levels at the cathode and causes performance decay over time, as previously discussed. ,,,, Thus, cathode ionomer and membrane degradation might be the reason for the observed degradation products in IC analysis. Back diffusion of water from the anode to cathode might compensate for low hydration levels at the cathode, but even for high water diffusivity values, lower hydration levels were observed at the cathode. ,,, Change in the anode catalyst to a PtRu material as carried out in recent AEMFC studies might improve the water level at the cathode due to the enhanced kinetics of the hydrogen oxidation reaction and thus produce more water that can diffuse to the cathode. , Also, the volumes of sampled exhaust water differ between the anode and the cathode side (Tables S3–S6).…”

Section: Resultsmentioning

confidence: 62%

“…Furthermore, the model calculates the chemical degradation kinetics of the ionomeric materials in the anode and cathode CLs and the membrane, whose local kinetics is set by the local water content. The model can predict the performance and performance stability of AEMFCs (time changes in IEC, represented by the hydroxide ion concentration). ,, …”

Section: Methodsmentioning

confidence: 99%

“…The model can predict the performance and performance stability of AEMFCs (time changes in IEC, represented by the hydroxide ion concentration). 23,24,40 The model is validated against the experimental data for AEMFCs operated with RH values of 95/95 at the anode and the cathode by tuning a single parameter for fitting the entire data set, namely, the cathode electrochemical surface area. The remaining model parameters were derived from the experimental measurements.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Impact of the Relative Humidity on the Performance Stability of Anion Exchange Membrane Fuel Cells Studied by Ion Chromatography

Lorenz

Janßen

Yassin

et al. 2022

ACS Appl. Polym. Mater.

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Although substantial improvement of the performance of anion exchange membrane fuel cells (AEMFCs) was achieved, longevity is still the main challenge for the AEMFC technology, which is attributed to the degradation of the functional groups of applied membranes and ionomers. Contrary to ex situ material stability studies, we demonstrate here the application of ion chromatography to quantify the amounts of degradation products in the exhaust water during different fuel cell operation conditions on the example of trimethylbenzyl ammonium as a functional group. Higher amounts of degradation products were detected directly after equilibration and completion of polarization curves compared to performance stability measurements under constant load. Moreover, the performance stability dependent on the relative humidity of the anode and cathode feed gases was evaluated. Elevated losses of ionic groups were observed in the anode exhaust water at high humidity fuel cell operation, although higher degradation rates were determined for the cathode side by modeling the performance stability. In contrast, higher amounts of degradation products were detected in the cathode exhaust water under low humidity conditions. However, the mobility of water and degradation products under different fuel cell operation conditions impedes a detailed allocation of the observed degradation to one electrode. The demonstrated combination of in situ electrochemical measurements, corresponding ex situ degradation measurements, and modeling data gives comprehensive insights into the evaluation of the performance stability of anion exchange membrane materials under fuel cell operation, which could exceed ex situ durability experiments based on the membrane materials itself.

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“…Though anion exchange membrane fuel cells (AEMFCs) have historically suffered from low performance and durability, − they have seen a surge in performance over the past few years, with several research groups advancing their achievable peak power density, current density, and longevity. − State-of-the-art AEMFCs are now able to achieve peak power densities of 3.5 W cm –2 operating on H 2 /O 2 and 1.75 W cm –2 operating on H 2 /air (CO 2 -free). ,,, These advances have been possible because of new reactor engineering that carefully manages the quantity and distribution of cell water − as well as the emergence of high-performance anion exchange membranes (AEMs), − anion exchange ionomers (AEIs), , and efficient electrocatalysts. − …”

Section: Introductionmentioning

confidence: 99%

Understanding Recoverable vs Unrecoverable Voltage Losses and Long-Term Degradation Mechanisms in Anion Exchange Membrane Fuel Cells

et al. 2022

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Anion exchange membrane fuel cells (AEMFCs) have recently shown excellent progress in terms of their performance – e.g., achievable power and current density. However, very few AEMFCs have been demonstrated with the ability to operate for a long duration (>1000 h). In addition, it is unknown whether performance losses observed during operation are reversible, irreversible, or a combination of the two. In this study, a high-performance AEMFC operated continuously at 600 mA/cm2 for 3600 h (150 days) at 80 °C with H2/O2 reacting gases was demonstrated. Throughout testing, the electrochemical properties of the AEMFC were probed to provide information about performance degradation pathways and their degree of reversibility. It was found that a portion of the performance loss that occurs during AEMFC operation was due to suboptimal reaction conditions and can be recovered. At the end of the experiment, the cell was disassembled, and its structure and composition were evaluated at the nanoscale by aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. The structure and composition of the electrode were compared to cells at the beginning of their operational life. It was found that the primary mechanism for long-term AEMFC performance loss was catalyst agglomeration. During the operational time, there was no evidence of significant polymer degradation, likely due to the high hydration state of the cell. By documenting the long-term changes in high-performing AEMFCs, this work provides important information for the systematic design of cell components and demonstrates the importance of controlling cell operation, which can aid in the commercialization and widespread deployment of low-cost, long-life AEMFCs.

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Understanding how single-atom site density drives the performance and durability of PGM-free Fe–N–C cathodes in anion exchange membrane fuel cells

Cited by 29 publications

References 76 publications

Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Impact of the Relative Humidity on the Performance Stability of Anion Exchange Membrane Fuel Cells Studied by Ion Chromatography

Understanding Recoverable vs Unrecoverable Voltage Losses and Long-Term Degradation Mechanisms in Anion Exchange Membrane Fuel Cells

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