Balance of Nanostructure and Bimetallic Interactions in Pt Model Fuel Cell Catalysts: In Situ XAS and DFT Study

Abstract

ABSTRACT:We have studied the effect of nanostructuring in Pt monolayer model electrocatalysts on a Rh(111) single-crystal substrate on the adsorption strength of chemisorbed species. In situ high energy resolution fluorescence detection x-ray absorption spectroscopy (HERFD XAS) at the Pt L 3 edge reveals characteristic changes of the shape and intensity of the "white-line" due to chemisorption of atomic hydrogen (H ad ) at low potentials and oxygen-containing species (O/OH ad ) at high potentials. On a uniform, two-dimensional Pt monolayer grown by Pt evaporation in ultrahigh vacuum (UHV), we observe a significant destabilization of both H ad and O/OH ad due to strain and ligand effects induced by the underlying Rh(111) substrate. When Pt is deposited via a wetchemical route, by contrast, three-dimensional Pt islands are formed. In this case, strain and Rh ligand effects are balanced with higher local thickness of the Pt islands as well as higher defect density, shifting H and OH adsorption energies back towards pure Pt. Using density functional theory (DFT) we calculate O adsorption energies and corresponding local ORR activities for fcc threefold hollow sites with various local geometries that are present in the three-dimensional Pt islands.

Electrochemical Oxidation of Size-Selected Pt Nanoparticles Studied Using in Situ High-Energy-Resolution X-ray Absorption Spectroscopy

“…33,35 Moreover, the growth of Pt oxide in the present case is much more rapid. In particular, an almost identical shape of the white line as what is seen with Pt/ Rh(111) at 1.6 V, Figure 3c, is already reached for our sizeselected 1.2 nm NPs at 1.26 V, Figure 3a.…”

Bulk-Palladium and Palladium-on-Gold Electrocatalysts for the Oxidation of Hydrogen in Alkaline Electrolyte

“…Instead, the lower θ Pd/Au found herein points at a galvanic replacement mechanism whereby the reduction of Pd 2+ and the complementing oxidation of a Cu upd -adatom occur at different locations via the donation Table II Figure 3c, and would result in the formation of three-dimensional Pd-islands similar to those obtained upon galvanic replacement of Cu upd with platinum atop Rh(111) single crystals. 71,72 Here it is important to note that the formation of these Pd-islands is not incompatible with the above discussed absence of H-absorption, since the latter is believed to require Pd-thicknesses of ≥ 3 monolayers. 51 Keeping our focus on Figure 7a, the subsequent decrease of the negative potential limit to 0.1 V RHE caused the appearance of reduction currents at ≤ 0.3 V RHE that can be related to the H upd on the Pd-surface, analogous with the behavior observed for Pd PC (cf.…”

Electrochemical Synthesis of Ammonia: A Low Pressure, Low Temperature Approach

“…There is evidence elsewhere in the field of electrochemical catalysis that nanostructured materials result in performance and selectivity enhancements, most notably in the large and growing bodies of literature focused on the development of low-poisoning, high-activity oxygen reduction reaction catalysts and catalysts for methanol electrooxidation. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Lessons learned thus far from theory and experiment point towards the potential successful use of non-precious metals in multi-metallic nanostructured materials for enhanced electrocatalytic performance.…”