Utilizing ink composition to tune bulk-electrode gas transport, performance, and operational robustness for a Fe–N–C catalyst in polymer electrolyte fuel cell

Osmieri, Luigi; Wang, Guanxiong; Cetinbas, Firat C.; Khandavalli, Sunilkumar; Park, Jae-Hyung; Medina, Samantha; Mauger, Scott A.; Ulsh, Michael; Pylypenko, Svitlana; Myers, Deborah J.; Neyerlin, Kenneth C.

doi:10.1016/j.nanoen.2020.104943

Cited by 69 publications

(60 citation statements)

References 79 publications

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“…The CL is commonly fabricated through a solution processing method, where a catalyst inka mixture of the catalyst and ionomer in a dispersion medium (DM, typically a water–alcohol mixture)is formulated, coated on a substrate (gas diffusion layer, membrane, or decal), and then dried. The CL structure is well known to significantly affect the performance of fuel cells as it dictates the transport of reactants (H 2 and O 2 ) and products (H + , e – , and H 2 O) to and from the catalyst active sites. , For PGM-free cathode CLs, mass and proton transport plays a critical role in determining the fuel-cell performance because of the much larger thickness (50 μm) than the conventional PGM cathode CL. , Simulations and experiments have shown the performance to be highly sensitive to the porosity, tortuosity, and conductivity of the CL. − Experimental studies have additionally shown that the performance is highly dependent on the amount of the ionomer, as it can affect both proton and mass transport. , Furthermore, our recent research (Osmieri et al) has shown that changes to the water/1-propanol ( n PA) ratio in the DM of PGM-free catalyst inks have a profound effect on the CL structure, as they modify both the porosity and ionomer distribution. These findings highlight the need to better understand how the catalyst ink and the interparticle interactions within the ink are influencing the CL structure for PGM-free catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…From extensive research on PGM CLs, many studies have demonstrated that the ink microstructure is dependent on the particle surface chemistry and formulation parameters such as DM composition − and ionomer concentration. − Catalyst inks are generally found to be agglomerated in the absence of an ionomer . The addition of an ionomer was found to reduce the agglomerated structure (i.e., stabilize the particles against agglomeration) of most catalyst/carbon inks (Pt-Vulcan, iridium oxide, Vulcan, high-surface area carbon), with an exception of Pt on high surface carbon. , Beyond the catalyst and ionomer, the DM type and composition (i.e., water/alcohol ratio) have also been found to affect the structure, performance, and stability of the resulting electrode. − ,, …”

Section: Introductionmentioning

confidence: 99%

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Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe–N–C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

et al. 2020

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We present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe−N−C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1propanol (nPA). The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (H 2 O %) in the DM on the ink microstructure were studied. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks. In the absence of the ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure for catalyst concentrations as low as 2 wt %. The effect of H 2 O % in the DM on particle agglomeration was found to vary with particle concentration. In concentrated inks (≥2 wt % catalyst), increasing H 2 O % was found to increase agglomeration because of the hydrophobic nature of the catalysts. In dilute inks (<1 wt % catalyst), the trend was reversed with increasing H 2 O %, suggesting that electrostatic interactions are dominating the behavior. In inks with 5 wt % catalyst, the addition of an ionomer was found to significantly stabilize the catalyst against agglomeration. Maximum stability was observed at 0.35 I/C for all DM H 2 O % studied. At high ionomer concentrations (I/C > 0.35), interesting differences were observed between nPA-rich inks (H 2 O % ≤ 50%) and H 2 O-rich (82% H 2 O) inks. The nPA-rich inks remained predominantly stableink viscosity only weakly increased with I/C and the Newtonian behavior was maintained for I/C up to 0.9. In contrast, the H 2 O-rich inks exhibited a significant increase in viscoelasticity with increasing I/C, suggesting flocculation of the catalyst by the ionomer. These differences suggest that the nature of the interactions between the ionomer and catalyst is highly dependent on the H 2 O % in the DM.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe–N–C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

et al. 2020

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“…Similar to our previous work with platinum group metal-free electrospun electrodes, a networked structure with micron-sized voids throughout the Pt/Vu NF mat with interfiber porosity between the fiber filaments was observed (Figure b,c). While traditionally fabricated electrodes with packed catalyst aggregates result in lower effective diffusion coefficients, utilizing electrospinning as a method of catalyst integration allows for large continual macropores throughout the bulk electrode structure, which are imperative for HCD PEMFC performance in relatively thicker electrodes.…”

Section: Resultsmentioning

confidence: 99%

“…Microstructure at the ink-level is known to strongly influence the structure of the catalyst layer. 34,44 In our recent studies, we showed how both the ionomer and PAA can interact or adsorb onto the catalyst surface as a function of PAA concentrations. 48 On that note, the differences in the local ionomer coverage on Pt in the fibers fabricated with 10 and 15 wt % PAA seen in this work could also be attributed to the changes in the ionomer/catalyst, PAA/catalyst, and ion/dipolar interactions of the ionomer with the particle surface relative to PAA concentrations at the ink level.…”

Section: H 2 /Air Polarization Curvesmentioning

confidence: 99%

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Microstructure and Pt Accessibility

Kabir

Cleve

Khandavalli

et al. 2021

ACS Appl. Energy Mater.

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This work investigates how local ionomer/platinum (Pt) interactions and ionomer distribution in electrospun Pt/Vulcan nanofiber electrodes impact ionomer coverage, proton accessibility, and oxygen reduction reaction (ORR) performance in proton-exchange membrane fuel cells. Insights from various in situ electrochemical diagnostics were utilized in conjunction with ex situ microscopic characterization to understand how the electrode microstructureboth at the aggregate level and near the ionomer/platinum interfaceis affected by electrospinning in comparison to ultrasonic spraying. The effect of the carrier polymer poly(acrylic acid) (PAA) concentration from 5–20 wt % (with respect to total ink solids) on the resulting nanofiber morphology is discussed. Electron microscopy observations and CO displacement measurements indicated that Pt/Vulcan nanofibers prepared with a higher PAA concentration (15 wt %) were conformally coated with a film of ionomer on the exterior of the fiber, which resulted in an overall lower ionomer coverage on both Pt and carbon throughout the fiber diameter. In contrast, 10 wt % PAA leads to a uniform intrafiber distribution of the ionomer within the fibers, increasing the overall ionomer coverage and proton accessibility under both wet and dry conditions. These differences in the local ionomer coverage on Pt between 10 and 15 wt % PAA were also attributed to differences in the adsorption/interaction affinities between PAA and the ionomer onto the catalyst surface in the ink using zeta potential measurements. Additional fuel cell electrochemical tests on the electrospun electrodes show improvements in ORR kinetics and high-current-density H2/air performance compared to the ultrasonically sprayed electrodes.

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“…13b). Similarly, other parameters such as the ionomer chemical property 78 , ink compositions 85 , drying methods 86 , etc. have also been studied and shown their effects on the cell performance.…”

Section: Effect Of Fabrication Methods Of CCLmentioning

confidence: 99%

Recent Progress in Proton-Exchange Membrane Fuel Cells Based on Metal-Nitrogen-Carbon Catalysts

丁亮¹,

Tang²,

胡劲松³

2020

Acta Physico Chimica Sinica

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Proton-exchange membrane fuel cells (PEMFCs) directly transform chemical energy into electrical energy with high energy density and zero carbon emissions, thereby offering a clean energy alternative for fossil fuels and vehicle electrification. However, the existing PEMFCs rely on Pt-based catalysts, especially at the cathode side wherein the sluggish oxygen reduction reaction (ORR) takes place, resulting in high cost and limiting their commercial applications. Therefore, there is a strong interest in developing platinum group metal-free (PGM-free) PEMFCs. Although impressive advancements have been made since metalnitrogen-carbon (M-N-C) catalysts have been developed as promising candidates for low-cost cathode catalysts, PGM-free PEMFCs still suffer from insufficient activity and durability. Owing to the intricate structure of the tri-phase interface and mass transport limitation, the M-N-C catalysts with high ORR activity in rotating disk electrode (RDE) tests still suffer from unexpected problems such as showing low activity and undesired rapid degradation process in real fuel cell conditions. Therefore, a comprehensive understanding of the active sites and influences of the M-N-C catalyst structure and cathode structure on the PEMFC performance will promote the development of PGM-free PEMFCs. Herein, with an aim to increase the activity and durability of PEMFCs based on M-N-C catalysts, we summarize the recent progress in understanding the active sites of M-N-C catalysts and the relationships between the structures of catalysts/catalyst layers and device performances. At the catalyst level, multiple delicately designed synthetic strategies suggest that attractive device performances can be obtained by tailoring the intrinsic activity and density of the catalyst active sites while engineering the porosity of catalysts to improve the utilization of active sites. Additionally, integrating the catalyst ink into the cathode catalyst layers in PGM-free PEMFC is pivotal for transforming the impressive ORR performance of catalysts in the RDE test to fuel cell performance. Accordingly, the recent advances in the enhancement of mass transfer and charge transport to achieve remarkable fuel cell performance were also included by rationally designing ionomer contents, catalyst morphology, and fabrication process of cathodic catalyst layers. Moreover, durability is the Achilles heel of PEMFCs with M-N-C catalysts, which is currently far behind the commercial requirements. The possible degradation mechanisms and the recent progress in seeking the corresponding solutions are also discussed in this review, including the decomposition of metal species, protonation of nitrogen sites, corrosion of carbon support, and micropore flooding. Based on these insights, the perspective is proposed by articulating open challenges and opportunities in materials innovations and device engineering with an aim to achieve practical M-N-C based PEMFCs.

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Utilizing ink composition to tune bulk-electrode gas transport, performance, and operational robustness for a Fe–N–C catalyst in polymer electrolyte fuel cell

Cited by 69 publications

References 79 publications

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe–N–C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe–N–C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Microstructure and Pt Accessibility

Recent Progress in Proton-Exchange Membrane Fuel Cells Based on Metal-Nitrogen-Carbon Catalysts

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