Strain Effects on the Oxidation of CO and HCOOH on Au–Pd Core–Shell Nanoparticles

Abstract

The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermediate species only in the case of CS1. This observation allowed us to conclude that the higher activity of CS10 toward this reaction is due to a fast HCOOads oxidation step, probably involving OHads, to generate CO2. Density functional theory calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameter contributing to the change in mechanism is the effective lattice strain.

Formic Acid Oxidation on Pd Thin Film Coated Au Nanocrystals

“…In density functional theory (DFT) calculations, the two effects could be separated by artificially enlarging the lattice constant of the Pd top layer to account for the tensile strain while changing the underneath substrate from Au to Pd to eliminate the ligand effect [19,59]. All of the calculations show that the tensile strain elevates the d-band center and plays a dominant role [19,56,59,60], but there is no consensus on the ligand effect. Roudgar and Groß predicted that the ligand effect further increases the d-band center position [59], while others showed the opposite [19].…”

“…All of the calculations show that the tensile strain elevates the d-band center and plays a dominant role [19,56,59,60], but there is no consensus on the ligand effect. Roudgar and Groß predicted that the ligand effect further increases the d-band center position [59], while others showed the opposite [19]. Nevertheless, the net result is an upshifted d-band center for Pd deposited on Au.…”

Reversible Aqueous Zinc–CO2 Batteries Based on CO2–HCOOH Interconversion

“…[7] Though there have been plenty of electrocatalysts with single functions to aqueous CDRR to HCOOH, [8] and HCOOH oxidation (formic acid oxidation; FAO) to CO 2 in acidic solution, [9] to our knowledge,t he reverse conversion of CO 2 and HCOOH in the same electrolyte has not been realized on abifunctional electrocatalyst. [10] From the perspective of reaction pathways,n eutral CDRR could produce HCOOH via HCOO ad on Pd [11] (where ad = adsorbed) and acidic FAOcould produce CO 2 via HCOO ad on Pd, [12] leading to Pd as apromising candidate material. But the challenge of the electrocatalytic selectivity is that the competitive CO ad formation versus COOH ad occurs in both of CDRR and FAOp rocesses,w hich would decrease the selectivity and stability of Pd catalyst.…”

Gold and gold-palladium branched nanocrystals for applications in plasmonic catalysis and electrocatalysis

“…Because of their unique surface properties, strained nanostructures (for example Au@Pd core-shell) has been used as a more efficient catalyst for electrocatalysis. [72][73][74] After the characterization of nanomaterials, were interested in the investigation of their electrocatalytic activity with and without visible light excitation (plasmonic effects). Considering that the presence of PVP can decrease the electrical conductivity 75 and the blocking the active sites on electrocatalysts surface 76,77 , a method of electrochemical cleaning was proposed based on previous studies.…”

“…87 This effect is not observed for Pd/C electrocatalysts. It is discussed [72][73][74] that the improved catalytic activity in Au@Pd core-shell nanostructures is related to the transfer of SPR-excited charge carriers from Au to the Pd, which can further participate in the electrochemical transformations 89 in which Au can transfer electrons to Pd and facilitate the hot electrons excitation in core-shell nanostructures. This can, in fact, enhance electrocatalytic activity and increase the electrochemical active area (ECSA), as observed in the Table 5.…”