Bimetallic Aerogels: High‐Performance Electrocatalysts for the Oxygen Reduction Reaction

Liu, Wei; Rodríguez, Paramaconi; Borchardt, Lars; Foelske, Annette; Yuan, Jinghe; Herrmann, Anne‐Kristin; Geiger, Dorin; Zheng, Zhikun; Kaskel, Stefan; Gaponik, Nikolai; Kötz, R.; Schmidt, Thomas J.; Eychmüller, Alexander

doi:10.1002/anie.201303109

Cited by 255 publications

(295 citation statements)

References 40 publications

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“…In addition, recent work on Pt-Pd aerogel catalysts has shown that the Pt surface enrichment induced by dealloying leads to enhancement of both the activity and the stability. 47 The result for the nanosized catalysts correspond to that for the present extended surfaces.…”

Section: Resultssupporting

confidence: 74%

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Bando

Takahashi

Todoroki

et al. 2015

J. Electrochem. Soc.

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Electrocatalytic properties for oxygen reduction reaction (ORR) of Pt(111) epitaxial layers on a Pd(111) substrate are investigated. Scanning tunneling microscopy images of the as-prepared 0.6-nm-and 1.2-nm-thick Pt(111) epitaxial layers on Pd(111) (Pt 0.6nm /Pd(111) and Pt 1.2nm /Pd(111)) revealed that the topmost surface has atomically flat, 50-100-nm-wide terraces. Remarkable current features due to hydrogen storage and emission by the Pd(111) substrate dominated the cyclic voltammograms of Pt 0.6nm /Pd(111) in the potential range of 0.15-0.4 V vs. a reversible hydrogen electrode. In contrast, the curve of Pt 1.2nm /Pd(111) exhibited a shrinkage in the hydrogen charges (Q H ) in the potential range of 0.25-0.4 V, accompanied by the emergence of symmetrical redox features at 15 mV on the positive potential side, relative to Pt(111) "butterfly" feature. Both Pt 0.6nm /Pd(111) and Pt 1.2nm /Pd(111) showed ca. four times higher ORR activity than clean Pt(111), although their hydrogen-related behaviors and activity changes during applying potential cycles were much different. The results suggest that shrinkage in Q H and positive shift in the onset potential of hydroxyl species are common features of the CV of highly ORR-active well-defined Pt-M(111) bimetallic surfaces and that the activity enhancements and the structural stabilities fairly depend on the surface structure of the epitaxial Pt (111) High-performance low-cost polymer electrolyte membrane fuel cells (PEMFC) are required for wide-spread use in fuel cell vehicles. Developments in highly active oxygen reduction reaction (ORR) catalysts are one of the top priorities for developing PEMFC stacks. Since the pioneering work on Pt-M (M is a more affordable, lowcost material) alloys by Watanabe and co-workers, 1 numerous studies on the ORR properties of Pt-M bimetallic alloy with nanosized structures have been intensively performed. To date, several types of nanosized structures of Pt-M have been proposed for use as highperformance ORR catalysts, e.g., Pt-shell and M-core core-shell nanoparticles (NPs), 2-5 especially electrochemically de-alloyed M from Pt-M NPs, 6-9 nanostructured thin films of Pt-M, 10,11 shapecontrolled Pt-M NPs, [12][13][14][15] and nanoframe structures of Pt-Ni alloy. 16Irrespective of the proposed nature of the nanosized structures, the generation of electrochemically stable Pt-shell layers at the topmost surfaces is the consensus for synthesizing Pt-M ORR catalysts with high activity and durability. 17-20The topmost atomic-level structures of the Pt-shell layers for the Pt-M bimetallic alloys determine ORR performance. However, because ORR is governed by many factors, the discussions of ORR enhancement mechanisms are intricate. For example, atomic arrangements of the topmost Pt-shell, thickness of the Pt-shell layers, and interface structures between the surface Pt-shell and underlying M (Pt-M) core [21][22][23][24] are expected to have a serious influence on the ORR activities. When studying the topmost surface structures and the eval...

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Section: Resultssupporting

confidence: 74%

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Bando

Takahashi

Todoroki

et al. 2015

J. Electrochem. Soc.

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“…A way to overcome these problems could be hydro-or aerogelation of metals and metal oxides [14][15][16][17][18]. It is reported that high voluminous structures out of NCs, which also partly possess the properties of their respective colloidal solution, can be achieved [16,19,20]. Nonetheless aerogelation itself is a complicated multi-step process.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Properties of Cryogelated Noble Metal Aerogels

Freytag

Colombo

Bigall

2016

Zeitschrift Für Physikalische Chemie

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Abstract:The catalytic properties of cryogelated noble metal aerogel monoliths out of aqueous colloids are investigated using the oxidation of carbon monoxide (CO) as a model reaction, in order to evaluate their potential for catalytic applications. Aerogels built of self-supporting platinum (Pt) and palladium (Pd) nanocrystals (NCs) have a directly accessible catalyst surface and show catalytic performance similar to state of the art catalysts while being support-free and therefore ultralight materials. In addition, these materials provide properties like room temperature CO conversion and spontaneous catalytic reactions. However, full material aerogel catalysts come with the side effect of limited thermal stability, which will have to be overcome in future.

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“…On the basis of previous work on Pt-Pd alloy aerogels prepared with the aforementioned method, 20 we have adapted our synthetic approach to the combination of a noble and a non-noble metal, targeting a reduced noble metal content while maintaining a high ORR activity. As we will demonstrate in this article, the combination of Pt and Ni yielded materials with a mass-normalized ORR activity ≈2-fold = These authors contributed equally to this work.…”

mentioning

confidence: 99%

“…In contrast to those approaches, our groups have developed a facile one-step synthesis for mono-and bimetallic aerogels based on the reduction of metal salts by NaBH 4 in aqueous solution without addition of stabilizing surfactants. 20 On the basis of previous work on Pt-Pd alloy aerogels prepared with the aforementioned method, 20 we have adapted our synthetic approach to the combination of a noble and a non-noble metal, targeting a reduced noble metal content while maintaining a high ORR activity. As we will demonstrate in this article, the combination of Pt and Ni yielded materials with a mass-normalized ORR activity ≈2-fold = These authors contributed equally to this work.…”

mentioning

confidence: 99%

Pt-Ni Aerogels as Unsupported Electrocatalysts for the Oxygen Reduction Reaction

Henning

Kühn

Herranz

et al. 2016

J. Electrochem. Soc.

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The commercial feasibility of polymer electrolyte fuel cells (PEFCs) passes by the development of Pt-based, O 2 -reduction catalysts with greater activities and/or lower Pt-contents, as well as an improved stability. In an effort to tackle these requirements, unsupported bimetallic Pt-Ni nanoparticles (NPs) interconnected in the shape of nanochain networks (aerogels) were synthesized using a simple one-step reduction and gel formation process in aqueous solution. The products of this novel synthetic route were characterized by X-ray absorption spectroscopy to elucidate the materials' structure. Using electrochemical experiments, we probed the surface composition of the as-synthesized aerogels and of equivalent materials exposed to acid, and concluded that a Ni-(hydr)oxide side phase is present in the aerogel with a larger Ni-concentration. Regardless of this initial surface composition, the Pt-Ni aerogels feature a ≈3-fold increase of surface-specific ORR activity when compared to a commercial platinum-on-carbon catalyst, reaching the mass-specific requirement for application in automotive PEFCs. 1 to account for the large overpotential of the oxygen reduction reaction (ORR). Thus, Pt contributes significantly to the fuel cell system cost, and progress to reduce its loading is crucial to meet the long-term PEFC cost target of 40 $/kW set by the U. S. Department of Energy (DOE).2 One approach to reduce this excessive Pt-loading relies on increasing the catalysts' ORR activity, e.g. by alloying platinum with other metals like Ni, Cu and Co, to form materials which show up to one order of magnitude higher mass-specific activity than commercial Pt/C catalysts.3 On the other hand, these carbon-supported materials suffer from significant carbonand Pt-corrosion during the standard operation of PEFCs, gradually compromising their efficiency and reliability. 4 To partially overcome stability issues, research focuses on unsupported materials (e.g. Ptcoated Ni, Co or Cu nanowires 5-7 ) besides extended metal surfaces (e.g. 3 M nanostructured thin film catalysts 8 ) or alternative supports (e.g. conductive metal oxides 9-12 ). Naturally, those materials should be processable into catalytic layer architectures that provide reactant and product diffusion pathways similar to those in conventional Pt/C electrodes to guarantee high catalyst utilization and PEFC performance. 13To meet the requirements mentioned above, un-supported bimetallic electrocatalysts with high surface area (up to ≈80 m 2 /g metal ) and nanochain network structure, referred to as aerogels, have been synthesized. [14][15][16] The synthetic routes to prepare such materials vary, but generally involve the use of stabilizing surfactants and/or organic solvents [17][18][19] that can poison the catalyst's surface and decrease its activity. In contrast to those approaches, our groups have developed a facile one-step synthesis for mono-and bimetallic aerogels based on the reduction of metal salts by NaBH 4 in aqueous solution without addition of stabilizing surfac...

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Bimetallic Aerogels: High‐Performance Electrocatalysts for the Oxygen Reduction Reaction

Cited by 255 publications

References 40 publications

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Electrochemical Properties of Pt Epitaxial Layers Formed on Pd(111) in Ultra-High Vacuum

Catalytic Properties of Cryogelated Noble Metal Aerogels

Pt-Ni Aerogels as Unsupported Electrocatalysts for the Oxygen Reduction Reaction

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