Search

The electroreduction of CO2 represents a promising avenue to convert greenhouse gas into valuable fuels and store energy from intermittent renewable sources. Cu-based bimetallic surfaces constitute...

The electronic structure of multimetal, amorphous oxides can be varied across a wide range of elemental compositions. Bulk properties such as conductivity, work function, and absorption can thus be tailored to suit a range of applications spanning from carrier-selective contacts to catalysis. Missing, however, is an understanding of how the surface reactivity is impacted in mixed metal-oxide amorphous films. Here we investigate the propensity of Al(1–x)M(x)Oy (M = Fe, Mn) amorphous oxide films to dissociate water into hydroxyl groups in a humid environment and find comparable hydroxylation at the low relative humidity (∼0.3% RH) probed by ambient pressure X-ray photoelectron spectroscopy. In contrast, films with both Al and Fe show an increased formation of methoxy groups upon methanol exposure compared to pure Al- and Fe-oxide end members, indicating that the coordination environment of the amorphous oxide network impacts the acidity and redox character of surface metal and oxygen sites. These results pr...

Nickel-based catalysts play an important role in the chemical transformation of CO2. A fundamental understanding of the interaction between CO2 and Ni surfaces at atomic level is necessary. In this...

Interactions at the gas–solid interface drive physicochemical processes in many energy and environmental applications; however, the challenges associated with characterization and development of these dynamic interactions in complex systems limit progress in developing effective materials. Therefore, structure–property–performance correlations greatly depend on the development of advanced techniques and analysis methods for the investigation of gas–solid interactions. In this work, adsorption behavior of O2 and humidified O2 on nitrogen-functionalized carbon (N–C) materials was investigated to provide a better understanding of the role of nitrogen species in the oxygen reduction reaction (ORR). N–C materials were produced by solvothermal synthesis and N-ion implantation, resulting in a set of materials with varied nitrogen amount and speciation in carbon matrices with different morphologies. Adsorption behavior of the N–C samples was characterized by in situ diffuse reflectance infrared Fourier-transform ...

Understanding the interaction of CO2 with perovskite metal oxide surfaces is crucial for the design of various perovskite (electro)chemical functionalities, such as solid oxide fuel cells, catalyti...

Understanding how physicochemical properties of materials affect the oxygen evolution reaction (OER) has enormous scientific and technological implications for the OER electrocatalyst design. We pr...

The interface between two functional oxide materials governs the physical, chemical, and electronic interactions between the two phases. We investigate the charge transfer across the interface between two structurally related material classes, namely, perovskite and Ruddlesden–Popper-type oxides, choosing La0.8Sr0.2CoO3−δ (LSC) and Nd2NiO4+δ (NNO) as our model systems for the two classes, respectively. The interface of Nd2NiO4+δ and La0.8Sr0.2CoO3−δ is investigated using in situ photoemission spectroscopy techniques on epitaxial thin films. A detailed analysis of the electronic structure with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy under an oxygen atmosphere and at elevated temperature reveals charge transfer from La0.8Sr0.2CoO3−δ into Nd2NiO4+δ. Through the use of electrical conductivity relaxation, it is demonstrated that such charge transfer from LSC into NNO is accompanied by a reduction in the kinetics of oxygen exchange on Nd2NiO4+δ, contrary to expectation. Fermi level pi...

While model studies of surface science under ultrahigh vacuum (UHV) have made significant contributions to understanding electrochemistry, many issues related to electrochemical phenomena still remain unanswered due to the extreme environmental differences between UHV and liquid conditions. Electrochemical formic acid (HCOOH) oxidation is one such example. While the dehydration step in the indirect oxidation pathway (HCOOH → H2O + COad → 2H+ + 2e– + CO2) is observed in the electrochemical oxidation of formic acid on Pt(111) surface, the surface science studies conducted in UHV condition reported the complete HCOOH dissociation to H2 and CO2 on Pt(111) surface with no adsorbed CO at room temperature. A dehydration mechanism may also exist in gas-phase HCOOH dissociation in some conditions different from UHV, but it has not been demonstrated with a surface science method due to pressure limitations. Using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), we observed the dehydration mechanism of ga...

Nickel carbide and graphene overlayers were grown on Ni(111), which were in situ monitored by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and low energy electron microscopy. CO adsorption and desorption on the formed carbon-modified Ni(111) surfaces were further investigated by NAP-XPS. We found that the carbidic carbon weakens CO adsorption on Ni, resulting in quick CO desorption around room temperature. A full graphene layer on Ni(111) blocks CO adsorption in 10–6 Torr CO, while CO intercalates the graphene overlayers in 0.1 Torr CO at room temperature. On the graphene/CO/Ni(111) surface, the major part of intercalated CO molecules desorbs extensively around 90 °C from the graphene/Ni interface and the remaining part gets trapped under the graphene even at 200 °C. These results suggest that the surface reactivity of a metal catalyst can be strongly modulated by surface carbon structures.

We have conducted in situ measurement of “inverse catalysts” of SnOx nanostructures supported on Pt(111) using ambient-pressure X-ray photoelectron spectroscopy (APXPS) and high-pressure scanning tunneling microscopy (HPSTM) techniques under CO exposure at room temperature and 450 K. Nanostructures of SnOx were prepared by depositing Sn on Pt(111) precovered by O2 layers at liquid nitrogen temperature. APXPS data show that the prepared SnOx nanoparticles are highly reduced, with Sn2+ being the dominant oxide species. The relative Sn2+concentration, compared to Sn4+ and Sn0, in the SnOx nanoparticles decreases slightly with increasing Sn coverage. In situ study of SnOx/Pt(111) inverse catalyst shows that for lower coverage of SnOx (0.25 monolayers (ML)), the amount of Sn2+ decreased steadily, while Sn0 amount steadily increased with negligible Sn4+ amount, as the surface was heated under CO exposure at 450 K. Meanwhile, for the higher coverage (1.0 ML), the decrease of Sn2+ is followed by sharp increase in...

Identifying fundamental barriers that hinder reversible lithium–oxygen (Li–O2) redox reaction is essential for developing efficient and long-lasting rechargeable Li–O2 batteries. Addressing these challenges is being limited by parasitic reactions in the carbon-based O2–electrode with aprotic electrolytes. Understanding the mechanisms of these parasitic reactions is hampered by the complexity that multiple and coupled parasitic reactions involving carbon, electrolytes, and Li–O2 reaction intermediates/products can occur simultaneously. In this work, we employed solid-state cells free of carbon and aprotic electrolytes to probe the influence of surface adventitious hydrocarbons and carbon dioxide (CO2) on the reversibility of the Li–O2 redox chemistry using in situ synchrotron-based ambient pressure X-ray photoelectron spectroscopy. Direct evidence was provided, for the first time, that surface hydrocarbons and CO2 irreversibly react with Li–O2 reaction intermediates/products such as Li2O2 and Li2O, forming...

Ruddlesden–Popper materials such as La2NiO4+δ (LNO) have high activities for surface oxygen exchange kinetics promising for solid oxide fuel cells and oxygen permeation membranes. Here we report the synthesis of the (100)tetragonal-oriented epitaxial LNO thin films prepared by pulsed laser deposition. The surface oxygen exchange kinetics determined from electrochemical impedance spectroscopy (EIS) were found to increase with decreasing film thickness from 390 to 14 nm. No significant change of the surface chemistry with different film thicknesses was observed using ex situ auger electron spectroscopy (AES). Increasing volumetric strains in the LNO films at elevated temperatures determined from in situ high-resolution X-ray diffraction (HRXRD) were correlated with increasing surface exchange kinetics and decreasing film thickness. Volumetric strains may alter the formation energy of interstitial oxygen and influence on the surface oxygen exchange kinetics of the LNO films.

Heterostructured oxide interfaces have demonstrated enhanced oxygen reduction reaction rates at elevated temperatures (∼500–800 °C); however, the physical origin underlying this enhancement is not well understood. By using synchrotron-based in situ ambient pressure X-ray photoelectron spectroscopy (APXPS), we focus on understanding the surface electronic structure, elemental composition, and chemical nature of epitaxial La0.8Sr0.2CoO3−δ (LSC113), (La0.5Sr0.5)2CoO4±δ (LSC214), and LSC214-decorated LSC113 (LSC113/214) thin films as a function of applied electrical potentials (0 to −800 mV) at 520 °C and p(O2) of 1 × 10–3 atm. Shifts in the top of the valence band binding energy and changes in the Sr 3d and O 1s spectral components under applied bias reveal key differences among the film chemistries, most notably in the degree of Sr segregation to the surface and quantity of active oxygen sites in the perovskite termination layer. These differences help to identify important factors governing the enhanced ac...