Anode Electrocatalysts for Direct Borohydride and Direct Ammonia Borane Fuel Cells

Olu, Pierre-Yves; Zadick, Anicet; Job, Nathalie; Chatenet, Marian

doi:10.1002/9783527803873.ch10

Cited by 5 publications

(9 citation statements)

References 93 publications

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“…The higher activity of the Fe@N-C active sites in alkaline medium can be assigned to the enhancement of electrical conductivity of nitrogen-carbon and a synergistic effect between the metallic centers and the nitrogen-carbon shell. This is in line with recent results demonstrating that a higher degree of graphitization of carbon is beneficial to the electrical conductivity [42] and that synergies between the nitrogen-carbon shell and metallic centers contribute to efficient ORR electrocatalysis [19,28,[43][44][45][46] Another aspect to be discussed is the cause of the positive shift on the onset potential when the pH is changed from low to high values. This fact may be related to the OHads coverage and its desorption to regenerate the active metallic center M 2+ [5,18,21].…”

Section: Resultssupporting

confidence: 83%

“…Along the same lines, the high ORR activity of Fe-N-C catalysts has been clearly linked to the content of Fe-NxCy sites, especially in low pH conditions [7,27]. However, it has been recently reported that Fe-N-C catalysts containing Fe@N-C core-shell structures (without Fe-NxCy moieties) also can exhibit good ORR activity, either in high or in low pH conditions [19,28,29]. In summary, it is well-established that optimized M-N-C catalysts can achieve high activities towards ORR electrocatalysis, sometimes approaching those of PGM-based materials.…”

Section: Introductionmentioning

confidence: 99%

“…Many studies have investigated the nature of the different ORR active sites in M-N-C catalysts [18][19][20], and three main types of active sites have been proposed: NxCy, M-NxCy, and M@N-C [7], where NxCy sites are nitrogen functional groups in a carbon matrix, M Regarding Co-N-C catalysts, Co-NxCy moieties have been pointed as the main active centers that catalyze the ORR, either in alkaline or acidic conditions [24][25][26]. Meanwhile, Co@N-C sites have shown ORR activity, with the N-C matrix providing protection of the metallic core, that would otherwise be rapidly leached out in acidic medium [26].…”

Section: Introductionmentioning

confidence: 99%

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Eletrocatalisadores metal-N-C: aspectos físicos e químicos na atividade e durabilidade frente à reação de redução do oxigênio

Moraes¹

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Metal-N-C electrocatalysts (where the Metal is Fe or Co) have been investigated for mitigating the dependence on platinum-group-metals (PGM), when catalyzing the oxygen reduction reaction (ORR) in acidic or alkaline for fuel cell technologies. This thesis relates the activity, durability and poisoning resistance with the physicochemical properties of such electrocatalysts with iron and cobalt. The investigated materials contain two main active groups: (i) atomicallydispersed metals attached to nitrogen-doped carbon networks (M-NxCy active sites) and (ii) metal nanoparticles encased on nitrogen-doped carbon shells (M@N-C active sites). Regarding the activity, Fe-N-C is more active than the Co-based catalysts, either at low and high pHs. Fe-NxCy sites present the highest ORR activity in acid media, amplified by an adequate energy binding between the metallic center and oxygenated reaction intermediates. In contrast, Fe@N-C core-shell sites present maximum ORR mass activity in alkaline media, promoted by a synergistic effect involving catalyst particles with metallic iron in the core and nitrogen-doped carbon in the shell. The durabilities tests have shown two main degrading processes that may occur on the catalyst: (i) oxygenated and nitrogen functional groups interconversion and/or oxidation and (ii) demetallation of the metallic center. Iron nanoparticulated catalyst centers undergo more severe carbon degradation and nitrogen/oxygenated functional groups interconversion (and/or oxidation) than the atomically dispersed iron centers. But, this latter catalyst losses metal severely, which is re-deposited growing in situ Fe-based nanoparticles after accelerated stressing tests under O2 atmosphere, more at 25 °C than at 60 °C. As a consequence, the atomically dispersed iron-based nanoparticles drop the ORR mass activities less intensely. Further, the atomically dispersed Fe-and Co-containing electrocatalysts have better BH4 −-tolerance than bare Fe and Co nanoparticles. The atomically dispersed iron electrocatalysts, the material with the highest micropores area, present slight advantage of ORR mass activity in the presence of BH4anions. Finally, these features place the atomicallydispersed iron as a promising candidate for the investigations in direct borohydride fuel cell (DBFC) and as an excellent candidate for application in the cathode of anion-exchange membrane fuel cell (AEMFC).

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Section: Resultssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Eletrocatalisadores metal-N-C: aspectos físicos e químicos na atividade e durabilidade frente à reação de redução do oxigênio

Moraes¹

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“…The Proton Exchange Membrane Fuel Cell (PEMFC) is a very promising solution for electricity generation in transportation and stationary applications [1][2][3]. Its principle relies on the oxidation of hydrogen (at the anode) and the reduction of oxygen (at the cathode), while a proton-conducting membrane (Nafion Ⓡ , usually) allows for the charge transport in-between.…”

Section: Introductionmentioning

confidence: 99%

A practical method to characterize proton exchange membrane fuel cell catalyst layer topography: Application to two coating techniques and two carbon supports

et al. 2020

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The coating technique and the type of carbon support can strongly affect the surface topography, the homogeneity and the thickness of the catalyst layers of Proton Exchange Membrane fuel cells. These features can in turn strongly modify the local diffusion properties of the layer and the final cell performance, but literature about catalytic layers does not often address such issues. This work aims at studying the topography of proton exchange membrane fuel cell catalyst layers by means of 3D characterization methods. For that purpose, two types of slurries, made of Nafion Ⓡ and carbon black or a carbon xerogel, have been coated on a Kapton Ⓡ sheet by film-casting and by spray-coating. The surface topography of the samples was characterized by contact profilometry and 3D laser scanning microscopy. The data obtained with both methods were processed in order to obtain accurate 3D representations of the surface of the layers. Contact profilometry allows to perform measurements over the entire surface of the sample (5 cm × 5 cm). Layers obtained by film-casting turn out to be very smooth, but also thinner at the edges of the coating. For layers prepared by spray-coating, the reproducibility and the homogeneity are improved; however, the surface displays a higher roughness. With 3D laser scanning microscopy measurements, only a small part of the sample was analyzed (0.25 cm 2) with a high definition, allowing to characterize more precisely the surface topography. The comparison of both techniques has been enriched by the simulation of the profilometer tip motion at the surface of the observed 3D microscopy profile, giving insight into the observed differences. The 3D microscopy measurements proved to be more accurate, but not representative of the whole sample, especially for less homogeneous layers prepared by filmcasting.

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“…Of course, the direct oxidation of the borohydride anion (BH4 -) in a direct borohydride fuel cell (DBFC) is not an easy process, and many works addressed the issue, so as to isolate the reaction mechanisms [12][13][14][15][16][17][18], the proper electrocatalysts for the anode [19] and the ideal fuel composition, electrode structure, operating parameters of the anode, etc. [20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Oxygen Reduction Reaction on Metal and Nitrogen–Doped Carbon Electrocatalysts in the Presence of Sodium Borohydride

et al. 2020

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Metal and nitrogen-doped carbons electrocatalysts (M-N-C, where M is Fe or Co) are investigated for the oxygen reduction reaction (ORR) in alkaline conditions in the presence of borohydride ions (BH4-). The electrochemical properties of the Fe-N-C and CoN -C catalysts were investigated by cyclic voltammetry and rotating disk electrode 2 techniques: their ORR electrocatalytic activity was bridged to their physico-chemical properties, mainly type of metallic center (Fe vs. Co), structure (atomic dispersion vs. nanoparticles) and BET surface area. It is found that Fe-N-C catalysts have the best performances for the ORR electrocatalysis, even in presence of BH4anions. The atomically-dispersed Fe-and Co-containing electrocatalysts reach better BH4-tolerance than their counterparts baring nanoparticles. For the atomically dispersed Fe-N-C electrocatalysts, the lowest BET surface area material generates a slight advantage of ORR mass activity and a poor (and desired) activity for borohydride oxidation reaction (BOR).

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Anode Electrocatalysts for Direct Borohydride and Direct Ammonia Borane Fuel Cells

Cited by 5 publications

References 93 publications

Eletrocatalisadores metal-N-C: aspectos físicos e químicos na atividade e durabilidade frente à reação de redução do oxigênio

Eletrocatalisadores metal-N-C: aspectos físicos e químicos na atividade e durabilidade frente à reação de redução do oxigênio

A practical method to characterize proton exchange membrane fuel cell catalyst layer topography: Application to two coating techniques and two carbon supports

Oxygen Reduction Reaction on Metal and Nitrogen–Doped Carbon Electrocatalysts in the Presence of Sodium Borohydride

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