Small palladium islands embedded in palladium–tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction
Our most recent article has been published in the journal of Nature Communications, and here, we report a unique novel Pd-W alloy with a Pd content of only 11 At%, which has a similar efficiency as a pure platinum catalyst. This excellent efficiency is explained by the unique morphology of the Pd-W nanoparticles. By advanced experimental and theoretical investigations, we show that the alloy is composed of metallic Pd-islands embedded in a W matrix. The size of the islands are about 1 nm in diameter and are composed of 10-20 atoms that are segregated to the surface. The unique formation of the material is based on the synthesis method, which is performed in an ordinary kitchen micro-wave oven. This study has been conducted in "The artificial leaf" project which is funded by Knut and Alice Wallenberg foundation to physicist, chemists, and plant science researchers at Umeå University.
Guangzhi Hu, Florian Nitze, Eduardo Gracia-Espino, Jingyuan Ma, Hamid Reza Barzegar, Tiva Sharifi, Xueen Jia, Andrey Shchukarev, Lu Lu, Chuansheng Ma, Guang Yang, and Thomas Wågberg
Nature Communications 5, Article number:5253 (2014)
The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world.
Here we demonstrate an efficient synthesis of palladium–tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium:tungsten=1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium–tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are ~1 nm in diameter, and contain 10–20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.
Palladium Nanocrystals Supported on Photo-transformed C60 Nanorods: Effect of Crystal Morphology and Electron Mobility on the Electrocatalytic Activity Towards Ethanol Oxidation.
This article has been recently published in the journal Carbon, and here, we report the synthesis C60 nanorods (NRs) and its subsequent decoration with palladium nanoparticles. We modified the NR surface via in situ photochemical transformation in the liquid state, in order to obtain highly stable NRs that retain their crystalline structure during the decoration process. We also show that the photo-transformed C60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity.
Hamid Reza Barzegar, Guangzhi Hu, Christian Larsen, Xueen Jia, Ludvig Edman, and Thomas Wågberg
Carbon, Vol 73, Pages 34–40 (2014)
We report on the synthesis and decoration of high-aspect-ratio crystalline C60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 ± 0.66 nm. In their pristine form, C60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process.
TEM image of the synthesized C60 NRs using liquid–liquid interfacial precipitation method.
Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C60 NRs. Bys measuring the electron mobility of different C60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.
Understanding the Interface of Six-Shell Cuboctahedral and Icosahedral Palladium Clusters on Reduced Graphene Oxide: Experimental and Theoretical Study
This is our most recent work published in the Journal of American Chemical Society. Here we studied the nanoscale interactions of reduced graphene oxide (rGOx) homogeneously decorated with small palladium nanoclusters (2.3 ± 0.3 nm). The Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are consistent with six-shell cuboctahedral and icosahedral clusters containing ∼600 Pd atoms. We also performed ab initio simulations to understand the electronic properties of the graphene−nanoparticle hybrid system.
This article has been published as an open access, so here you can download the published version of the article.
Eduardo Gracia-Espino, Guangzhi Hu, Andrey Shchukarev, and Thomas Wågberg.
J. Am. Chem. Soc., 2014, 136 (18), pp 6626–6633
Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 ± 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing ∼600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdOx shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene−nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with functionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.