Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene

The formation of Pt-Ru nanoclusters (NCs) by sequential deposition of Pt and Ru on a periodically rumpled graphene sheet supported on Ru(0001) is analyzed by atomistic-level modeling and kinetic Monte Carlo simulations. The “coarse-scale” periodic variation of the adsorption energy of metal adatoms across the graphene sheet directs the assembly of NCs to a periodic array of thermodynamically preferred locations. The modeling describes not only just the NC densities and size distributions, but also the composition distribution for mixed NCs. A strong dependence of these quantities on the deposition order is primarily related to different effective mobilities of Pt and Ru on the supported graphene

Versatile 3D-Printed Micro-Reference Electrodes for Aqueous and Non-Aqueous Solutions

While numerous reference electrodes suitable for aqueous electrolytes exist, there is no well-defined standard for non-aqueous electrolytes. Furthermore, reference electrodes are often large and do not meet the size requirements for small cells. In this work, we present a simple method for fabricating stable 3D-printed micro-reference electrodes. The prints are made from polyvinylidene fluoride, which is chemically inert in strong acids, bases, and commonly used non-aqueous solvents. We chose six different reference systems based on Ag, Cu, Zn, and Na, including three aqueous and three non-aqueous systems to demonstrate the versatility of the approach. Subsequently, we conducted cyclic voltammetry experiments and measured the potential difference between the aqueous homemade reference electrodes and a commercial Ag/AgCl-electrode. For the non-aqueous reference electrodes, we chose the ferrocene redox couple as an internal standard. From these measurements, we deduced that this new class of micro-reference electrodes is leak-tight and shows a stable electrode potential

Interface Phenomena

This special collection on Interface Phenomena is dedicated to R. Jürgen Behm on the occasion of his retirement and 70th birthday. Jürgen Behm's research over the past 40 years has addressed a wide variety of interface processes in the fields of growth, corrosion, heterogeneous catalysis, electrocatalysis, and batteries

Impact of the potential dependent surface adlayer composition on the ORR activity and H2O2 formation on Ru(0001) in acid electrolytes

Stimulated by the increasing interest in ion adsorption effects on electrocatalytic reactions and by recent more detailed reports on the potential dependent adlayer structures formed on Ru(0001) in pure HClO4 and H2SO4 electrolytes, we revisited the oxygen reduction reaction (ORR) on structurally well-defined Ru(0001) single crystal surfaces prepared under ultrahigh vacuum conditions. We demonstrate that the complex, potential-dependent activity both for the ORR and for H2O2 formation is closely related to potential-dependent changes in the composition and structure of the adlayer. Our results demonstrate the enormous effects adsorbed species can have on the ORR reaction characteristics, either by surface blocking, e.g., by (co-)adsorbed bisulfate species, or by participation in the reaction, e.g., by *H transfer from adsorbed H or OH to O2. The comparison with results obtained on polycrystalline Ru, which differ significantly from Ru(0001) data, furthermore underlines the importance of using structurally well-defined surfaces as a reference system for future theoretical studies

Facet-Dependent Formation and Adhesion of Au Oxide and Nanoporous Au on Poly-Oriented Au Single Crystals

Nanoporous Au has different properties compared to bulk Au, making it an interesting material for numerous applications. Depending on the preparation procedure, the porosity, thickness, and homogeneity of the NPG films can be tuned. To modify the structure of NPG films in a targeted manner and thus adapt them to specific applications, a fundamental understanding of the structure formation is essential. In this work, we focus on NPG prepared from Au oxide formed during high voltage electrolysis in an alkaline electrolyte on a poly-oriented Au single crystal electrode. These poly-oriented single crystals consist of a single crystalline metal bead, with faces with different crystallographic orientations. Consequently, these POSCs allow screening of the influence of the crystallographic orientation on the structure formation of the Au oxide formed during high voltage electrolysis and the NPG film formed via electrochemical reduction of the Au oxide for different facets in a single experiment. The high voltage electrolysis is performed at current densities between 2.70 and 3.76 A / cm² (300 V) and between 0.24 and 6.39 A / cm² (540 V) with electrolysis times ranging from 100 ms to 30 s. The amount of Au oxide formed is determined by electrochemical measurements and the structural properties are investigated by scanning electron microscopy and optical microscopy. We show that the Au oxide formation is mostly independent of the crystallographic orientation except for thick Au oxide layers. In turn, the macroscopic structure of the NPG films depend on the experimental parameters, the thickness of the Au oxide precursor thickness, and the crystallographic orientation of the substrate. Possible reasons for the frequently observed exfoliation of the NPG films are discussed

First Principles Study on the Structural and Magnetic Properties of Low-Index Cu2O and CuO Surfaces

Copper oxides play a crucial role in a wide range of research areas, such as catalysis, photocatalysis, sensing, energy storage, biomedicine, and spintronics. However, further insights into the surface structure and the related magnetic properties of copper oxides are required to improve their performance. Here, we present a computational study on the structural and magnetic properties of low-index Cu2O and CuO surfaces including their bulk oxides based on spin-polarized density functional theory (DFT) via PBE+U and the ab initio atomistic thermodynamics approach. We found that Cu2O surfaces with an excess of oxygen atoms show surface ferromagnetism while CuO surfaces with an excess of copper atoms exhibit surface atoms without a magnetic moment. By analysing the density of states (DOS) and the Bader charges of the surface atoms, we discuss the electronic properties of the copper oxide surfaces and the origin of the observed magnetism. Finally, we derive a correlation between the structure and the magnetic properties of copper oxide surfaces and suggest a possible explanation for the observed magnetism within a simplified model

Nanoporous Au formation on Au substrates via high voltage electrolysis

Nanoporous Au (NPG) films often show distinctly different properties than bare Au electrodes, which make them suitable for various applications in (electro)catalysis or (bio)sensing. A great deal of effort has gone into finding suitable preparation techniques that can be used to target structural properties, such as the pore size or the surface-to-volume ratio. Many of the methods described for preparing these NPG films require complex starting materials such as alloys, multiple synthesis steps, lengthy preparation procedures or a combination of these factors. Here we present an approach that circumvents these difficulties, enabling for a rapid and controlled preparation of NPG films starting from bare Au electrodes. One approach is to prepare in a first step a Au oxide film by high voltage (HV) electrolysis in a KOH solution, which in a second step is reduced either electrochemically or in the presence of H₂O₂. The resulting NPG structures as well as their electrochemically active surface areas strongly depend on the reduction procedure, the concentration and temperature of the H₂O₂-containing KOH solution, as well as the applied voltage and temperature during the HV electrolysis. The NPG film can also be prepared directly by applying electrolysis voltages that result in anodic contact glow discharge electrolysis (aCGDE) over an extended period of time. By carefully adjusting the corresponding parameters, the surface area of the final NPG film can be specifically controlled. The structural properties of the electrodes are investigated by means of XPS, SEM and electrochemical methods

Electroreduction of CO on Polycrystalline Copper at Low Overpotentials

Cu is the only monometallic electrocatalyst to produce highly reduced products from CO₂ selectively because of its intermediate binding of CO. We investigate the performance of polycrystalline Cu for the electroreduction of CO in alkaline media (0.1 M KOH) at low overpotentials (−0.4 to −0.6 V vs RHE). We find that polycrystalline Cu is highly active at these potentials. The overall CO reduction rates are comparable to those of the nanostructured forms of the material, albeit with a distinct product distribution. While nanostructured forms of Cu favor alcohols, polycrystalline Cu produces greater amounts of C₂ and C₃ aldehydes, as well as ethylene