Abstract
The presence of multiple reactant gases as well as reaction intermediates in a heterogeneous catalytic reaction results in a complex interaction between different components of the catalyst ...with each gas, which can alter the surface and chemical state of the catalyst differently than in the presence of an individual gas alone. In this study, we used
in situ
ambient pressure x-ray photoelectron spectroscopy to study the surface state of Pt/Cu(111) single-atom alloy model system in two catalytically relevant reaction conditions: CO
2
hydrogenation and CO oxidation. We found that the activation of CO
2
results in the formation of CO, which adsorbs on Pt sites at up to 400 K. In the presence of CO
2
and H
2
, Pt catalyzes the reverse water–gas shift reaction, which produces more CO and further stabilizes surface Pt atoms at 450 K. On the other hand, in CO oxidation condition, the presence of O
2
results in the formation of a thick Cu
2
O layer at higher temperatures, and Pt atoms are no longer detected in the surface and subsurface layers. When O
2
is introduced to the sample before CO, the formation of a complete Cu
2
O layer that covers all Pt atoms occurs immediately at room temperature. However, when CO is introduced at room temperature before O
2
, the presence of adsorbed CO on Pt sites stabilizes the surface Pt atoms and prevents the formation of a complete Cu
2
O layer, thus exposing the Pt atoms in ‘holes’ in the Cu
2
O layer.
A difluorobenzoxadiazole building block is synthesized and utilized to construct a conjugated polymer leading to high‐performance thick‐film polymer solar cells with a VOC of 0.88 V and a power ...conversion efficiency of 9.4%. This new building block can be used in many possible polymer structures for various organic electronic applications.
Physical neural networks made of analog resistive switching processors are promising platforms for analog computing. State-of-the-art resistive switches rely on either conductive filament formation ...or phase change. These processes suffer from poor reproducibility or high energy consumption, respectively. Herein, we demonstrate the behavior of an alternative synapse design that relies on a deterministic charge-controlled mechanism, modulated electrochemically in solid-state. The device operates by shuffling the smallest cation, the proton, in a three-terminal configuration. It has a channel of active material, WO
. A solid proton reservoir layer, PdH
, also serves as the gate terminal. A proton conducting solid electrolyte separates the channel and the reservoir. By protonation/deprotonation, we modulate the electronic conductivity of the channel over seven orders of magnitude, obtaining a continuum of resistance states. Proton intercalation increases the electronic conductivity of WO
by increasing both the carrier density and mobility. This switching mechanism offers low energy dissipation, good reversibility, and high symmetry in programming.
The interaction between a catalyst and reactants often induces changes in the surface structure and composition of the catalyst, which, in turn, affect its reactivity. Therefore, it is important to ...study such changes using in situ techniques under well-controlled conditions. We have used ambient pressure X-ray photoelectron spectroscopy to study the surface stability of a Pt/Cu(111) single-atom alloy in an ambient pressure of CO. By directly probing the Pt atoms, we found that CO causes a slight surface segregation of Pt atoms at room temperature. In addition, while the Pt/Cu(111) surface demonstrates poor thermal stability in ultrahigh vacuum conditions, where surface Pt starts to diffuse to the subsurface layer above 400 K, the presence of adsorbed CO enhances the thermal stability of surface Pt atoms. However, we also found that temperatures above 450 K cause restructuring of the subsurface layer, which consequently strengthens the CO binding to the surface Pt sites, likely because of the presence of neighboring subsurface Pt atoms.
The results of kinetic tests and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) show the important role played by a ZnO–copper interface in the generation of CO and the synthesis of ...methanol from CO2 hydrogenation. The deposition of nanoparticles of ZnO on Cu(100) and Cu(111), θoxi < 0.3 monolayer, produces highly active catalysts. The catalytic activity of these systems increases in the sequence: Cu(111) < Cu(100) < ZnO/Cu(111) < ZnO/Cu(100). The structure of the copper substrate influences the catalytic performance of a ZnO–copper interface. Furthermore, size and metal–oxide interactions affect the chemical and catalytic properties of the oxide making the supported nanoparticles different from bulk ZnO. The formation of a ZnO–copper interface favors the binding and conversion of CO2 into a formate intermediate that is stable on the catalyst surface up to temperatures above 500 K. Alloys of Zn with Cu(111) and Cu(100) were not stable at the elevated temperatures (500–600 K) used for the CO2 hydrogenation reaction. Reaction with CO2 oxidized the zinc, enhancing its stability over the copper substrates.
All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important ...contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and energy-dispersive X-ray spectroscopy data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300 °C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500 °C by synchrotron X-ray diffraction. X-ray absorption spectroscopy results indicate the presence of also LaCoO3 in addition to La2Zr2O7 and Li2CO3. On the basis of electrochemical impedance spectroscopy and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500 °C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode|electrolyte interfaces that enable fast Li transfer and high capacity.
The present study examines the synthesis of unique Cu nanostructured model catalysts and their catalytic activity toward CO2 hydrogenation under moderate temperature and pressure reaction conditions. ...Cu-based nanoparticles (NPs) were synthesized by two chemical deposition methods: (1) 5 nm spherical Cu(OH)2 NPs deposited on highly oriented pyrolytic graphite (HOPG) by exposing the HOPG substrate to a colloidal solution of copper, and (2) photocatalytic reduction of Cu(H2O)62+ onto a high density of 15 nm TiO2 NPs grown on HOPG by physical vapor deposition. This photocatalytic reduction results in the deposition of mixed Cu(OH)2 and Cu2O films, while few-nm sized Cu-based NPs are formed on the TiO2 NPs upon subsequent reduction. The chemistry, structure, and morphology of the resulting samples were characterized using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The thermocatalytic activity for the CO2 reduction reaction (CO2RR) under H2 was evaluated with synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and temperature-programmed desorption (TPD) experiments. Several intermediates, including CO2 δ−, HCOO, O–CH3, CO3 2–, CH x , and CO, were observed using AP-XPS. The TiO2 NPs show activity toward the formation of methanol (CH3OH) that occurs mainly through an O–CH3 intermediate. The TiO2 NPs-core–carbon-shell (TiO2@C NPs) shows a clear selectivity toward methane (CH4). The Cu/TiO2 NPs show, however, an activity toward CO, CH4, and CH3OH that depends strongly on the percentage of oxygen present on the Cu NPs surface. This study particularly shows the importance played by the TiO2 NPs for CO2 adsorption and activation and the Cu NPs for H2 and CO2 dissociation. The CO2RR mechanisms are discussed on the basis of the intermediate formation and the surface structure and composition.
Solution processable conjugated organic materials have gained tremendous interest motivated by their potential of low cost, lightweight and especially easy manufacturing of large-area and flexible ...electronics. Toxic halogen-containing solvents have been widely used in the processing of organic electronics, particularly organic photovoltaics (OPVs). To transition this technology to more commercially attractive manufacturing approaches, removing these halogenated solvents remains one of the key challenges. Our morphological (hard/soft X-ray scattering) and calorimetric characterizations reveal that using o-methylanisole, a certified food additive, as processing solvent can achieve similar crystalline properties and domain spacing/purity with that achieved by widely used binary halogenated solvents (chlorobenzene and 1,8-diiodooctane), thus yielding comparable photovoltaic performance in spin-casted films. To move a step forward, we further present the potential of o-methylanisole as processing solvent in the blade-coating of several cases of OPVs in air. Remarkably, this single nonhazardous solvent yields ∼8.4% and ∼5.2% efficiency in OPVs by respectively blade-coating PBDT-TSR:PC71BM and all-polymeric PBDT-TS1:PPDIODT in ambient air, which are among the highest values for the respective kind of device. We postulate this simple nonhazardous solvent approach will also be applicable in the large area roll-to-roll coating and industrial scale printing of high-efficiency OPVs in air.
Li metal batteries using Li metal as negative electrode and LiNi
Mn
Co
O
as positive electrode represent the next generation high-energy batteries. A major challenge facing these batteries is finding ...electrolytes capable of forming good interphases. Conventionally, electrolyte is fluorinated to generate anion-derived LiF-rich interphases. However, their low ionic conductivities forbid fast-charging. Here, we use CsNO
as a dual-functional additive to form stable interphases on both electrodes. Such strategy allows the use of 1,2-dimethoxyethane as the single solvent, promising superior ion transport and fast charging. LiNi
Mn
Co
O
is protected by the nitrate-derived species. On the Li metal side, large Cs
has weak interactions with the solvent, leading to presence of anions in the solvation sheath and an anion-derived interphase. The interphase is surprisingly dominated by cesium bis(fluorosulfonyl)imide, a component not reported before. Its presence suggests that Cs
is doing more than just electrostatic shielding as commonly believed. The interphase is free of LiF but still promises high performance as cells with high LiNi
Mn
Co
O
loading (21 mg/cm
) and low N/P ratio (~2) can be cycled at 2C (~8 mA/cm
) with above 80% capacity retention after 200 cycles. These results suggest the role of LiF and Cs-containing additives need to be revisited.
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