Structure–Property-Performance Relationship of Ultrathin Pd–Au Alloy Catalyst Layers for Low-Temperature Ethanol Oxidation in Alkaline Media

Abstract

Pd-containing alloys are promising materials for catalysis. Yet, the relationship of the structure−property performance strongly depends on their chemical composition, which is currently not fully resolved. Herein, we present a physical vapor deposition methodology for developing Pd x Au 1−x alloys with fine control over the chemical composition. We establish direct correlations between the composition and these materials' structural and electronic properties with its catalytic activity in an ethanol (EtOH) oxidation reaction. By combining X-ray diffraction (XRD) and X-ray photelectron spectroscopy (XPS) measurements, we validate that the Pd content within both bulk and surface compositions can be finely controlled in an ultrathin-film regime. Catalytic oxidation of EtOH on the Pd x Au 1−x electrodes presents the largest forward-sweeping current density for x = 0.73 at ∼135 mA cm −2 , with the lowest onset potential and largest peak activity of 639 A g Pd −1 observed for x = 0.58. Density functional theory (DFT) calculations and XPS measurements demonstrate that the valence band of the alloys is completely dominated by Pd particularly near the Fermi level, regardless of its chemical composition. Moreover, DFT provides key insights into the Pd x Au 1−x ligand effect, with relevant chemisorption activity descriptors probed for a large number of surface arrangements. These results demonstrate that alloys can outperform pure metals in catalytic processes, with fine control of the chemical composition being a powerful tuning knob for the electronic properties and, therefore, the catalytic activity of ultrathin Pd x Au 1−x catalysts. Our highthroughput experimental methodology, in connection with DFT calculations, provides a unique foundation for further materials' discovery, including machine-learning predictions for novel alloys, the development of Pd-alloyed membranes for the purification of reformate gases, binder-free ultrathin electrocatalysts for fuel cells, and room temperature lithography-based development of nanostructures for optically driven processes.

Plasmonic Au–Pd Bimetallic Nanocatalysts for Hot-Carrier-Enhanced Photocatalytic and Electrochemical Ethanol Oxidation

“…EtOH is an attractive nontoxic chemical fuel owing to its existing supply chain, carbon-neutral production from agricultural biomass, high theoretical energy density (~8 kWh•kg −1 ), and simple storage and infrastructure [2,[30][31][32]. Further, the EOR has the capability for H2 generation via catalytic deprotonation under neutral to acidic conditions.…”

“…Breaking the carbon-carbon (C-C) bond has been found to be the rate-limiting step, as the EOR is interrupted by the production of two C2-intermediates: acetaldehyde (CH3CHO, n = 2e − ) first, and then further by acetic acid (CH3COOH, n = 4e − ). The C2-intermediate(s) can obstruct active sites by adsorbing in inactive orientations and possess high energetic barriers for cleaving the C-C bond (>1.0 eV); limiting further oxidation [30,[32][33][34].…”

Emergent Opportunities with Metallic Alloys: From Material Design to Optical Devices

“…As presented in Figure 3h, Au dominates most of the highenergy states in the alloy's dband, whereas comparable contributions from Au and Ag are observed for other states across all critical points of the Brillouin zone. In another work by McClure et al on Au-Pd, [83] the addition of Pd results in strong hybridization close to the Fermi level, with Pd dominating the values and profiles of the additional dbands. Overall, we envision that the DFTbased alloy's band structure calculation and the parametric analysis method could be combined to precisely and efficiently model ε in alloys.…”

“…In another work by McClure et al. on Au–Pd, [ 83 ] the addition of Pd results in strong hybridization close to the Fermi level, with Pd dominating the values and profiles of the additional d‐bands. Overall, we envision that the DFT‐based alloy's band structure calculation and the parametric analysis method could be combined to precisely and efficiently model ε in alloys.…”

Improvement and stabilization of optical hydrogen sensing ability of Au-Pd alloys

“…To handle explosive hydrogen safely, it is important to have a capability to detect it at the very initial stages of small leaks, preferably at sub-ppm levels, and to have a fast rate of detection for monitoring the occurring changes in real time [1][2][3][4][5][6][7][8][9]. Au-Pd alloys and composites will be used to support the needs of future society due to their unique properties well suited for hydrogen storage, hydrogen generation/reaction catalysis, and hydrogen sensing [10][11][12].…”