Effect of reduction enhancer on a radiolytic synthesis of carbon-supported Pt–Cu nanoparticles and their structural and electrochemical properties

Abstract

In order to clarify the effect of reduction enhancer on the nanoparticle formation process and their structural and catalytic properties, carbon-supported Pt-Cu nanoparticles were synthesized by electron beam irradiation on an aqueous precursor solution in the presence/absence of reduction enhancer. In the absence of reduction enhancer, tetravalent platinum oxide particles of approximately 1 nm in diameter were formed on carbon support with copper barely precipitated, while in the presence of 2-propanol or ethylene glycol or glucose both platinum and copper precipitated as few-nanometer-sized alloy particles together with copper oxides. It was suggested that the metal nuclei produced upon electron beam irradiation do not have enough lifetime without reduction enhancer due to fast oxidation of the nuclei by oxidizing radicals, while the reduction enhancer scavenges these oxidizing radicals preventing oxidation of metallic clusters and prolonging their lifetime. Ethylene glycol gave smaller and better alloyed particles with less copper oxides compared to 2-propanol since the carbonyl compounds derived from oxidation of ethylene glycol protect metallic clusters from oxidation further prolonging their lifetime. In the electrochemical measurements, the methanol oxidation activities of Pt-Cu/C catalysts were well explained by their structural characteristics.

Effect of organic stabilizers on Pt–Cu nanoparticle structure in liquid-phase syntheses: control of crystal growth and copper reoxidation

“…This indicates that the organic stabilizer makes the lifetime of nuclei long enough for all of the copper to be reduced and retained as metallic copper incorporated in Pt lattice and in part reoxidized to copper oxides in the vicinity of platinum. The presence of copper oxide phases was confirmed by the previous X-ray absorption study where the Cu K-edge XANES of Pt-Cu/C was not of metallic Cu alone and the fitting of Cu K-edge EXAFS to a scattering model showed the presence of Cu-O bonds (Kugai et al 2015). Without stabilizer, the lifetime of nuclei is too short for copper to meet platinum leaving some ionic copper unreduced in the suspension together with large platinum-rich particles.…”

“…For the case that a stabilizer molecule has hydroxyl groups, it also functions as a reductant (for scavenging OH radicals formed by water radiolysis). For instance, glycolate, generated during an electron beam irradiation on a precursor suspension containing EG, functioned as a stabilizer and a reductant at the same time during the radiolytic method (Kugai et al 2015). However, the influence of molecular structure of stabilizers on nanoparticle formation process is complicated and, to our knowledge, only few papers focus on the molecular structure of stabilizers as a factor to control the nanoparticle structure.…”

Facile Synthesis of Pt-Cu (Ni, Co)/GNs-CD and Their Enhanced Electro-Catalytic Activity for Methanol Oxidation

“…42 in the Pt catalyst reducing, resulting in the decrease of oxidation current for Pt-Cu/GNs-CD catalysts. 44,45 It is reported that the excessive amount of non-noble metal may bring about less Pt-rich surface and not be in favor of catalyzing methanol oxidation reaction because that the electro-oxidation of methanol involves multistep adsorption and electron transfer and requires various adjacent Pt active sites. 45 For the same reason, it is found that current density of Pt 1 -Ni 0.7 /GNs-CD (curve b) and Pt 1 -Co 0.4 /GNs-CD (curve b) are the highest among other composites with different metal molar ratio in Fig.…”

Nanoparticle Alloy Formation by Radiolysis

“…A chelate agent, tartaric acid, has been added to enhance the alloying potential of Pt and Ru supported on a carbon support during irradiation with an electron beam of 4.8 MeV at room temperature (3 kGy/s) . More recently, the same group proposed the use of ethylene glycol as an organic stabilizer to promote Pt–Cu alloy formation using the same electron beam irradiation process . The authors claimed that the ethylene glycol protects the Cu metallic clusters and prevents them from the competing oxidation reaction.…”

“…73 More recently, the same group proposed the use of ethylene glycol as an organic stabilizer to promote Pt−Cu alloy formation using the same electron beam irradiation process. 74 The authors claimed that the ethylene glycol protects the Cu metallic clusters and prevents them from the competing oxidation reaction. The effect of carboxylate containing compounds on platinum growth has also been studied.…”