Microstructural Evolution of Au@Pt Core–Shell Nanoparticles under Electrochemical Polarization

Abstract

Understanding the microstructural evolution of bimetallic Pt nanoparticles under electrochemical polarization is critical to developing durable fuel cell catalysts. In this work, we develop a colloidal synthetic method to generate core–shell Au@Pt nanoparticles of varying surface Pt coverages to understand how as-synthesized bimetallic microstructure influences nanoparticle structural evolution during formic acid oxidation. By comparing the electrochemical and structural properties of our Au@Pt core–shells with bimetallic AuPt alloys at various stages in catalytic cycling, we determine that these two structures evolve in divergent ways. In core–shell nanoparticles, Au atoms from the core migrate outward onto the surface, generating transient “single-atom” Pt active sites with high formic acid oxidation activity. Metal migration continues until Pt is completely encapsulated by Au, and catalytic reactivity ceases. In contrast, AuPt alloys undergo surface dealloying and significant leaching of Pt out of the nanoparticle. Elucidating the dynamic restructuring processes responsible for high electrocatalytic reactivity in Pt bimetallic structures will enable better design and predictive synthesis of nanoparticle catalysts that are both active and stable.

Photocatalytic H2 Evolution from Oxalic Acid: Effect of Cocatalysts and Carbon Dioxide Radical Anion on the Surface Charge Transfer Mechanisms

“…The X-ray photoelectron spectra for Au 2% /TiO 2 and Pt 2% /TiO 2 are presented in Figure S7. Au/TiO 2 exhibits a doublet at 4f 7/2 = 84.2 eV and 4f 5/2 = 87.9 eV, corresponding to the metallic Au nanoparticles (Au 0 ), while Pt/TiO 2 exhibits a doublet at 4f 7/2 = 70.8 eV and 4f 5/2 = 74.1 eV, corresponding to the metallic Pt nanoparticles (Pt 0 ) . Therefore, XPS analysis confirms that both types of nanoparticles are metallic, without a significant presence of oxides.…”

“…Au/TiO 2 exhibits a doublet at 4f 7/2 = 84.2 eV and 4f 5/2 = 87.9 eV, corresponding to the metallic Au nanoparticles (Au 0 ), while Pt/TiO 2 exhibits a doublet at 4f 7/2 = 70.8 eV and 4f 5/2 = 74.1 eV, corresponding to the metallic Pt nanoparticles (Pt 0 ). 16 Therefore, XPS analysis confirms that both types of nanoparticles are metallic, without a significant presence of oxides. Performing the photodeposition under inert atmosphere at pH ≈ 6 using a high concentration of methanol, i.e., 2.7 mol L −1 , would likely result in an almost complete conversion of the metal salts to their metallic state regardless of the loading amount.…”

Synthesis of Au@Pt Core—Shell Nanoparticles as Efficient Electrocatalyst for Methanol Electro-Oxidation

“…The results showed that in presence of CO, Pt diffuses to the surface, allowing the formation of strong Pt-CO bonds [50]. In contrast, when Pt metal is encapsulated by Au (Pt@Au), the catalytic activity diminished due to the CO oxidation does not occur at the cluster surfaces that are initially pure Au [51].…”

Electrochemical Cleaning Stability and Oxygen Reduction Reaction Activity of 1‐2 nm Dendrimer‐Encapsulated Au Nanoparticles

“…[9][10][11][12] It is becoming increasingly clear, however, that these types of pretreatments can significantly alter the properties of the catalysts under study. For example, following pretreatment, structured bimetallic NPs can undergo atomic rearrangements, [13][14][15][16] the crystal structure, shape, and facets can change, [4,[17][18][19] and atoms can undergo selective dissolution. [7,8,13,16,[20][21][22] Even for polycrystalline gold surfaces, the rate of anodic Au dissolution during potential cycling is highly dependent on the surface structure of the electrode.…”