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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Theory and Simulation of Attractive Nanoparticle Transport in Polymer Melts

We theoretically study the diffusion of a single attractive nanoparticle (NP) in unentangled and entangled polymer melts based on combining microscopic “core–shell” and “vehicle” mechanisms in a dynamic bond percolation theory framework. A physical picture is constructed which addresses the role of chain length (N), degree of entanglement, nanoparticle size, and NP–polymer attraction strength. The nanoparticle diffusion constant is predicted to initially decrease with N due to the dominance of the core–shell mechanism, then to cross over to the vehicle diffusion regime with a weaker N dependence, and eventually plateau at large enough N. This behavior corresponds to decoupling of NP diffusivity from the macroscopic melt viscosity, which is reminiscent of repulsive NPs in entangled melts, but here it occurs for a distinct physical reason. Specifically, it reflects a crossover to a transport mechanism whereby nanoparticles adsorb on polymer chains and diffuse using them as “vehicles” over a characteristic desorption time scale. Repetition of random desorption events then leads to Fickian long time NP diffusion. Complementary simulations for a range of chain lengths and low to moderate NP–polymer attraction strengths are also performed. They allow testing of the proposed diffusion mechanisms and qualitatively support the theoretically predicted dynamic crossover behavior. In conclusion, when the desorption time is smaller than or comparable to the onset of entangled polymer dynamics, the NP diffusivity becomes almost chain length independent.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Crystallization Modes of Poly(3-dodecylthiophene)-Based Block Copolymers Depend on Regioregularity and Morphology

Conjugated block copolymers (BCPs) can self-assemble into highly ordered nanostructures in a melt state. Yet, when cooled below the melting temperature, crystal growth can disrupt the self-assembled structure and produce a poorly ordered fibrillar texture. We determine that crystallization modes of conjugated BCPs based on poly(3-dodecylthiophene) (P3DDT) and poly(2-vinylpyridine) (P2VP) can be tuned through P3DDT regioregularity (RR), as this attribute controls the melting temperature and crystallization rates of P3DDT. When RR is low (7080%), crystallization is observed at temperatures near or below the glass transition of P2VP, so crystal growth is largely confined by the glassy cylindrical or lamellar BCP structure. When RR is high (94%), crystallization occurs at 40 K above the glass transition of P2VP, so there is no longer a restriction of glassy domains. Importantly, crystal growth remains confined by the rubbery P2VP lamellae, but breaks through the rubbery P2VP cylinders. This morphology-dependent behavior is attributed to geometric compatibility of P3DDT crystal growth and the self-assembled symmetry. In a lamellar phase, the P3DDT chain orientations at the P3DDT- block -P2VP interface are compatible with crystal growth, and both the alkyl-stacking and $\pi\pi$ growth directions are unrestricted within a lamellar sheet. In a cylindrical phase, the radial orientation of P3DDT chains at the P3DDT- block -P2VP interface is not compatible with crystal growth, and the hexagonal close-packed symmetry only allows for one direction of unrestricted crystal growth. Significantly, these studies demonstrate that tuning RR of polyalkylthiophenes can open up multiple crystallization modes with the same monomer chemistries and block lengths, thereby decoupling the parameters that govern classical BCP self-assembly and crystal growth.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Based on the elastically collective nonlinear Langevin equation (ECNLE) theory of bulk relaxation in glass-forming liquids, and our recent ideas of how interface-nucleated modification of caging constraints are spatially transferred into the interior of a thick film, we present a force-based theory for dynamical gradients in thick films with one vapor interface that includes collective elasticity effects. Quantitative applications to the foundational hard sphere fluid and polymer melts of diverse fragilities are presented. In this work, we predict a roughly exponential spatial variation of the total activation barrier which is nonperturbatively modified to similar to 10 particle diameters into the film. This leads, to leading order, to the prediction of a reduced alpha relaxation time gradient of a double-exponential form characterized by a nearly constant spatial decay length, in qualitative accord with simulations. The relaxation acceleration at the surface grows exponentially with increasing packing fraction or decreasing temperature. The rate of increase with cooling of the alpha time strongly weakens upon approaching the vapor interface, with the top two layers remaining liquid-like down to similar to ~80-85% of the bulk glass transition temperature. These spatially heterogeneous changes of the temperature variation of the alpha time result in a large and long-range gradient of the local glass transition temperature. An average interfacial layer thickness relevant to ensemble-averaged dielectric and other experiments is also computed. It is predicted to be rather large at the bulk glass transition temperature, decreasing roughly linearly with heating. Remarkably, to leading order the ratio of this layer-averaged interfacial relaxation time to its bulk analogue is invariant to chemistry, volume fraction, and temperature and of modest absolute magnitude. Spatially inhomogeneous power law decoupling of the alpha relaxation time from its bulk value is predicted, with an effective exponent that decays to zero with distance from the free surface in a nearly exponential manner, trends which are in qualitative accord with recent simulations. Finally, this behavior and the double-exponential alpha time gradient are related and can be viewed as consequences of an effective quasi-universal factorization of the total barrier in films into the product of its bulk-temperature-dependent value times a function solely of location in the film.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Entropy and Enthalpy Mediated Segregation of Bottlebrush Copolymers to Interfaces

The composition of polymer blends near interfaces can differ from the average blend composition because the attraction of each polymer toward surfaces is controlled by its chemistry, size, and architecture. In this work, we studied thin film blends of bottlebrush copolymers and linear homopolymers to understand the enthalpic and entropic effects that drive preferential segregation of one constituent to film interfaces. Bottlebrush copolymers containing polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains were blended with either linear PS or linear PMMA, and time-of-flight secondary ion mass spectroscopy was used to quantify the distribution of bottlebrushes through the film thickness as a function of homopolymer type, homopolymer molecular weight, and processing conditions. We found that the bottlebrush copolymers segregated to air and substrate interfaces above a critical molecular weight of the linear homopolymer, consistent with an entropic preference for chain ends and shorter chains toward the interfaces. This segregation was used to tailor the surface wettability of blend films using bottlebrush additives as a minority component. Modeling using self-consistent field theory highlighted effects of conformational entropy and enthalpic interactions in driving almost complete segregation from the interior of the films toward interfaces. Furthermore, enthalpic interactions were predicted to cause lateral phase segregation in cases where the homopolymer is preferred over the bottlebrush copolymer at the substrate, an effect that was also observed in experiments. Finally, this study demonstrates that bottlebrush copolymer additives can be designed to spontaneously segregate to surfaces in thermal blends, providing a possible route to decouple surface properties from bulk properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Twisted MoSe 2 Homobilayer Behaving as a Heterobilayer

Heterostructures (HSs) formed by the transition-metal dichalcogenides materials have shown great promise in next-generation (opto)electronic applications. An artificially twisted HS, allows us to manipulate the optical, and electronic properties. In this work, we introduce the understanding of the energy transfer (ET) process governed by the dipolar interaction in a twisted molybdenum diselenide (MoSe 2 ) homobilayer without any charge-blocking interlayer. We fabricated an unconventional homobilayer (i.e., HS) with a large twist angle by combining the 2 chemical vapor deposition (CVD) and mechanical exfoliation (Exf.) techniques to fully exploit the lattice parameters mismatch and indirect/direct (CVD/Exf.) bandgap nature. These effectively weaken the interlayer charge transfer and allow the ET to control the carrier recombination channels. Our experimental and theoretical results explain a massive HS photoluminescence enhancement due to an efficient ET process. This work shows that the electronically decoupled MoSe 2 homobilayer is coupled by the ET process, mimicking a 'true' heterobilayer nature.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Coherent Spins in van der Waals Semiconductor GeS 2 at Ambient Conditions

Optically active spin defects in van der Waals (vdW) materials have emerged as versatile quantum sensors, enabling applications for a wide range of quantum phenomena in condensed matter systems. Their ease of exfoliation and compatibility with device integration make them promising candidates for future quantum technologies. Here we report the observation and room-temperature coherent control of ensemble spin defects in the high-temperature crystalline phase of germanium disulfide (β-GeS 2 ), a two-dimensional (2D) semiconductor with low nuclear spin density. The defects exhibit spin-1/2 behavior, and their dynamics can be explained by a weakly coupled spin-pair model. We implement dynamical decoupling techniques to extend the coherence time (T 2 ) by a factor of 20. Finally, we use density functional theory (DFT) calculations to estimate the structures and spin densities of two possible spin defect candidates. This work will help to expand the field of quantum sensing with spin defects in 2D materials.

2D materials↗
DOE OSTI2016

Enzymatically Controlled Vacancies in Nanoparticle Crystals

In atomic systems, the mixing of metals results in distinct phase behavior that depends on the identity and bonding characteristics of the atoms. In nanoscale systems, the use of oligonucleotides as programmable “bonds” that link nanoparticle “atoms” into superlattices allows for the decoupling of atom identity and bonding. While much research in atomic systems is dedicated to understanding different phase behavior of mixed metals, it is not well understood on the nanoscale how changes in the nanoscale “bond” affect the phase behavior of nanoparticle crystals. In this work, the identity of the atom is kept the same but the chemical nature of the bond is altered, which is not possible in atomic systems, through the use of DNA and RNA bonding elements. These building blocks assemble into single crystal nanoparticle superlattices with mixed DNA and RNA bonding elements throughout. The nanoparticle crystals can be dynamically changed through the selective and enzymatic hydrolysis of the RNA bonding elements, resulting in superlattices that retain their crystalline structure and habit, while incorporating up to 35% random vacancies generated from the nanoparticles removed. Therefore, the bonding elements of nanoparticle crystals can be enzymatically and selectively addressed without affecting the nature of the atom.

crystals↗
DOE OSTI2019

Significant Phonon Drag Enables High Power Factor in the AlGaN/GaN Two-Dimensional Electron Gas

In typical thermoelectric energy harvesters and sensors, the Seebeck effect is caused by diffusion of electrons or holes in a temperature gradient. However, the Seebeck effect can also have a phonon drag component, due to momentum exchange between charge carriers and lattice phonons, which is more difficult to quantify. In this work, we present the first study of phonon drag in the AlGaN/GaN two-dimensional electron gas (2DEG). We find that phonon drag does not contribute significantly to the thermoelectric behavior of devices with ~100 nm GaN thickness, which suppresses the phonon mean free path. Yet, when the thickness is increased to ~1.2 μm, up to 32% (88%) of the Seebeck coefficient at 300 K (50 K) can be attributed to the drag component. In turn, the phonon drag enables state-of-the-art thermoelectric power factor in the thicker GaN film, up to ~40 mW m –1 K –2 at 50 K. By measuring the thermal conductivity of these AlGaN/GaN films, we show that the magnitude of the phonon drag can increase even when the thermal conductivity decreases. Decoupling of thermal conductivity and Seebeck coefficient could enable important advancements in thermoelectric power conversion with devices based on 2DEGs.

2D electron gas (2DEG)↗
DOE OSTI2026

Relief Zones Enhance the Durability of Ultrathin Membranes in Electrochemical Conversion Devices

Premature failures in electrochemical conversion systems often result when membrane electrode assemblies (MEAs) use ultrathin (≤15 μm-thick) polymer electrolyte membranes, susceptible to mechanical degradation from stress concentrations arising from device-level integration. Herein, relief zones were developed to mitigate mechanical degradation by alleviating excess and nonuniform compression across active areas. Relief zones, created through ablation of carbonaceous diffusion media, enable seamless adaptation across MEA dimensions without need for hardware modifications. Demonstrated using fuel cells as a case study, accelerated stress tests revealed a 6-fold lifetime improvement (∼1500 h) compared to conventional edge-protected MEAs, decoupling device-level engineering effects from material limitations.

accelerated stress test↗
DOE OSTI2018

Aqueous Polysulfide–Air Battery with a Mediator-Ion Solid Electrolyte and a Copper Sulfide Catalyst for Polysulfide Redox

Aqueous sodium polysulfide–air batteries are a promising system for enabling low-cost, high energy density, environmentally benign batteries for grid-scale deployment. However, the sluggish redox kinetics of aqueous polysulfide requires the use of a catalyst. Cobalt sulfide is a traditional catalyst with good activity and stability, but it uses expensive and toxic cobalt. This study demonstrates for the first time the long-term cycling performance of a sodium polysulfide–air battery with a low-cost copper sulfide catalyst for polysulfide redox. Alkaline sodium polysulfide anolyte is paired with an acidic sodium phosphate buffered air catholyte by means of a Na+-ion solid-state electrolyte, which eliminates chemical crossover between the two electrodes while serving as a mediator-ion solid electrolyte. Long-term cycling is achieved by means of a decoupled charge and discharge air electrode. Furthermore, the effect of CuS redox activity in the polysulfide–air voltage window is tested by pre-discharging CuS in LiOH and in NaOH. It was found that the sodium polysulfide–air batteries with CuS catalyst exhibit good cycling performance, with the overpotential only showing a modest increase of 0.09 V after 100 cycles. Batteries assembled with CuS pre-discharged in LiOH exhibit a small boost in performance, while batteries assembled with CuS pre-discharged in NaOH show a small performance decline.

25 ENERGY STORAGE↗
DOE OSTI2020

Nanoscale Engineering of Polymorphism in Cu 2 Se-Based Composites

Crystal polymorphism selection during synthesis is extremely challenging. However, promoting the formation of a specific metastable polymorph enables modulation of the functional properties of phase-change materials through alteration of the relative abundance of various polymorphs. Here, we demonstrate the stabilization of the superionic β-Cu 2 Se phase under ambient conditions and the direct control over the relative ratio between the α-Cu 2 Se and β-Cu 2 Se polymorphs in (x)CuGaSe 2 /(1-x)Cu 2 Se composites using CuGaSe 2 nanoseeds. Here, we found that the small lattice mismatch between β-Cu 2 Se (cubic) and the ab plane of tetragonal CuGaSe 2 nanoseeds promotes the formation of low-energy coherent CuGaSe 2 /β-Cu 2 Se interfaces leading to preferential stabilization of β-Cu 2 Se. Astonishingly, the hierarchical microstructure of the resulting composites enables a remarkable decoupling of charge and heat transport, which is manifested by a breakdown of the Wiedemann-Franz law

36 MATERIALS SCIENCE↗
DOE OSTI2020

Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum Cations

Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones because of their larger specific surface areas and desirable crystal facets. However, often, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures, where SENs deforms into more stable, less active nanoparticles. In this paper, we show that atomic layer deposition (ALD) of Al 2 O 3 at 200 °C can controllably dope Al cations into the shape-engineered CeO 2 nanorods (NRs) to not only increase their shape transition temperature from 400 °C to beyond 700 °C but also greatly increase their specific reversible oxygen storage capacity (srOSC). Furthermore, the substituted Al3+ ions impede the surface diffusion of Ce ions and therefore improve the thermal stability of CeO 2 NRs. These Al3+ dopants form -Al–O–Ce–O– clusters, which are new Ce species and can be reversibly reduced and oxidized at 500–700 °C. This low-temperature chemical doping method decouples the synthesis process of SENs from the doping process and maintains the shape of the SENs during the activation of dopants. This concept could be adopted to enable the applications of other SENs in challenging high-temperature environments.

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

Stability Criteria for Self-Propagating Reaction Waves in Co/Al Multilayers

The propagation of self-sustained formation reactions in sputter-deposited Co/Al multilayers is known to exhibit a design-dependent instability. Multilayers having thin bilayers (<55 nm period) exhibit stable propagating waves, whereas those with a larger period react unstably. The specific two-dimensional (2D) instability observed involves the transverse propagation of a band in front of a stalled front commonly referred to as a “spin band.” Previous finite-element studies have shown that these instabilities are thermodynamically driven by the forward conduction of heat away from the flame front. However, the magnitude of that loss is inherently tied to the bilayer design in traditional bimetallic multilayers, which couples any proposed stability criteria to a varying critical diffusion distance. Here, this work utilizes a recently developed class of materials known as “inert-mediated reactive multilayers” to decouple the thermodynamic and kinetic contributions to propagating wave stability by reducing the stored chemical energy density in normally stable bilayer designs. By depositing an inert product phase (B2-CoAl) within the mid-plane of Co and Al reactant layers, spin instabilities arise as a function of both diluted volume and critical diffusion distance. From there, a stability criterion is determined for Co/Al multilayers based on enthalpy loss from the reaction zone, and its physical significance is explored.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Reactivity of Carbonate Solvent Electrolytes on Lithium Silicon Anodes

Silicon (Si) is promising for lithium-ion battery (LIB) anodes due to their high theoretical capacity and low electrochemical potential. However, significant challenges remain, including severe volumetric expansion during cycling and the electrochemical instability of electrolytes, which leads to the formation of a nonuniform solid electrolyte interphase (SEI). To investigate SEI formation mechanisms, computational molecular dynamics simulations offer valuable insights. In this work, we examine the trajectories and charge transfer behavior of lithium hexafluorophosphate (LiPF 6 ) salt with various solvent compositions using density functional theory (DFT) and ab initio molecular dynamics (AIMD). Among the tested electrolyte systems, LiPF 6 with vinylene carbonate (VC) added to ethyl methyl carbonate (EMC) exhibits the lowest reactivity with the Si anode. In contrast, the effects of fluoroethylene carbonate (FEC) and VC depend on whether the primary solvent is EMC alone or a mixture of ethylene carbonate (EC) and EMC. Moreover, we show that electrolyte reactivity varies with the degree of lithiation of the Si anode (LiSi vs Li 15 Si 4 ) and under different charge states. To decouple electrolyte reactivity from surface effects, we analyze the dissociation and formation energies of individual species from solvated configurations. Overall, these first-principles-based findings provide a strategic foundation for electrolyte design to improve cycling stability and extend calendar life in LIBs using Si anodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Spectroscopic Investigation of the Mechanisms Responsible for the Superior Stability of Hybrid Class 1/Class 2 CO 2 Sorbents: A New Class 4 Category

Hybrid Class 1/Class 2 supported amine CO 2 sorbents demonstrate superior performance under practical steam conditions, yet their amine immobilization and stabilization mechanisms are unclear. Uncovering the interactions responsible for the sorbents’ robust features is critical for further improvements and can facilitate practical applications. We employ solid state 29 Si CP-MAS and 2-D FSLG 1 H– 13 C CP HETCOR NMR spectroscopies to probe the overall molecular interactions of aminosilane/silica, polyamine [poly(ethylenimine), PEI]/silica, and hybrid aminosilane/PEI/silica sorbents. A unique, sequential impregnation sorbent preparation method is executed in a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) setup to decouple amine binding mechanisms at the amine–silica interface from those within bulk amine layers. These mechanisms are correlated with each sorbents’ resistance to accelerated liquid H 2 O and TGA steam treatments (H 2 O stability) and to oxidative degradation (thermal stability). High percentages of CO 2 capture retained (PCR) and organic content retained (OCR) values after H 2 O testing of N-(3-(trimethoxysilyl)propyl)ethylenediamine (TMPED)/PEI and (3-aminopropyl)trimethoxysilane (APTMS)/PEI hybrid sorbents are associated with a synergistic stabilizing effect of the amine species observed during oxidative degradation (thermal gravimetric analysis-differential scanning calorimetry, TGA-DSC). Solid state NMR spectroscopy reveals that the synergistic effect of the TMPED/PEI mixture is manifested by the formation of hydrogen-bonded PEI–NH 2 ···NH 2 –TMPED and PEI–NH 2 ···HO–Si/O–Si–O (TMPED, T 2 ) linkages within the sorbent. DRIFTS further determines that PEI enhances the grafting of TMPED to silica and that PEI is dispersed among a stable network of polymerized TMPED in the bulk, utilizing H-bonded linkages. These findings provide the scientific basis for establishing a Class 4 category for aminosilane/polyamine/silica hybrid sorbents.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2016

Interfacial Octahedral Rotation Mismatch Control of the Symmetry and Properties of SrRuO 3

We can use epitaxial strain to tune the properties of complex oxides with perovskite structure. Beyond just lattice mismatch, the use of octahedral rotation mismatch at heterointerfaces could also provide a route to manipulate material properties. We examine the evolution of the lattice (i.e., parameters, symmetry, and octahedral rotations) of SrRuO 3 films grown on substrates engineered to have the same lattice parameters, but 2 different octahedral rotations. SrRuO 3 films grown on SrTiO 3 (001) (no octahedral rotations) and GdScO 3 -buffered SrTiO 3 (001) (with octahedral rotations) substrates are found to exhibit monoclinic and tetragonal symmetry, respectively. Electrical transport and magnetic measurements reveal that the tetragonal films exhibit higher resistivity, lower magnetic Curie temperatures, and more isotropic magnetism as compared to those with monoclinic structure. Synchrotron-based half-order Bragg peak analysis reveals that the octahedral rotation pattern in both film variants is the same (albeit with slightly different magnitudes of in-plane rotation angles). Furthermore, the abnormal rotation pattern observed in tetragonal SrRuO 3 indicates a possible decoupling between the internal octahedral rotation and lattice symmetry, which could provide new opportunities to engineer thin-film structure and properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanical Properties and Chemical Reactivity of Li x SiO y Thin Films

Silicon (Si) is a commonly studied candidate material for next-generation anodes in Li-ion batteries. A native oxide SiO 2 on Si is often inevitable. However, it is not clear if this layer has a positive or negative effect on the battery performance. This understanding is complicated by the lack of knowledge about the physical properties of the SiO 2 lithiation products and by the convolution of chemical and electrochemical effects during the anode lithiation process. In this study, Li x SiO y thin films as model materials for lithiated SiO 2 were deposited by magnetron sputtering at ambient temperature, with the goal of (1) decoupling chemical reactivity from electrochemical reactivity and (2) evaluating the physical and electrochemical properties of Li x SiO y . X-ray photoemission spectroscopy analysis of the deposited thin films demonstrate that a composition close to previous experimental reports of lithiated native SiO 2 can be achieved through sputtering. Our density functional theory calculations also confirm that the possible phases formed by lithiating SiO 2 are very close to the measured film compositions. Scanning probe microscopy measurements show that the mechanical properties of the film are strongly dependent on lithium concentration, with a ductile behavior at a higher Li content and a brittle behavior at a lower Li content. The chemical reactivity of the thin films was investigated by measuring the AC impedance evolution, suggesting that Li x SiO y continuously reacts with the electrolyte, in part because of the high electronic conductivity of the film determined from solid-state impedance measurements. The electrochemical cycling data of the sputter-deposited Li x SiO y /Si films also suggest that Li x SiO y is not beneficial in stabilizing the Si anode surface during battery operation, despite its favorable mechanical properties.

14 SOLAR ENERGY↗
DOE OSTI2019

Strain Effect on Oxygen Evolution Reaction Activity of Epitaxial NdNiO3 Thin Films

Epitaxial strain can cause both lattice distortion and oxygen non-stoichiometry, effects that are strongly coupled at the heterojunctions of complex nickelate oxides. In this paper, we decouple these structural and chemical effects on the oxygen evolution reaction (OER) using a set of well-defined, coherently-strained epitaxial NdNiO3 (NNO) films. We show that within the regime where oxygen vacancies (VOs) are negligible, compressive strain is favorable for the OER while tensile strain is unfavorable, as the former induces orbital splitting, resulting in a higher occupancy in the orbital and weaker Ni-O chemisorption. However, when the tensile strain is large enough to promote the formation of VOs, an increase in the OER is also observed. The partial reduction of Ni3+ to Ni2+ due to VOs increases the average occupancy of the eg antibonding orbital to more than one, which is believed to account for this increased OER activity. Our work highlights that epitaxial-strain-induced lattice distortion and VO generation can be simultaneously exploited to tune OER activities, of importance for the predictive synthesis of high-performance electrocatalysts.

strain, oxygen vacancy, orbital polarization, meta↗