Voltage effects on the stability of Pd ensembles in Pd-Au/Au(111) surface alloys

The catalytic performance of multimetallic electrodes is often attributed to a beneficial combination of ligand, strain, and ensemble effects. Understanding the influence of the electrochemical environment on the stability of the alloy surface structure is thus a crucial component to the design of highly active and durable electrocatalysts. In this work, we study the effects of an applied voltage to electrocatalytic Pd-Au/Au(111) surface alloys in contact with a model continuum electrolyte. Using planewave density functional theory, two-dimensional cluster expansions are parameterized and used to simulate dilute Pd-Au surface alloys under electrochemical conditions via Metropolis Monte Carlo within an extended canonical ensemble. While Pd monomers are stable at all potentials considered, different extents of surface electrification are observed to promote the formation of Pd dimers and trimers, as well as clusters of Pd monomers. We find that the relative proportion of monomer, dimer, and trimer surface fractions is in good agreement with in situ scanning tunneling microscopy measurements. The further development and refinement of the approaches described herein may serve as a useful aid in the development of next-generation electrocatalysts.

Core–shell and alloy integrating PdAu bimetallic nanoplates on reduced graphene oxide for efficient and stable hydrogen evolution catalysts

PdAu nanoplates with different core–shell structures on rGO were generated by manipulating the competition between galvanic replacement and chemical reduction with the alloy and core–shell integrating nanoplates exhibiting superior HER properties.

Hydrogen evolution reaction on palladium multilayers deposited on Au(111): a theoretical approach

We have investigated the electrocatalytic properties of multilayers of Pd epitaxially deposited on Au(111). In contrast to the numerous previous works in this area, we have focused on the kinetics of the electrochemical step for hydrogen adsorption (Volmer reaction) and determined its energies of activation. We have used a combination of density functional theory calculations and our own theory of electrocatalysis, which allows us to investigate the systems in an electrochemical environment. Contrary to our previous work with a submonolayer of Pd in Au(111), the activation barrier for the hydrogen adsorption process from proton is very low or almost zero for all bimetallic systems investigated. It is about 0.2 eV for pure Pd(111). In the case of two layers of Pd on Au(111) containing absorbed hydrogen in the subsurface, the adsorption free energy is less negative and the barrier lower than for the other investigated systems. This is in agreement with experimental data that shows a larger activity for hydrogen oxidation with hydride Pd systems.

Restructuring of an Ir(210) electrode surface by potential cycling

This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and variations in the electrochemical behaviour after potential cycling of Ir(210) in 0.1 M H2SO4. Faceted structures are obtained electrochemically as a function of time by cycling at a scanrate of 1 V·s(-1) between -0.28 and 0.70 V vs SCE, i.e., between the onset of hydrogen evolution and the surface oxidation regime. The electrochemical behaviour in sulfuric acid solution is compared with that of thermally faceted Ir(210), which shows a sharp characteristic voltammetric peak for (311) facets. Structures similar to thermally-induced faceted Ir(210) are obtained electrochemically, which typically correspond to polyoriented facets at nano-pyramids. These structures grow anisotropically in a preferred direction and reach a height of about 5 nm after 4 h of cycling. The structural changes are reflected in variations of the electrocatalytic activity towards carbon monoxide adlayer oxidation.

Bimetallic alloys in action: dynamic atomistic motifs for electrochemistry and catalysis

Multifarious structural motifs, dynamic surface morphologies and novel reaction mechanisms are essential aspects of bimetallic alloys, making them promising candidates for diverse applications in electrochemistry and heterogeneous catalysis.