51 Search Results

In this paper, we report on a robust experimental model to investigate strong metal–support interactions (SMSI) and their effect on electrocatalytic reactions in the absence and presence of direct contact between the nanoparticles (NPs) and the metal oxide thin film. Specifically, we describe beneficial interactions between Ni_0.9O thin film supports and PtNPs toward the CO electrooxidation reaction. The metal oxide layer (Ni_0.9O) is prepared by atomic layer deposition and characterized using X-ray photoelectron spectroscopy (XPS). PtNPs, containing an average of either 55 (Pt₅₅) or 140 (Pt₁₄₀) atoms, were synthesized using a dendrimer encapsulation method. The results indicate negative shifts ofmore » ~100 and ~60 mV of the CO electrooxidation peak potential when Ni_0.9O thin films are in contact with Pt₅₅ NPs and Pt₁₄₀ NPs, respectively. Additionally, the oxygen evolution reaction (OER) is suppressed only when the PtNPs are in contact with the Ni_0.9O thin film. Density functional theory (DFT) calculations indicate that both the CO electrooxidation enhancement and suppression of the OER can be attributed to a 1.23 eV decrease of the CO* binding energy and a 0.35 eV increase of the OH* binding energy at a NiO(111)/Pt₅₅ NP interface compared to isolated Pt₅₅ NPs.« less

Abstract Sodiophilic micro‐composite films of sodium‐chalcogenide intermetallics (Na ₂ Te and Na ₂ S) and Cu particles are fabricated onto commercial copper foam current collectors (Na ₂ Te@CF and Na ₂ S@CF). For the first time a controllable capacity thermal infusion process is demonstrated. Enhanced wetting by the metal electrodeposition leads to state‐of‐the‐art electrochemical performance. For example, Na ₂ Te@CF‐based half‐cells demonstrate stable cycling at 6 mA cm ⁻² and 6 mAh cm ⁻² , corresponding to 54 µm of Na electrodeposited/electrodissolved by geometric area. Sodium metal batteries with Na ₃ V ₂ (PO ₄ ) ₃ cathodes are stable at 30C (7 mAmore » cm ⁻² ) and for 10 000 cycles at 5C and 10C. Cross‐sectional cryogenic focused ion beam (cryo‐FIB) microscopy details deposited and remnant dissolved microstructures. Sodium metal electrodeposition onto Na ₂ Te@CF is dense, smooth, and free of dendrites or pores. On unmodified copper foam, sodium grows in a filament‐like manner, not requiring cycling to achieve this geometry. Substrate–metal interaction critically affects the metal–electrolyte interface, namely the thickness and morphology of the solid electrolyte interphase. Density functional theory and mesoscale simulations provide insight into support‐adatom energetics, nucleation response, and early‐stage morphological evolution. On Na ₂ Te sodium atomic dispersion is thermodynamically more stable than isolated clusters, leading to conformal adatom coverage of the surface.« less

Abstract A stable anode‐free all‐solid‐state battery (AF‐ASSB) with sulfide‐based solid‐electrolyte (SE) (argyrodite Li ₆ PS ₅ Cl) is achieved by tuning wetting of lithium metal on “empty” copper current‐collector. Lithiophilic 1 µm Li ₂ Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation during the first charge. The Li ₂ Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous electrodeposition experiments using half‐cells (1 mA cm ⁻² ), the accumulated thickness of electrodeposited Li on Li ₂ Te–Cu is more than 70 µm, which is the thickness of the Li foil counter‐electrode. Full AF‐ASSBmore » with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryogenic focused ion beam (Cryo‐FIB) sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector‐SE interface. Electrodissolution is uniform and complete, with Li ₂ Te remaining structurally stable and adherent. By contrast, an unmodified Cu current‐collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal,” dendrites that extend into SE, and thick non‐uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory (DFT) and mesoscale calculations provide complementary insight regarding nucleation‐growth behavior. Unlike conventional liquid‐electrolyte metal batteries, the role of current collector/support lithiophilicity has not been explored for emerging AF‐ASSBs.« less

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In this work, repeated cold rolling and folding is employed to fabricate a metallurgical composite of sodium–antimony–telluride Na₂(Sb_2/6Te_3/6Vac_1/6) dispersed in electrochemically active sodium metal, termed “NST-Na.” This new intermetallic has a vacancy-rich thermodynamically stable face-centered-cubic structure and enables state-of-the-art electrochemical performance in widely employed carbonate and ether electrolytes. NST-Na achieves 100% depth-of-discharge (DOD) in 1 m NaPF₆ in G2, with 15 mAh cm^–2 at 1 mA cm^–2 and Coulombic efficiency (CE) of 99.4%, for 1000 h of plating/stripping. Sodium-metal batteries (SMBs) with NST-Na and Na₃V₂(PO₄)₃ (NVP) or sulfur cathodes give significantly improved energy, cycling, and CE (>99%). An anode-free batterymore » with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using conventional and cryogenic microscopy (Cryo-EM) indicate that the sodium metal fills the open space inside the self-supporting sodiophilic NST skeleton, resulting in dense (pore-free and solid electrolyte interphase (SEI)-free) metal deposits with flat surfaces. The baseline Na deposit consists of filament-like dendrites and “dead metal”, intermixed with pores and SEI. Density functional theory calculations show that the uniqueness of NST lies in the thermodynamic stability of the Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling.« less

Density functional theory calculations were used to determine the stability of metal slabs consisting of a Pt surface monolayer and intermetallic supporting layers made from combinations of six transition metal elements (Pt, Fe, Co, Ni, Cu, and Ag), as a model system for Pt skin intermetallic core nanoparticle catalysts. The stability of the slabs is largely determined by strain at the interface of the Pt skin and the subsurface intermetallic, which was described by a lattice matching parameter (r). The surface charge on the Pt skin was found to be correlated with the average electronegativity (EN) of the intermetallic core,more » so this average EN was used as a descriptor for how the electronic coupling (or ligand effect) affects adsorption energies. A total of 46 slabs were investigated in terms of their stability, from which 10 stable slabs were selected for further studies of adsorbate binding (OOH*, O*, and OH*) that are intermediates in the oxygen reduction reaction (ORR). The correlation between all three adsorption energies and descriptors r and EN was found. Using a linear fit between our descriptors and the calculated adsorption energies, the overpotential for the ORR was obtained as a function of r and EN, from which a volcano plot was produced. The volcano peak was found at r = 0.96 or at EN = 2.025. Interestingly, neither r nor EN was a sufficient single reactivity descriptor as the data points were well off the general trend in both linear fits; this implies that both the strain effect and the ligand effect influence the adsorption energies, although they are partly correlated. The (r, EN) target peak parameters were used to screen over 241 intermetallic combinations of transition metal elements as active ORR activity. In conclusion, this analysis identified 11 intermetallic compounds which can support a Pt skin to have a high predicted ORR activity.« less

Carbon materials doped with nitrogen and 3d transition metals have attracted a great deal of interest for catalyzing electrochemical reactions such as water splitting, oxygen reduction, and carbon dioxide reduction. Here, we employed density functional theory to study Co–N-doped carbon as electrocatalysts for the oxygen reduction and oxygen evolution reactions. Specifically, we investigated the interplay among adsorption energies, the spin state of the CoN₄ active center, and the applied potential. We found that adsorption energies strongly depend on both the applied potential and the spin state of the Co center. Furthermore, spin state transitions induced by the applied potential alsomore » play an important role in determining the adsorption energies. Here, this effect originates from a different potential of zero charge and capacitance of each spin state.« less

Surfactants are common additives to hydraulic fracturing and enhanced oil recovery (EOR) fluids, and are under consideration for amendment to supercritical carbon dioxide for geological carbon sequestration (GCS). The effect of a common anionic surfactant, internal olefin sulfonate (IOS), on mineral dissolution from shale into brine was evaluated. When added to brine at concentrations exceeding the critical micelle concentration (94 mg/L), IOS inhibited carbonate mineral dissolution in an Eagle Ford shale, as well as dissolution of optical quality calcite (the dominant carbonate in the shale). Laser profilometry images provide spatial resolution across > 3 orders of magnitude, and indicate thatmore » IOS addition to brine both enhances the formation of new etch pits in calcite, and impedes their further growth. Time-of-flight secondary ion mass spectrometry surface profiles show for the first time that IOS preferentially adsorbs at calcite pit edges versus flat calcite surfaces (i.e., terraces). Surface pressure calculations, sulfur K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy results, and density functional theory (DFT) calculations support this observation; the DFT results indicate that the sulfonate head group of the IOS molecule binds strongly to the calcite step site as compared to the terrace site. The S K-edge NEXAFS results indicate that IOS adsorbed more to etched calcite surfaces compared to smooth calcite surfaces. Overall, the results indicate that weak adsorption on flat calcite surfaces (i.e., terraces) disrupts water structure and enhances mass transfer of dissolution, while strong adsorption on calcite pit edges displaces adsorbed water and inhibits further etch pit growth. This work provides the first direct evidence of preferential adsorption of IOS to etched calcite surfaces and links it to macroscopic dissolution kinetics. Finally, this work has implications for surfactant-containing fluids used in hydraulic fracturing, EOR and potentially GCS for subsurface injection into carbonate rich reservoirs.« less

Nitrogen-doped carbon materials are promising metal-free catalysts for the electrochemical oxygen reduction reaction (ORR). A better theoretical understanding on the nature of the active site(s) would help further optimization of their ORR activity. Although quantum mechanical calculations have been widely employed to elucidate the active sites over various catalysts, these calculations are typically done assuming constantcharge conditions rather than the experimentally relevant constant-potential conditions. In this study, we employ the double-reference method to simulate the energetics of the ORR over pure and N-doped carbon materials under constant-potential conditions. We demonstrate that constant-potential calculations enable more accurate theoretical predictions, comparing wellmore » with existing experiments. Our key findings are (1) the zigzag edge of pure graphite is highly active for ORR, (2) the pyridinic N-doped armchair edge is highly active for ORR in alkaline media but not in acid, and (3) graphitic N can donate electrons to pyridinic N to enhance the ORR activity. Furthermore, these fundamental insights provide guidelines for the design of better carbonbased ORR catalysts.« less

Here, we report a robust model for studying electrocatalytic reactions at metal nanoparticles (NPs) in contact with metal oxide surfaces. The metal oxide layer (TiO_x) is prepared by atomic layer deposition, and it is sufficiently thin that it does not hinder electron transfer from the underlying conductive electrode to the supported AuNP electrocatalysts. In advance of the experiments, density functional theory (DFT) predicted that direct contact between AuNPs and TiO_x would lead to enhanced activity for the oxygen reduction reaction (ORR). DFT attributes the observed ORR enhancement to partial charge transfer from oxygen vacancies within the TiO_x film to themore » supported AuNPs and hence formation of anionic Au species. The experimental findings are in near quantitative agreement with the DFT results. Specifically, compared to isolated AuNPs, decreases of ~ 100 and ~ 50 mV in the ORR onset potential are observed experimentally for AuNPs supported on TiO_1.9 and TiO_2.0 films, respectively.« less