Ordered bilayer ruthenium–platinum core-shell nanoparticles as carbon monoxide-tolerant fuel cell catalysts

Abstract

Fabricating subnanometre-thick core-shell nanocatalysts is effective for obtaining high surface area of an active metal with tunable properties. The key to fully realize the potential of this approach is a reliable synthesis method to produce atomically ordered core-shell nanoparticles. Here we report new insights on eliminating lattice defects in core-shell syntheses and opportunities opened for achieving superior catalytic performance. Ordered structural transition from ruthenium hcp to platinum fcc stacking sequence at the core-shell interface is achieved via a green synthesis method, and is verified by X-ray diffraction and electron microscopic techniques coupled with density functional theory calculations. The single crystalline Ru cores with well-defined Pt bilayer shells resolve the dilemma in using a dissolution-prone metal, such as ruthenium, for alleviating the deactivating effect of carbon monoxide, opening the door for commercialization of low-temperature fuel cells that can use inexpensive reformates (H 2 with CO impurity) as the fuel. O ne major goal in electrocatalysis studies is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). This is the key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells 1,2 . An effective approach is to fabricate core-shell nanoparticles (NPs) that have active, corrosion-resistant Pt atoms on the surface, with tunable reactivity through their interactions with other metal cores to assure optimal catalytic performances. At the cathode, Pt monolayer (ML) catalysts with Pd or Pd 9 Au alloy cores exhibited enhanced activity and durability for the oxygen reduction reaction compared with Pt NPs 3 . Furthermore, both experimental and theoretical studies verified that lattice contraction 4-7 , high-coordination (111) facets 8-10 and smooth surface morphology 11 are beneficial structural factors in enhancing oxygen reduction reaction activity and the catalysts' durability.For the hydrogen oxidation reaction (HOR) at the anode, a negligible overpotential loss was achieved with pure hydrogen using 50 mg cm À 2 Pt NPs 12,13 . However, the challenge remains in employing inexpensive reformate hydrogen, wherein the p.p.m.-level of carbon monoxide (CO) impurities can severely deactivate the Pt catalysts [14][15][16] . In addition, although the anode operates at relatively low potentials, its nanocatalysts must be dissolution resistant because of the high potentials experienced during startups and shutdowns 17,18 . For developing CO-tolerant HOR catalysts, ruthenium (Ru) was used to support spontaneously deposited sub-ML Pt 19,20 . With about a one-to two-ML-thick Ru(core)-Pt(shell) (denoted as Ru@Pt) NPs, theoretical calculations and temperatureprogrammed measurements showed preferential CO oxidation in hydrogen feeds on Ru@Pt NPs compared with that of Ru-Pt nano-alloys 21 and of Pt shells with other metal core 22 . Besides being a promoter of CO tolerance of Pt surface, Ru ...

CO electro-oxidation reaction on Pt nanoparticles: Understanding peak multiplicity through thiol derivative molecule adsorption

“…CO electro-oxidation is important for both proton-exchange membrane fuel cells [1][2][3] and direct methanol fuel cells [4,5]. Due to its importance, CO electro-oxidation has been extensively studied for many years.…”

Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

“…7 Recently, it was found that the catalyst and the proper non-aqueous electrolyte are the key factors to address these problems. 8 Therefore, various electrocatalysts, including carbons, metal oxides, metal nitrides and precious metals have been examined as the cathode catalysts in Li-O 2 cells to lower the charge overpotential. 9 It was reported that the use of catalysts can decrease the charge potential tõ 3.8 from~4.2 V. 10 It has been shown, however, that the theoretical overcharge potential for a Li 2 O 2 film is only 0.2 V, if there are no limitations on charge transport through Li 2 O 2 to the Li 2 O 2 -electrolyte interface.…”

Plasmonic gas and chemical sensing

“…Furthermore, the combination of multiple materials in complex core-shell nanoparticles and the use of advanced synthesis procedures allow for new functionalities as well as increased flexibility in structure design [47][48][49]. Implementing this concept for plasmonic gas sensing, Ghodselahi et al have demonstrated the use of Cu@CuO core-shell nanoparticles for the detection of carbon monoxide [50].…”