Orientation and morphology of Pt nanoparticles in γ-alumina processed via ion implantation and thermal annealing

Structure and chemistry of metal/metal-oxide interfaces are critical for many catalytic processes and sensing. Pristine interfaces of Pt and γ -Al2O3 were fabricated using high-energy ion implantation and thermal processing. Amorphous regions of alumina develop in single crystal α-alumina during Pt+ implantation and an 800 °C thermal treatment crystalizes amorphized alumina to γ -Al2O3 and allows Pt ions to precipitate within the developing γ -alumina, yielding Pt nanoparticle tetrahedra terminated by {111} surfaces. The phase of alumina that developed and the distribution, morphology, and orientation of Pt nanoparticles was determined using x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy and scanning transmission electron microscopy

First-principles Study of the Products of CO2 Dissociation on Nickel-based Alloys: Trends in Energetics with Alloying Element

Oxidation and corrosion of nickel and Ni-based alloys are a problem for many industrial applications, such as power plants that use supercritical CO2 as the working fluid. In supercritical CO2 environments, CO2 dissociates on the surface forming adsorbed CO and O, which can oxidize the surface. The adsorbed CO can further breakdown via direct CO dissociation or via the Boudouard reaction to form adsorbed C, which can in turn carburize the surface. Understanding how the adsorbed species interact with different Ni-based alloys can help guide the design of future alloys. The interactions of adsorbed O, C, and CO on the (100) and (111) facets of pure Ni and Ni individually alloyed with Al, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ti, V, and W are examined using density functional theory. We find that the binding of CO is energetically similar across all alloy surfaces and both facets, while O binding varies strongly with different metals added to nickel and C binding varies between the different facets but only slightly for different metals alloyed to nickel. The binding of O is weaker on pure Ni and Ni alloyed with Cu, Co, Fe, Al, or Mn and stronger on Ni alloyed with Nb, Cr, Mo, Ti, V, or W, while the binding of C is weaker on the (111) facet than the (100) facet. The difference in the binding energies of the adsorbates across the different alloy surfaces is due mainly to the ensemble effect, rather than the ligand effect. The thermodynamics of CO breakdown are also studied and we find that the breakdown of CO via direct CO dissociation is endothermic on the (111) facet and exothermic on the (100) facet, with the alloy surfaces that bind O strongly having the most exothermic reaction energies. The breakdown of CO via the Boudouard reaction has similar reaction energies across the different alloy surfaces of a single facet and is endothermic on both facets, with the (111) facet being most endothermic. This comprehensive study presents a summary of the current literature as well as a well-rounded view of the products of CO2 breakdown on Ni surfaces alloyed with the most common alloying elements used in industrial applications

In situ X-ray absorption spectroscopy studies of nanoscale electrocatalysts

Nanoscale electrocatalysts have exhibited promising activity and stability, improving the kinetics of numerous electrochemical reactions in renewable energy systems such as electrolyzers, fuel cells, and metal-air batteries. Due to the size effect, nano particles with extreme small size have high surface areas, complicated morphology, and various surface terminations, which make them different from their bulk phases and often undergo restructuring during the reactions. These restructured materials are hard to probe by conventional ex-situ characterizations, thus leaving the true reaction centers and/or active sites difficult to determine. Nowadays, in situ techniques, particularly X-ray absorption spectroscopy (XAS), have become an important tool to obtain oxidation states, electronic structure, and local bonding environments, which are critical to investigate the electrocatalysts under real reaction conditions. In this review, we go over the basic principles of XAS and highlight recent applications of in situ XAS in studies of nanoscale electrocatalysts.Published versio