Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “local”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The Role of Electron Localization in Covalency and Electrochemical Properties of Lithium-Ion Battery Cathode Materials

Following the fundamental research conducted by J. B. Goodenough, the important role of electron localization induced by elemental substitution is studied. The size and electron negativity of host and substituting ions are two important factors in tuning material properties such as local structure and transition metal (TM) oxygen covalency. However, another factor, electron localization, which is widely studied in catalyst research but largely overlooked for battery materials, deserves systematic studies. A combined investigation using synchrotronbased X-ray spectroscopy and theoretical calculations is carried out on the Li-Co-Mn-O model system in which the substituting cation Mn 4+ , with its 3d 3 electronic structure, is used as a promoter for electron localization. Results indicate that electron localization greatly influences the Co - O bond by making it less covalent, which increases the delithiation voltage. It is also found that during charge/discharge, electron localization tends to make TM K-edge X-ray absorption near edge spectroscopy (XANES) spectra show a more “rigid shift” behavior while electron delocalization makes the XANES exhibit a “shape change.” It clearly explains why the K-edge XANES data of some TM oxides show no “rigid shift” while the nominal valence states changed. This work highlights the importance of electron localization with guidance for XANES interpretation.

25 ENERGY STORAGE↗
DOE OSTI2012

Interaction between a plasma membrane-localized ankyrin-repeat protein ITN1 and a nuclear protein RTV1

Highlights: Black-Right-Pointing-Pointer ITN1, a plasma membrane ankyrin protein, interacts with a nuclear DNA-binding protein RTV1. Black-Right-Pointing-Pointer The nuclear transport of RTV1 is partially inhibited by interaction with ITN1. Black-Right-Pointing-Pointer RTV1 can promote the nuclear localization of ITN1. Black-Right-Pointing-Pointer Both overexpression of RTV1 and the lack of ITN1 increase salicylic acids sensitivity in plants. -- Abstract: The increased tolerance to NaCl 1 (ITN1) protein is a plasma membrane (PM)-localized protein involved in responses to NaCl stress in Arabidopsis. The predicted structure of ITN1 is composed of multiple transmembrane regions and an ankyrin-repeat domain that is known to mediate protein-protein interactions. To elucidate the molecular functions of ITN1, we searched for interacting partners using a yeast two-hybrid assay, and a nuclear-localized DNA-binding protein, RTV1, was identified as a candidate. Bimolecular fluorescence complementation analysis revealed that RTV1 interacted with ITN1 at the PM and nuclei in vivo. RTV1 tagged with red fluorescent protein localized to nuclei and ITN1 tagged with green fluorescent protein localized to PM; however, both proteins localized to both nuclei and the PM when co-expressed. These findings suggest that RTV1 and ITN1 regulate the subcellular localization of each other.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

The C-terminal region of Rad52 is essential for Rad52 nuclear and nucleolar localization, and accumulation at DNA damage sites immediately after irradiation

Highlights: •Rad52 might play a key role in the repair of DSB immediately after irradiation. •EYFP-Rad52 accumulates rapidly at DSB sites and colocalizes with Ku80. •Accumulation of Rad52 at DSB sites is independent of the core NHEJ factors. •Localization and recruitment of Rad52 to DSB sites are dependent on the Rad52 CTR. •Basic amino acids in Rad52 CTR are highly conserved among vertebrate species. -- Abstract: Rad52 plays essential roles in homologous recombination (HR) and repair of DNA double-strand breaks (DSBs) in Saccharomyces cerevisiae. However, in vertebrates, knockouts of the Rad52 gene show no hypersensitivity to agents that induce DSBs. Rad52 localizes in the nucleus and forms foci at a late stage following irradiation. Ku70 and Ku80, which play an essential role in nonhomologous DNA-end-joining (NHEJ), are essential for the accumulation of other core NHEJ factors, e.g., XRCC4, and a HR-related factor, e.g., BRCA1. Here, we show that the subcellular localization of EYFP-Rad52(1–418) changes dynamically during the cell cycle. In addition, EYFP-Rad52(1–418) accumulates rapidly at microirradiated sites and colocalizes with the DSB sensor protein Ku80. Moreover, the accumulation of EYFP-Rad52(1–418) at DSB sites is independent of the core NHEJ factors, i.e., Ku80 and XRCC4. Furthermore, we observed that EYFP-Rad52(1–418) localizes in nucleoli in CHO-K1 cells and XRCC4-deficient cells, but not in Ku80-deficient cells. We also found that Rad52 nuclear localization, nucleolar localization, and accumulation at DSB sites are dependent on eight amino acids (411–418) at the end of the C-terminal region of Rad52 (Rad52 CTR). Furthermore, basic amino acids on Rad52 CTR are highly conserved among mammalian, avian, and fish homologues, suggesting that Rad52 CTR is important for the regulation and function of Rad52 in vertebrates. These findings also suggest that the mechanism underlying the regulation of subcellular localization of Rad52 is important for the physiological function of Rad52 not only at a late stage following irradiation, but also at an early stage.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Adipogenesis stimulates the nuclear localization of EWS with an increase in its O-GlcNAc glycosylation in 3T3-L1 cells

Highlights: • The majority of EWS localizes stably in the cytosol in 3T3-L1 preadipocytes. • Adipogenic stimuli induce the nuclear localization of EWS. • Adipogenesis promotes O-GlcNAcylation of EWS. • O-GlcNAcylation stimulates the recruitment of EWS to the nuclear periphery. - Abstract: Although the Ewing sarcoma (EWS) proto-oncoprotein is found in the nucleus and cytosol and is associated with the cell membrane, the regulatory mechanisms of its subcellular localization are still unclear. Here we found that adipogenic stimuli induce the nuclear localization of EWS in 3T3-L1 cells. Tyrosine phosphorylation in the C-terminal PY-nuclear localization signal of EWS was negative throughout adipogenesis. Instead, an adipogenesis-dependent increase in O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation of EWS was observed. Pharmacological inactivation of O-GlcNAcase in preadipocytes promoted perinuclear localization of EWS. Our findings suggest that the nuclear localization of EWS is partly regulated by the glycosylation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

The proper localization of RESPONSIVE TO DESICCATION 20 in lipid droplets depends on their biogenesis induced by STRESS-RELATED PROTEINS in vegetative tissues

Highlights: • The cellular mechanism of SRPs on response to drought stress is proposed. • The mechanism relies on enhancement of LD biogenesis. • RD20 is localized to SRPs-dependent LDs in vegetative tissues. • The enzymatic activity of RD20 is correlated with its LD-localization. Arabidopsis LD surface proteins, SRPs are found only in higher plants and are important for LD biogenesis and abiotic stress signaling. However, the cellular mechanism of SRPs is still unclear. To investigate molecular functions of SRPs, we used tobacco transient expression system. Transient expression of SRPs was sufficient and synergistic for LD biogenesis, and SRPs participated in the formation step of LD in tobacco leaves. RESPONSIVE TO DESICCATION 20 (RD20), a known LD-localizing peroxygenase, localized to LD in the presence of an SRP, and its peroxygenase activity correlated with proper localization of RD20 to LD. Our data suggest that Arabidopsis SRPs play roles as positive factors for LD biogenesis to provide a proper localization of LD-localizing proteins in vegetative tissues.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

The Impact of Definitive Local Therapy for Lymph Node-Positive Prostate Cancer: A Population-Based Study

Purpose: To evaluate the survival outcomes for patients with lymph node-positive, nonmetastatic prostate cancer undergoing definitive local therapy (radical prostatectomy [RP], external beam radiation therapy [EBRT], or both) versus no local therapy (NLT) in the US population in the modern prostate specific antigen (PSA) era. Methods and Materials: The Surveillance, Epidemiology, and End Results database was queried for patients with T1-4N1M0 prostate cancer diagnosed from 1995 through 2005. To allow comparisons of equivalent datasets, patients were analyzed in separate clinical (cN+) and pathologically confirmed (pN+) lymph node-positive cohorts. Kaplan-Meier overall survival (OS) and prostate cancer-specific survival (PCSS) estimates were generated, with accompanying univariate log-rank and multivariate Cox proportional hazards comparisons. Results: A total of 796 cN+ and 2991 pN+ patients were evaluable. Among cN+ patients, 43% underwent EBRT and 57% had NLT. Outcomes for cN+ patients favored EBRT, with 10-year OS rates of 45% versus 29% (P<.001) and PCSS rates of 67% versus 53% (P<.001). Among pN+ patients, 78% underwent local therapy (RP 57%, EBRT 10%, or both 11%) and 22% had NLT. Outcomes for pN+ also favored local therapy, with 10-year OS rates of 65% versus 42% (P<.001) and PCSS rates of 78% versus 56% (P<.001). On multivariate analysis, local therapy in both the cN+ and pN+ cohorts remained independently associated with improved OS and PCSS (all P<.001). Local therapy was associated with favorable hazard ratios across subgroups, including patients aged ≥70 years and those with multiple positive lymph nodes. Among pN+ patients, no significant differences in survival were observed between RP versus EBRT and RP with or without adjuvant EBRT. Conclusions: In this large, population-based cohort, definitive local therapy was associated with significantly improved survival in patients with lymph node-positive prostate cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Detection of Local Cancer Recurrence After Stereotactic Ablative Radiation Therapy for Lung Cancer: Physician Performance Versus Radiomic Assessment

Purpose: Stereotactic ablative radiation therapy (SABR) is a guideline-specified treatment option for early-stage lung cancer. However, significant posttreatment fibrosis can occur and obfuscate the detection of local recurrence. The goal of this study was to assess physician ability to detect timely local recurrence and to compare physician performance with a radiomics tool. Methods and Materials: Posttreatment computed tomography (CT) scans (n=182) from 45 patients treated with SABR (15 with local recurrence matched to 30 with no local recurrence) were used to measure physician and radiomic performance in assessing response. Scans were individually scored by 3 thoracic radiation oncologists and 3 thoracic radiologists, all of whom were blinded to clinical outcomes. Radiomic features were extracted from the same images. Performances of the physician assessors and the radiomics signature were compared. Results: When taking into account all CT scans during the whole follow-up period, median sensitivity for physician assessment of local recurrence was 83% (range, 67%-100%), and specificity was 75% (range, 67%-87%), with only moderate interobserver agreement (κ = 0.54) and a median time to detection of recurrence of 15.5 months. When determining the early prediction of recurrence within <6 months after SABR, physicians assessed the majority of images as benign injury/no recurrence, with a mean error of 35%, false positive rate (FPR) of 1%, and false negative rate (FNR) of 99%. At the same time point, a radiomic signature consisting of 5 image-appearance features demonstrated excellent discrimination, with an area under the receiver operating characteristic curve of 0.85, classification error of 24%, FPR of 24%, and FNR of 23%. Conclusions: These results suggest that radiomics can detect early changes associated with local recurrence that are not typically considered by physicians. This decision support system could potentially allow for early salvage therapy of patients with local recurrence after SABR.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Local Control With 21-Gy Radiation Therapy for High-Risk Neuroblastoma

Purpose: To evaluate local control after 21-Gy radiation therapy (RT) to the primary site in patients with high-risk neuroblastoma. Methods and Materials: After receiving dose-intensive chemotherapy and gross total resection (GTR), 246 patients (aged 1.2-17.9 years, median 4.0 years) with high-risk neuroblastoma underwent RT to the primary site at Memorial Sloan Kettering from 2000 to 2014. Radiation therapy consisted of 21 Gy in twice-daily fractions of 1.5 Gy each. Local failure (LF) was correlated with biologic prognostic factors and clinical findings at the time of diagnosis and start of RT. Results: Median follow-up of surviving patients was 6.4 years. Cumulative incidence of LF was 7.1% at 2 years after RT and 9.8% at 5 years after RT. The isolated LF rate was 3.0%. Eighty-six percent of all local failures were within the RT field. Local control was worse in patients who required more than 1 surgical resection to achieve GTR (22.4% vs 8.3%, P=.01). There was also a trend toward inferior local control with MYCN-amplified tumors or serum lactate dehydrogenase ≥1500 U/L (P=.09 and P=.06, respectively). Conclusion: After intensive chemotherapy and maximal surgical debulking, hyperfractionated RT with 21 Gy in high-risk neuroblastoma results in excellent local control. Given the young patient age, concern for late effects, and local control >90%, dose reduction may be appropriate for patients without MYCN amplification who achieve GTR.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.

36 MATERIALS SCIENCE↗
DOE OSTI2016

HIV-1 nucleocapsid protein localizes efficiently to the nucleus and nucleolus

The HIV-1 nucleocapsid (NC) is an essential viral protein containing two highly conserved retroviral-type zinc finger (ZF) motifs, which functions in multiple stages of the HIV-1 life cycle. Although a number of functions for NC either in its mature form or as a domain of Gag have been revealed, little is known about the intracellular localization of NC and, moreover, its role in Gag protein trafficking. Here, we have investigated various forms of HIV-1 NC protein for its cellular localization and found that the NC has a strong nuclear and nucleolar localization activity. The linker region, composed of a stretch of basic amino acids between the two ZF motifs, was necessary and sufficient for the activity. - Highlights: • HIV-1 NC possess a NLS and leads to nuclear and nucleolus localization. • Mutations in basic residues between two ZFs in NC decrease the nucleus localization. • ZFs of NC affect cytoplasmic organelles localization rather than nucleus localization.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Absolutely Localized Projection-Based Embedding for Excited States

We present a quantum embedding method that allows for calculation of local excited states embedded in a Kohn–Sham density functional theory (DFT) environment. Projection-based quantum embedding methodologies provide a rigorous framework for performing DFT-in-DFT and wave function in DFT (WF-in-DFT) calculations. The use of absolute localization, where the density of each subsystem is expanded in only the basis functions associated with the atoms of that subsystem, provide improved computationally efficiency for WF-in-DFT calculations by reducing the number of orbitals in the WF calculation. In this work, we extend absolutely localized projection-based quantum embedding to study localized excited states using EOM-CCSD-in-DFT and TDDFT-in-DFT. The embedding results are highly accurate compared to the corresponding canonical EOM-CCSD and TDDFT results on the full system, with TDDFT-in-DFT frequently more accurate than canonical TDDFT. The absolute localization method is shown to eliminate the spurious low-lying excitation energies for charge-transfer states and prevent overdelocalization of excited states. Additionally, we attempt to recover the environment response caused by the electronic excitations in the high-level subsystem using different schemes and compare their accuracy. Finally, we apply this method to the calculation of the excited-state energy of green fluorescent protein and show that we systematically converge to the full system results. Here we demonstrate how this method can be useful in understanding excited states, specifically which chemical moieties polarize to the excitation. Furthermore, this work shows absolutely localized projection-based quantum embedding can treat local electronic excitations accurately and make computationally expensive WF methods applicable to systems beyond current computational limits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Revealing Local Structures through Machine-Learning-Fused Multimodal Spectroscopy

Atomistic structures of materials offer valuable insights into their functionality. Determining these structures remains a fundamental challenge in materials science, especially for systems with defects. While both experimental and computational methods exist, each has limitations in resolving nanoscale structures. Core-level spectroscopies, such as X-ray absorption (XAS) or electron energy-loss spectroscopies (EELS), have been used to determine the local bonding environment and structure of materials. Recently, machine learning (ML) methods have been applied to extract structural and bonding information from XAS/EELS data. However, frameworks relying solely on a single data stream, defined as characterization data derived from a single element using one technique, are often insufficient because multiple local environments can yield similar spectral features, making it challenging to differentiate between competing structural hypotheses. Here, in this work, we address this challenge by integrating multimodal ab initio simulations, experimental data acquisition, and ML techniques for structure characterization. Our goal is to determine local structures and properties using EELS and XAS data from multiple elements and edges. To showcase our approach, we use various lithium nickel manganese cobalt (NMC) oxide compounds which are used for lithium ion batteries, including those with oxygen vacancies and antisite defects, as the sample material system. We successfully inferred local element content, ranging from lithium to transition metals, with quantitative agreement with experimental data. Beyond local element inference, we find that ML model based on multimodal spectroscopic data is able to determine whether local defects such as oxygen vacancy and antisites are present, a task which is impossible for single mode spectra or other experimental techniques. Furthermore, our framework is able to provide physical interpretability, bridging spectroscopy with the local atomic and electronic structures.

battery↗
DOE OSTI2024

A Straightforward Model for Quantifying Local pH Gradients Governing the Oxygen Evolution Reaction

The production and consumption of protons by an electrocatalyst will, under certain conditions, generate localized microenvironments with properties distinct from those of the bulk solution. These local properties are particularly impactful for reactions involving proton-coupled electron transfer, where the generation of locally basic or acidic environments may significantly influence the energy efficiency and reaction selectivity of the electrocatalyst. Whereas local pH environments have been observed and characterized in reductive half-reactions, including the CO 2 reduction and hydrogen evolution reactions, the incompatibility of conventional techniques and materials has limited studies in oxidative half-reactions, including the oxygen evolution reaction (OER), which provides the reducing equivalents for solar-to-fuels electrolysis. With the straightforward parameters bulk pH, buffer composition and pK a , and mass transport, we develop a model for describing local pH as a function of current density regardless of the microscopic details of the mechanism. Using an acid-stable PbO x OER catalyst, we observe the formation and dissipation of pH gradients during the OER and validate the model with voltammetric and potentiometric studies. Here, the model predicts how local acidic environments can develop over a narrow OER current density window, thus providing further motivation for the development of OER catalysts that are stable to acid, even when operating in basic aqueous conditions. More generally, the model is not restricted to the OER and is useful for determining the onset of local pH gradients for other electrocatalytic reactions that involve the consumption or generation of protons in energy conversion reactions.

Anions↗
DOE OSTI2024

Expanded Understanding of the Western Antarctic Peninsula Sea‐Ice Environment Through Local and Regional Observations at Palmer Station

Abstract The Western Antarctic Peninsula (WAP) has been experiencing rapid regional warming since at least the 1950s, however, the impacts of this warming at the local scale are variable and nuanced. Previous studies that have linked sea‐ice variability to biogeochemical cycles and food web dynamics often combine local‐scale biogeochemical data with coarse‐resolution regional satellite sea‐ice data, which may not adequately capture local sea‐ice conditions. In this study, we analyzed local‐scale in situ sea‐ice observations collected as part of a 28‐year record (1992–2020) from the Palmer Long‐Term Ecological Research site at Anvers Island, mid‐WAP, in conjunction with isotopically‐derived sea‐ice meltwater (SIM) fractions and satellite‐derived sea‐ice motion and concentration, to quantify the variability and long‐term trends in local sea‐ice behavior. In situ sea ice observations at Palmer Station displayed higher variability than satellite observations and showed no significant declines over this time, despite region‐wide declines identified in prior studies. Higher spring SIM fractions were attributed to strong northward sea‐ice motion throughout the winter. Applying these local‐scale sea‐ice insights to similarly scaled stratification and chlorophyll‐ a measurements, we found that a longer‐lasting, more consistent sea‐ice pack led to greater water column stratification following the spring sea‐ice retreat. Greater sea‐ice persistence and stronger stratification led to larger peaks in chlorophyll‐ a , though sea‐ice metrics did not explain the positive temporal trends in either stratification strength or chlorophyll‐ a . Through this study, we identify how local sea‐ice observations and meltwater data can enhance satellite data to build an understanding of the intricate connections between ice, water column dynamics, and phytoplankton.

Goodell, E.↗
DOE OSTI2023

Emergence of high piezoelectricity from competing local polar order-disorder in relaxor ferroelectrics

Relaxor ferroelectrics are known for outstanding piezoelectric properties, finding a broad range of applications in advanced electromechanical devices. Decoding the origins of the enhanced properties, however, have long been complicated by the heterogeneous local structures. Here, we employ the advanced big-box refinement method by fitting neutron-, X-ray-based total scattering, and X-ray absorption spectrum simultaneously, to extract local atomic polar displacements and construct 3D polar configurations in the classical relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 . Our results demonstrate that prevailing order-disorder character accompanied by the continuous rotation of local polar displacements commands the composition-driven global structure evolution. The omnidirectional local polar disordering appears as an indication of macroscopic relaxor characteristics. Combined with phase-field simulations, it demonstrates that the competing local polar order-disorder between different states with balanced local polar length and direction randomness leads to a flattening free-energy profile over a wide polar length, thus giving rise to high piezoelectricity. Our work clarifies that the critical structural feature required for high piezoelectricity is the competition states of local polar rather than relaxor.

42 ENGINEERING↗
DOE OSTI2023

Three-dimensional atomic structure and local chemical order of medium- and high-entropy nanoalloys

Medium- and high-entropy alloys (M/HEAs) mix several principal elements with near-equiatomic composition and represent a model-shift strategy for designing previously unknown materials in metallurgy, catalysis and other fields. One of the core hypotheses of M/HEAs is lattice distortion, which has been investigated by different numerical and experimental techniques. However, determining the three-dimensional (3D) lattice distortion in M/HEAs remains a challenge. Moreover, the presumed random elemental mixing in M/HEAs has been questioned by X-ray and neutron studies, atomistic simulations, energy dispersive spectroscopy and electron diffraction, which suggest the existence of local chemical order in M/HEAs. However, direct experimental observation of the 3D local chemical order has been difficult because energy dispersive spectroscopy integrates the composition of atomic columns along the zone axes and diffuse electron reflections may originate from planar defects instead of local chemical order. Here, in this work, we determine the 3D atomic positions of M/HEA nanoparticles using atomic electron tomography and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order (CSRO). We find that the high-entropy alloys have larger local lattice distortion and more heterogeneous strain than the medium-entropy alloys and that strain is correlated to CSRO. We also observe CSRO-mediated twinning in the medium-entropy alloys, that is, twinning occurs in energetically unfavoured CSRO regions but not in energetically favoured CSRO ones, which represents, to our knowledge, the first experimental observation of correlating local chemical order with structural defects in any material. We expect that this work will not only expand our fundamental understanding of this important class of materials but also provide the foundation for tailoring M/HEA properties through engineering lattice distortion and local chemical order.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Direct observation of the local microenvironment in inhomogeneous CO 2 reduction gas diffusion electrodes via versatile pOH imaging

In this study, we report how the micrometer-scale morphology of a carbon dioxide reduction (CO 2 R) gas diffusion electrode (GDE) affects the mass transport properties and with it, the local CO 2 R performance. We developed a technique to probe the microenvironment in a CO 2 R GDE via local pOH imaging with time- and three-dimensional spatial, micrometer-scale resolution. The local activity of hydroxide anions (OH - ), represented by the pOH value, around a GDE in contact with an aqueous electrolyte is a crucial parameter that governs the catalytic activity and CO 2 R selectivity. Here, we use fluorescence confocal laser scanning microscopy (CLSM) to create maps of the local pOH around a copper GDE by combining two ratiometric fluorescent dyes, one of which is demonstrated as a pOH sensor for the first time in this work. We observe that the local pOH decreases when current is applied due to the creation of OH - as a byproduct of CO 2 R. Interestingly, the pOH is lower inside microtrenches compared to the electrode surface and decreases further as trenches become more narrow due to enhanced trapping of OH - . We support our experimental results with multiphysics simulations that correlate exceptionally well with measurements. These simulations additionally suggest that the decreased pOH inside microcavities in the surface of a CO 2 R GDE leads to locally enhanced selectivity towards multicarbon (C 2+ ) products. This study suggests that narrow microstructures on the length scale of 5 μm in a GDE surface serve as local CO 2 R hotspots, and thus highlights the importance of a GDE's micromorphology on the CO 2 R performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

On the separability of the extended molecule: Constructing the best localized molecular orbitals for an organic molecule bridging two model electrodes

Based on a quantum chemical valence formalism that allows the rigorous construction of best-localized molecular orbitals on specific parts of an extended system, we examined the separability of individual components of model systems relevant to the description of electron transport in molecular devices. We started by examining how to construct the maximally localized electronic density at the tip of a realistic model of a gold electrode. By varying the number of gold atoms included in the local region where to project the total electronic density, we quantitatively assess how many molecular orbitals are entirely localized in that region. We then considered a 1,4-benzene-di-thiol molecule connected to two model gold electrodes and examined how to localize the electronic density of the total system in the extended molecule, a fractional entity comprising the organic molecule plus an increasing number of the closest metal atoms. We were able to identify in a rigorous manner the existence of three physically different electronic populations, each one corresponding to a distinct set of molecular orbitals. First, there are those entirely localized in the extended molecule, then there is a second group of those completely distributed in the gold atoms external to that region, and, finally, there are those delocalized over the entire system. This latter group can be associated to the shared electronic population between the extended molecule and the rest of the system. We suggest that the treatment here presented could be useful in the theoretical analysis of the electronic transport in nanodevices whenever the use of localized molecular states are required by the physics of the specific problem, such as in cases of weak coupling and super-exchange limits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗