ORR and OER on Ni-modified Co3O4(111) Cathodes for Zn-Air Batteries - A Combined Surface Science and Electrochemical Model Study

The performance of structurally and chemically well‐defined Ni‐free and Ni‐modified single‐crystalline Co$_{3}$O$_{4}$(1 1 1) thin‐film electrodes in the oxygen reduction and evolution reactions (ORR and OER) was investigated in a combined surface science and electrochemistry approach. Pure and Ni‐modified Co$_{3}$O$_{4}$(1 1 1) film electrodes were prepared and characterized under ultrahigh‐vacuum conditions by scanning tunneling microscopy and X‐ray photoelectron spectroscopy. Both Ni decoration (by post‐deposition of Ni) and Ni doping (by simultaneous vapor deposition of Ni, Co, and O$_{2}$) induced distinct differences in the base cyclic voltammograms in 0.5 m KOH at potentials higher than 0.7 V compared with Co$_{3}$O$_{4}$ (1 1 1) electrodes. Also, all oxide film electrodes showed a higher overpotential for the ORR but a lower one for the OER than polycrystalline Pt. Ni modification significantly improved the ORR current densities by increasing the electrical conductivity, whereas the OER onset of approximately 1.47 V$_{RHE}$ (RHE: reversible hydrogen electrode) at 0.1 mA cm$^{-2}$ was almost unchanged

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

Hydrogen adsorption on bimetallic PdAu(111) surface alloys:minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

Microscopy and spectroscopy measurements together with periodic DFT calculations provide detailed insight into the adsorption behavior of hydrogen on disordered, but structurally well defined PdAu–Pd(111) surface alloys.</p

Challenges in bimetallic multilayer structure formation: Pt growth on Cu monolayers on Ru(0001)

In a joint experimental and theoretical study, we investigate the formation and morphology of PtCu/Ru(0001) bimetallic surfaces grown at room and higher temperatures under UHV conditions.</p

Blocking Effects on the Hydrogen Oxidation Reaction on Polycrystalline Pt Electrodes

We report differential electrochemical mass spectrometry (DEMS) measurements on blocking effects induced by adsorbed CO or surface oxide on the hydrogen oxidation reaction (HOR) on a polycrystalline Pt electrode, comparing also with earlier results obtained on a thin-film Pt/Vulcan supported catalyst electrode

Growth of an oligopyridine adlayer on Ag(100) - a scanning tunnelling microscopy study

The growth behaviour of the oligopyridine derivative 2-phenyl-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl) pyridine-2-yl) pyrimidine (2,4'-BTP) on Ag(100) in the sub-monolayer regime was investigated by variable temperature scanning tunneling microscopy under ultra-high vacuum conditions. Over the entire coverage range, the molecules are adsorbed in a flat lying configuration, with preferential orientations with respect to the direction of the surface. The azimuth angles are derived using a previously introduced algorithm that fits the positions of the intramolecular N atoms geometrically to the underlying surface lattice ("points-to-lattice fit") [H. E. Hoster et al., Langmuir 2007, 23, 11570], indicating that the orientation of the admolecules and thus of the adllayer structure with respect to the Ag(100) surface lattice is determined by the 2,40-BTP - Ag(100) interaction, while intermolecular interactions are decisive for the structure of the adlayer. The results will be compared to other adsorption systems

Stabilization of large adsorbates by rotational entropy:a time-resolved variable-temperature STM study

Investigating the dynamics in an adlayer of the oligopyridine derivative 2-phenyl-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl)pyridine-2-yl)pyrimidine (2,4'-BTP) on Ag(111) by fast scanning tunneling microscopy (video-STM), we found that rotating 2,4'-BTP adsorbates coexist in a two-dimensional (2D) liquid phase (beta-phase) in a dynamic equilibrium with static adsorbate molecules. Furthermore, exchange between an ordered phase (a-phase) and beta-phase leads to fluctuations of the domain boundary on a time scale of seconds. Quantitative evaluation of the temperature-dependent equilibrium between rotating and static adsorbates, evaluated from a large number of STM images, gains insight into energetic and entropic stabilization and underlines that the rotating adsorbate molecules are stabilized by an entropy contribution, which is compatible with that derived by using statistical mechanics. The general validity of the concept of entropic stabilization of rotating admolecules, favoring rotation already at room temperature, is tested for other typical small, mid-size and large adsorbates

Oxidation of an organic adlayer:a bird's eye view

The reaction of O-2 with an adlayer of the oligopyridine 2-pheny1-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl)pyridine-2-yl)-pyrimidine (2,4'-BTP), adsorbed on the (111) surfaces of silver and gold and on HOPG - which can be considered as a model system for inorganiclorganic contacts - was investigated by fast scanning tunneling microscopy (video STM) and dispersion corrected density functional theory (DFT-D) calculations. Only on Ag(111), oxidation of the 2,4'-BTP adlayer was observed, which is related to the fact that under the experimental conditions O-2 adsorbs dissociatively on this surface leading to reactive 0 adatoms, but not on Au(111) or HOPG. There is a distinct regiospecifity of the oxidation reaction caused by intermolecular interactions. In addition, the oxidation leads to a chiral ordering. The relevance of these findings for reactions involving organic monolayers is discussed

The role of surface defects in large organic molecule adsorption:substrate configuration effects

The role of the configuration of metal surface atoms in the interaction between individual large, planar organic molecules and a metal substrate was investigated by low-temperature scanning tunneling microscopy and density functional theory calculations, including a semi-empirical correction scheme to account for dispersion effects. As test case, we used the adsorption of the oligopyridine derivative 2-phenyl-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl) pyridine-2-yl) pyrimidine (2,4'-BTP) on a stepped Ag(100) surface. Both experiment, via statistical evaluation of the adsorption site and orientation of 2,4'-BTP admolecules, and theory indicate distinct structural effects. The results are compared with the adsorption behavior of pyridine derivatives and benzene on metal surfaces. Consequences on the understanding of the interaction between heteroatoms or functional groups in large organic adsorbates and metal atoms in typical nano-scaled surface defects and hence of the interaction with more realistic metal surfaces are discussed