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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Quasi-In-Situ Analysis of Electrode Top Atomic Layers via High-Sensitivity Low-Energy Ion Scattering and Potential-Controlled Sample Transfer

Electrocatalytic reactions involve interfacial interactions between the surfaces of electrodes and reactive species at an electrolyte interface. There are presently no universal or unambiguous methods to directly assay the active top atomic layer composition that influences the reactivity of these electrodes under relevant operating conditions. Low-energy ion scattering (LEIS) spectroscopy is a surface characterization technique that yields compositional analysis of the outermost atomic layer of a material, but it must be performed in ultrahigh vacuum (UHV). Application of LEIS measurements to electrochemical materials that are removed from ambient liquid-phase environments thus leaves an open question as to whether the surface that is transferred to UHV is truly the surface that manifested during the electrochemical reaction. Toward the goal of preserving the active surface state, we developed a sample transfer workflow for LEIS enabling air-free removal and drying of an electrode from an electrochemical cell while maintaining control of the potential using an auxiliary electrode. The potential-controlled emersion method was demonstrated to give distinct potential-dependent surface compositions for a Cu−Pd alloy relative to removal after uncontrolled return to open-circuit potential. A Cu-enriched surface was found at anodic potential and a Pd-enriched surface at cathodic potential, suggesting that the approach can be used to retain representative atomic configurations during transfer. Since adsorbates will often persist from the reaction environment, conventional sample pretreatment methods for removal, including atomic O and atomic H exposure, were also contrasted. Both methods were found to differ with results from incidental low-dose depth profiling by the LEIS primary ion source, which removes adventitious species and surface atoms during the course of repeated measurements. These depth profiles were found to be sensitive to sample history and thus qualitatively informative, despite the possible changes induced by ion damage. The results exhibit (i) the need for complete control over the polarization state of the sample at all times (no excursions to open circuit during transfer) and (ii) the utility of low-dose depth profiling to capture changes in the near-surface composition.

Alloys↗
DOE OSTI2022

Design principles for heterointerfacial alloying kinetics at metallic anodes in rechargeable batteries

How surface chemistry influences reactions occurring thereupon has been a long-standing question of broad scientific and technological interest. Here, we consider the relation between the surface chemistry at interfaces and the reversibility of electrochemical transformations at rechargeable battery electrodes. Using Zn as a model system, we report that a moderate strength of chemical interaction between the deposit and the substrate—neither too weak nor too strong—enables highest reversibility and stability of the plating/stripping redox processes. Focused ion beam and electron microscopy were used to directly probe the morphology, chemistry, and crystallography of heterointerfaces of distinct natures. Analogous to the empirical Sabatier principle for chemical heterogeneous catalysis, our findings arise from competing interfacial processes. Using full batteries with stringent negative electrode–to–positive electrode capacity (N:P) ratios, we show that such knowledge provides a powerful tool for designing key materials in highly reversible battery systems based on Earth-abundant, low-cost metals such as Zn and Na.

25 ENERGY STORAGE↗
DOE OSTI2023

Chromium Tolerant, Highly Active and Stable Electrocatalytic Internal Surface Coating for Cathode of Commercial SOFCs (Final Report)

This project is aimed to develop a chromium (Cr) tolerant, highly active, and stable coating layer on the internal surfaces of the porous composite cathode from commercially available SOFCs. Such coating layer was developed using the additive manufacturing process of Atomic Layer Deposition (ALD) and has been applied on the cathode consisting of either an electronic conductor of LaxSr 1-x MnyO 3-δ (LSM) or mixed ionic and electronic conducting La x Sr 1-x Co y Fe 1-y O 3-δ (LSCF). PI's work has demonstrated that the internal surface of cathode from the commercial cells, can be further tailored using ALD coating to dramatically enhance the cell performance. For instance, ALD layer consisting heterostructured nano composite of nano-Pt and nano-(Mn 0.8 Co 0.2 ) 3 O 4 oxide on the internal surface of porous LSM/YSZ cathode from SOFCs, has resulted in the large reduction of the cell polarizations resistance by up to 53%, and enormous increase of power density over 370%. For the cells with LSCF/Sm 2 O 3 doped CeO 2 (SDC) cathode, the conformal layer of nano-composite consisting of superjacent CoOx and subjacent minimum amount of Pt nano-grains has resulted in the power density enhancement by 126% for the large scale industry tubular cells at 750°C, and both the performance enhancement and nanostructure of the ALD layer are stable over ~ 2000 h continuous operation performed at industry test station. In the meanwhile, those ALD coating layer developed by PI's work is also inherently Cr-tolerant, and could act as physical barrier for preventing Cr diffusion into the cathode backbone, so as to mitigate the Cr poisoning effect on the cathode. In this project, the impact of Cr on the performance of those ALD coated commercial cells has been evaluated. Based on evolution of the cell performance, the ALD coating layer chemistry and ALD coating layer thickness has been optimized to maximize the overall Cr tolerance, cell power density and cell longevity. Different ALD coating has been applied onto the internal surface of LSM/YSZ and LSCF/SDC backbone respectively. The architecture/scaffold structures on the internal surface of different cathode, designed by this project, was catalogued and analyzed using High Resolution Transmission Electron Microscopy (HRTEM), and cell power/durability performance are assured via comprehensive electrochemical performance testing in the industry operation relevant conditions. The impact of the electrochemical operation current density, the water humidity, the cell operation temperature, and cell operation duration on the Cr tolerance of ALD coated cells has been systematically investigated. There is completely different nanostructure degradation mechanisms between LSM and LSCF cells induced by Cr contamination. For the LSCF/SDC baseline cell, With the Cr source, there is no apparent Sr surface segregation phase even for the baseline cell operated for 3000 h at 750 °C. With the Cr source, there is significant amorphous (SrCr)Ox phase accumulated in the original pore region. For the commercial baseline cells, Cr contaminants on the LSM electrode severely impacted the entire cell's electrochemical performance and nanostructure degradation. Those degradations include (1). Peak power density loss of 64 % after 109 h of operation. The dramatic increase in Rp (2). They are cracking at LSM/SSZ interface, LSM grains. SSZ remains intact but with (CrMn)Ox. By contrast, ALD coating (MnCo)Ox/Pt dramatically improves the Cr resistance, as follows (1). ALD-coated cell with a power density is 280-380 % of the baseline cell, depending on the ALD layer thickness. (2). For a cell with a 20 nm thick ALD layer, there is a large performance enhancement (> 200 % power density) induced by ALD coating of Cr-tolerant Mn 0.8 Co 0.2 Ox. (3). For a cell with a 20 nm thick ALD layer, after 168 h at 750 °C power density of the ALD-coated cell is ~ 600% of that baseline cell upon operation with Cr contamination for 109 h. The ALD coating on the internal surface of cathode developed by this project integrated multi-functions. Those multi-functions include (1). Dramatically improving the cell power density for the commercial cells; (2). Dramatically improving contamination resistance of the cathode, for being an excellent protection coating layer sealing off Cr contamination. (3). Dramatically increasing the cell longevity by potentially preventing the microstructure evolution and grain coarsening of the cathode. Overall, this project will provide a simple solution to simultaneously enhance power density and increase the reliability, robustness, and endurance of commercial SOFCs, over the entire operating temperature range of 650-800 °C. For the inherently functional SOFC, the ALD coating of LSM based cathode mitigate the Cr-contamination. Power density of ALD-coated cell is ~ 600% of that baseline cell upon operation with Cr contamination. In addition to SOFCs, the novel on-demand design approach and creation of multifunctional heterogeneous architecture on the electrode surface presented in this work opens further research for their application in other types of fuel cells, batteries, and sensors for which electrochemical reactions on the surface are similarly critical.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Bond Energies of UO + and UC + : Guided Ion Beam and Quantum Chemical Studies of the Reactions of Uranium Cation with O 2 and CO

Here, guided ion beam tandem mass spectrometry was used to examine the kinetic energy dependent reactions of U + with O 2 and CO. In the reaction of U + with O 2 , the UO + product is formed in a barrierless and exothermic process with a reaction efficiency at low energies of k/k col =1.1±0.2, but increases at higher collision energies. Formation of both UO + and UC + in the reaction of U + with CO is endothermic. 0 K bond dissociation energies (BDEs) of D 0 (U + -O)=7.88±0.09 eV and D 0 (U + -C)=4.03±0.13 eV were determined by analyzing the kinetic energy dependent cross sections in the latter endothermic reactions. These values are within experimental uncertainty of previously reported experimental values. Additionally, the electronic states of UO + and UC + and the potential energy surfaces for the reactions were explored by quantum chemical calculations. The former include a full Feller-Peterson-Dixon composite approach with correlation contributions up to CCSDT(Q) for UO and UO + , yielding D 0 (U-O)=7.82 eV and D 0 (U + -O)=7.99 eV, as well as more approximate CCSD(T) calculations where a semi-empirical model was used to estimate spin-orbit energy contributions, which are generally found to improve the agreement with experiment. Both experimental BDEs are observed to be close to those of their transition metal congeners, ScL + , YL + , and GdL + (L=O and C).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mechanism of Chalcophanite Nucleation in Zinc Hydroxide Sulfate Cathodes in Aqueous Zinc Batteries

Aqueous Zn-ion batteries with MnO 2 -based cathodes have seen significant attention owing to their high theoretical capacities, safety, and low cost; however, much debate remains regarding the reaction mechanism that dominates energy storage. In this work, we report our electron microscopy study of cathodes containing zinc hydroxide sulfate (Zn 4 SO 4 (OH) 6 ·xH 2 O, ZHS) together with carbon nanotubes cycled in electrolytes containing ZnSO 4 with varied amounts of MnSO 4 incorporated. The primary Mn-containing phase is formed in situ in the cathode during cycling, where a dissolution-deposition reaction is identified between ZHS and chalcophanite (ZnMn 3 O 7 ·3H 2 O). Mechanistic details of this reaction, in which the chalcophanite nucleates then separates from the ZHS flakes as the ZHS dissolves while acting as the primary Zn source for the reaction, are revealed using surface sensitive methods. Importantly, these findings indicate the reaction is local to the ZHS flakes, providing new insight toward the importance of ZHS and the cathode microstructure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Pt Catalysts Modified with Manganese Oxide through Atomic Layer Deposition for CO Oxidation: Establishing a Coating Layer above or below Pt

The effect of atomic layer deposition (ALD) of manganese oxide on CO oxidation over Pt/Al2O3 is investigated. Two types of catalysts with a thin MnOx layer coated on or under the Pt nanoparticles (NPs) are prepared, and a pristine Pt/Al2O3 catalyst is used as a reference sample. The addition of the ALD layers improves the catalyst durability and both catalysts with MnOx exhibit greater stability after thermal aging at 1073-K. Besides, MnOx promotes CO oxidation through active Pt-MnOx interfacial sites, showing a reaction rate up to 35-fold faster than that of unmodified Pt. Interestingly, the CO adsorption ability of the Pt catalysts with MnOx overcoats is greatly suppressed after the high-temperature calcination; however, the reaction rate of CO oxidation is still excellent. This phenomenon is because the uniformly covered MnOx with two atomic layers diminishes the exposed Pt surface, but the reaction near the Pt-MnOx interfacial site still occurs. Our results guide the effective use of ALD, which is actively applied to heterogeneous catalysis, and provide a novel direction to control metal-assisted interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dissociative electron attachment to 5-bromo-uracil: non-adiabatic dynamics on complex-valued potential energy surfaces

Electron induced dissociation reactions are relevant to many fields, ranging from prebiotic chemistry to cancer treatments. However, the simulation of dissociation electron attachment (DEA) dynamics is very challenging because the auto-ionization widths of the transient negative ions must be accounted for. We propose an adaptation of the ab initio multiple spawning (AIMS) method for complex-valued potential energy surfaces, along the lines of recent developments based on surface hopping dynamics. Our approach combines models for the energy dependence of the auto-ionization widths, obtained from scattering calculations, with survival probabilities computed for the trajectory basis functions employed in the AIMS dynamics. The method is applied to simulate the DEA dynamics of 5-bromouracil in full dimensionality, i.e., taking all the vibrational modes into consideration. The propagation starts on the $π_{2}^{*}$ resonance state and describes the formation of Br - anions mediated by non-adiabatic couplings. The potential energies, gradients and non-adiabatic couplings were computed with the fractional-occupancy molecular orbital complete-active-space configuration-interaction method, and the calculated DEA cross section are consistent with the observed DEA intensities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Facet-dependent structure and dissociation of water at pristine IrO 2 /water interfaces

Understanding the microscopic structure of water at metal oxide interfaces is crucial for advancing electrocatalysis. IrO 2 , specifically, has shown exceptional activity for electrochemical water oxidation, but we currently lack a fundamental understanding of how the surface structure of IrO 2 impacts water reactivity. In this work, we developed a machine learning potential trained to first-principles accuracy for modeling IrO 2 /water interfaces across different facets: (110), (100), (101), and (001). Using extensive machine learning molecular dynamics simulations, we investigated the spontaneous dissociation of water molecules at these interfaces. Our results reveal a distinct dissociation probability trend: (110) > (100) ≈ (101) > (001), which we attribute primarily to the reaction thermodynamics of surface water dissociation. A strong correlation is observed between the surface Ir–O bond distances and the dissociation probabilities, highlighting the role of surface geometry in modulating reactivity. As a consequence, the interfacial solvation structures and hydrogen bonding environments are dynamically tuned by the varying water dissociation capabilities across facets. This work elucidates how water dissociation energetics depend on surface orientation and interfacial structure, offering atomistic insights into manipulating reaction chemistry at electrocatalytic interfaces.

organic↗
DOE OSTI2020

Oxygen evolution reaction over catalytic single-site Co in a well-defined brookite TiO 2 nanorod surface

Efficient electrocatalysts for the oxygen evolution reaction (OER) are paramount to the development of electrochemical devices for clean energy and fuel conversion. However, the structural complexity of heterogeneous electrocatalysts makes it a great challenge to elucidate the surface catalytic sites and OER mechanisms. Here, we report that catalytic single-site Co in a well-defined brookite TiO 2 nanorod (210) surface (Co-TiO 2 ) presents turnover frequencies that are among the highest for Co-based heterogeneous catalysts reported to date, reaching 6.6 ± 1.2 and 181.4 ± 28 s -1 at 300 and 400 mV overpotentials, respectively. Based on grand canonical quantum mechanics calculations and the single-site Co atomic structure validated by in situ and ex situ spectroscopic probes, we have established a full description of the catalytic reaction kinetics for Co-TiO 2 as a function of applied potential, revealing an adsorbate evolution mechanism for the OER. The computationally predicted Tafel slope and turnover frequencies exhibit exceedingly good agreement with experiment.

25 ENERGY STORAGE↗
DOE OSTI2025

Investigation of Electrocatalytic CO 2 Reduction on MXene Materials via First-Principles Simulations

Computational studies of CO 2 reduction to yield various products were carried out on the basal plane and edges of different MXene materials. The impact of vacancies upon Mo 2 TiC 2 T x , W 2 TiC 2 T x , and Ti 3 C 2 T x (T x = O and OH) was also examined for both edge and basal sites. Initial calibrations were carried out to generate surfaces with optimal oxide/hydroxide ratios and proper termination sites upon which various vacancy sites were explored to ensure an accurate model of the surfaces’ resting states. From this work, Mo 2 TiC 2 O was determined to exhibit the lowest theoretical overpotential for methane as determined by volcano plot analyses. At a large enough vacancy concentration, the CO 2 reduction reaction (CO 2 RR) is predicted to outcompete the hydrogen evolution reaction (HER) as the predominant reaction on the surface. In conclusion, when examining the edge of Mo 2 TiC 2 O, stronger CO 2 binding was exhibited to such an extent that the reaction was predicted to terminate after the generation of formate on the edge.

Lund, Colton [Argonne National Laboratory (ANL), A↗
DOE OSTI2024

Node support input to HydroGEN STCH project quarterly report

n this quarter, we further refined our water splitting (WS) reaction calculations on the surface of SrTi 0.5 Mn 0.5 O 3 . Among various surface configurations for WS imposed by surface orientations, terminations, and neighboring chemical species, we hypothesized that (1) the WS reaction energy should be exothermic and (2) the surface oxygen vacancy formation energy should be in a reasonable range compared to the bulk oxygen vacancy formation energy to be accessible during the reduction and WS reaction conditions.

08 HYDROGEN↗
DOE OSTI2025

Selective Hydrogenation of Furfural Acetone over a Cu Catalyst: Combined Theoretical and Experimental Study

The selective hydrogenation of biomass-derived hydroxymethyl furfural (HMF)-acetone-HMF (HAH) presents an alternative route to producing highly functionalized polyesters and polyurethanes. While HAH undergoes furan ring hydrogenation over Pd, Ru, and Ni catalysts, furan ring hydrogenation is not observed over Cu. Herein, we combine reaction kinetics experiments and density functional theory calculations to elucidate the selective hydrogenation behavior of HAH over Cu catalysts. We identified furfural acetone (FAc) as a suitable surrogate for modeling HAH hydrogenation over Cu surfaces and performed reaction kinetics experiments between temperatures of 313–393 K and a H 2 partial pressure of 55 bar. Similar to the behavior of HAH, hydrogenation of FAc follows a consecutive two-step hydrogenation pathway over Cu and does not undergo furan ring hydrogenation. The apparent activation energy barriers for hydrogenation of the aliphatic double bond (0.58 eV) and carbonyl (0.43 eV) of FAc measured in a continuous flow reactor setup are consistent with those reported in prior studies for batch HAH hydrogenation. Reaction orders with respect to each reactant, including H 2 and FAc, were determined to be nearly one. Density functional theory (DFT; GGA-PBE-D3) calculations on Cu(111) showed that the hydrogenation of the aliphatic double bond of FAc is more facile than the hydrogenation of the furan ring, which displays weak interactions with the Cu surface. We determined an apparent activation energy barrier for FAc hydrogenation (0.58 eV) that agreed with our DFT predictions (highest barrier for FAc hydrogenation of 0.57 eV). Finally, our DFT calculations further show that weak interactions between the furan ring and Cu surface are responsible for the selective hydrogenation behavior.

Biomass↗
DOE OSTI2022

The role of alkali metal cations and platinum-surface hydroxyl in the alkaline hydrogen evolution reaction

The platinum-catalysed hydrogen evolution reaction (HER) generally shows poorer kinetics in alkaline electrolyte and represents a key challenge for alkaline water electrolysis. In the presence of alkali metal cations and hydroxyl anions, the electrode–electrolyte (platinum–water) interface in an alkaline electrolyte is far more complex than that in an acidic electrolyte. Here we combine electrochemical impedance spectroscopy and an electrical transport spectroscopy approach to probe and understand the fundamental role of different cations (Li + , Na + and K + ) in HER kinetics. Our integrated studies suggest that the alkali metal cations play an indirect role in modifying the HER kinetics, with the smaller cations being less destabilizing to the hydroxyl adsorbate (OH ad ) species in the HER potential window, which favours a higher coverage of OH ad on the platinum surface. Here, the surface OH ad species are highly polar and act as both electronically favoured proton acceptors and geometrically favoured proton donors to promote water dissociation in alkaline media, thus boosting the Volmer-step kinetics and the HER activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Kinetic description of site ensembles on catalytic surfaces

Significance The kinetic assessment of catalytic reactions is essential to the design and application of thermochemical processes useful in petrochemical synthesis, energy conversion, and environmental remediation. We demonstrate that the ubiquitously used Langmuir–Hinshelwood formalism is incomplete and fails to correctly describe even simple catalytic reactions (e.g., A + A → A 2 ). An accurate kinetic description requires explicit rate equations for multisite configurations (e.g., A*–A* pairs) to account for the nonrandom clustering/isolation of surface species. We rigorously describe clustering/isolation phenomena by derivation of coverage-dependent stoichiometric coefficients, which capture the distinct influence each elementary step exerts on each catalytic site ensemble—thereby overcoming limitations of the mean-field (i.e., Hinshelwood) assumption in describing reactions of mobile Langmuirian adsorbates on catalytic surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ag(111) Remains Significantly Reduced In Situ under Simulated Ethylene Epoxidation Conditions

Direct ethylene epoxidation is among the highest value processes in the chemical industry, yet the reaction mechanism remains debated. A central question is whether the unpromoted Ag catalyst is metallic or oxidized under reaction conditions, as this determines the active oxidant species. Using ambient pressure X-ray photoelectron spectroscopy at chemical potentials simulating industrial conditions, we find that under oxidizing environments, nucleophilic oxygen (∼80% surface coverage) and some carbonate impurities (∼20% coverage) form on Ag(111). Upon switching to an industrially relevant 5:2 ethylene-to-oxygen ratio at 433 K, nucleophilic oxygen is consumed, leaving mostly surface carbonate and bare Ag. The Ag(111) surface maintains ∼50% exposed metallic sites under these conditions. This indicates that proposed mechanisms involving a fully oxidized surface may not represent the state of the surface under relevant reaction conditions and that bare Ag sites, which are necessary to form the oxametallacycle intermediate thought to drive selective epoxidation, are available.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis

Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1–6 nm) by spectroscopically discerning a structure sensitive (CO 2 hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO 2 no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO 2 hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Chemisorbed oxygen or surface oxides steer the selectivity in Pd electrocatalytic propene oxidation observed by operando Pd L-edge X-ray absorption spectroscopy

Controlled electrochemical oxidation of hydrocarbons to desired products is an attractive approach in catalysis. Here we study the electrochemical propene oxidation under operando conditions using Pd L-edge X-ray absorption spectroscopy (XAS) as a sensitive probe to elucidate surface processes occurring during catalysis. Together with ab initio multiple-scattering calculations, our XAS results enable assignment of characteristic changes of the Pd L-edge intensity and energy position in terms of a mechanistic understanding of the selective oxidation of propene. The results, supported by electrochemical density functional theory DFT simulations, show that in the potential range of 0.8–1.0 V vs. the reversible hydrogen electrode (RHE), selective oxidation of propene to acrolein and acrylic acid occurs on the metallic Pd surface. Here, these reactions are proposed to proceed via the Langmuir–Hinshelwood mechanism. In contrast, for the potential range of 1.1–1.3 V vs. RHE, selective oxidation of propene to propylene glycol takes place on a Pd oxide surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗