Controllable Lattice Expansion of Monodisperse Face-Centered Cubic Pd–Ag Nanoparticles for C₁ and C₂ Alcohol Oxidation: The Role of Core–Sheath Lattice Mismatch

Abstract

Direct alcohol fuel cells are considered as promising and sustainable power sources to address global climate change as well as energy and environmental problems. However, designing efficient catalysts for the oxidation of alcohol molecules remains challenging. This study reports the synthesis of monodisperse PdAg nanoparticles (NPs) with face-centered cubic structures with controllable alloying degrees and particle diameters for improving oxidation of ethanol and methanol. Interestingly, the lattice enlargement of the silver-rich core leads to the lattice expansion of the palladium-rich sheath. The lattice expansion of the interface of the NPs leads to the upshifting of the d-band center of Pd toward the Fermi level followed by the stronger binding of a small molecule. The PdAg NPs exhibit "volcano-type" behavior, where the maximum electrocatalytic activity is governed by the balance of the adsorption energies of OH* (reactive intermediates) and CO* (blocking species). The Pd 5 Ag 1 NPs exhibit electrocatalytic activities of 2402 and 1541 mA mg Pd −1 for ethanol oxidation reaction and methanol oxidation reaction in alkaline solution, respectively, about four and three times those of the commercial Pd/C catalysts. The enhanced mass activities of the catalysts can be further analyzed by density functional theory calculations, indicating that the lattice expansion after including silver would lead to the upshifting of the d-band center followed by the strengthened OH* binding. This work discloses a promising way to build novel nanocatalysts with controllable alloying degrees as efficient fuel cell catalysts.

Bimetallic Face-Centered Cubic Pd–Ag Nano-dendritic Alloys Catalysts Boost Ethanol Electrooxidation

“…As shown in the TEM images (Figure 1e−l), the nanoparticle diameters of the four alloy samples were around 12.5 ± 3.1, 12.2 ± 3.0, 13.4 ± 3. 7,32 The elemental distributions in Pd 5 Ag 1 NDA revealed by the HAADF-STEM (Figure 2) show that Pd and Ag elements were distributed evenly and there was successful formation of a homogeneous alloy. 15,32 The XRD patterns of PdAg NDAs are shown in Figure 3a.…”

“…7,32 The elemental distributions in Pd 5 Ag 1 NDA revealed by the HAADF-STEM (Figure 2) show that Pd and Ag elements were distributed evenly and there was successful formation of a homogeneous alloy. 15,32 The XRD patterns of PdAg NDAs are shown in Figure 3a. For Pd 5 Ag 1 NDA, four diffraction peaks are observed at around 39.5, 45.9, 67.1, and 79.9°corresponding to the (111), ( 200), (220), and (311) crystal planes of the fcc structure pure Pd [JCPDS no.…”

“…Lattice shrinkage or expansion can be verified by the positive or negative shift of the diffraction peaks, respectively. 1,15,32 It is worth noting that ML has great potential to accelerate the development of homogeneous and heterogeneous catalysis in the near future. 3 Herein, we report a class of bimetallic Pd−Ag nano-dendritic alloy (NDA) electrocatalysts with tunable tensile strain using a hydrothermal method.…”

Unveiling the Synergistic Effects of Monodisperse Sea Urchin-like PdPb Alloy Nanodendrites as Stable Electrocatalysts for Ethylene Glycol and Glycerol Oxidation Reactions

“…There is a strong electronic interaction between Pb and Pd elements because of the transfer of intra-atomic charge. In addition, as the radius of Pb is larger than that of Pd, the peaks upshifted from Pd 6 Pb to Pd 3 Pb because the lattice expansion shifted the bands closer to the Fermi level (Table S2), and this would lead to the enhancement of the absorptions of the small molecules …”

“…Nowadays, developing clean and sustainable energy in our society has become increasingly more urgent to address global climate change as well as the energy and environmental problems. − For fuel cells, hydrogen (H 2 ) and many alcohols (like methanol and ethanol) are widely utilized at home and abroad. Direct alcohol fuel cells (DAFCs) have attracted great research attention due to their green, sustainable, and environmentally friendly characteristics with large energy densities instead of traditional fossil fuels. − Ethylene glycol and glycerol possess large energy densities and have the advantages of safe storage and low toxicity. , Pt-based materials are widely applied as metal catalysts in fuel oxidation reactions. , The poor performance of the Pt-based materials in an alkaline medium further suppresses their utilization on a large scale. As a result, Pd catalysts have become popular among various metals owing to their abundance in Earth’s crust and low cost.…”