Search NASA⌕ Search

SEARCH · Search NASA

Results for “FAC”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Identification and In-vivo Characterization of a Novel OhrR Transcriptional Regulator in Burkholderia xenovorans LB400

Transcriptional regulators (TRs) are an important and versatile group of proteins, yet very little progress has been achieved towards the discovery and annotation of their biological functions. We have characterized a previously unknown organic hydroperoxide resistance regulator from Burkholderia xenovoransLB400, Bxe_B2842, which is homologous to E. coli’s OhrR. Bxe_B2842 regulates the expression of an organic hydroperoxide resistance protein (OsmC). We utilized frontal affinity chromatography coupled with mass spectrometry (FAC-MS) and electrophoretic mobility gel shift assays (EMSA) to identify and characterize the possible effectors of the regulation by Bxe_B2842. Without an effector, Bxe_B2842 binds a DNA operator sequence (DOS) upstream of osmC. FAC-MS results suggest that 2-aminophenol binds to the protein and is potentially an effector molecule. EMSA analysis shows that 2-aminophenol also attenuates the Bxe_B2842’s affinity for its DOS. EMSA analysis also shows that organic peroxides attenuate Bxe_B2842/DOS affinity, suggesting that binding of the TR to its DOS is regulated by the two-cysteine mechanism, common to TRs in this family. Bxe_B2842 is the first OhrR TR to have both oxidative and effector-binding mechanisms of regulation. Our paper reveals further mechanistic diversity TR mediated gene regulation and provides insights into methods for function discovery of TRs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Test Plan for Reirradiation and 1400°C Heating Test of AGR-3/4 Compact 10-1

Post irradiation examination (PIE) and heating tests of tristructural isotropic (TRISO)-coated fuel particles, fuel compacts, and graphite from Advanced Gas Reactor (AGR) irradiation experiment AGR 3/4 are in progress. The AGR-3/4 test train consisted of twelve separate capsules irradiated in the northeast flux trap of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) from December 14, 2011, to April 12, 2014 (Collin 2015b). This test plan describes the reirradiation and subsequent heating test of AGR-3/4 Compact 10-1. One of the main goals of this test is to assess the retention of short-lived fission products I-131 (t1/2 = 8.02 d) and Xe-133 (t1/2 = 5.2 d) in fuel kernels. To generate short-lived fission products, the compact will first be reirradiated in the Neutron Radiography Reactor (NRAD). Following reirradiation, the compact will be removed from NRAD, gamma scanned on the Precision Gamma Scanner (PGS), and then loaded into the Fuel Accident Condition Simulator (FACS) furnace for heating at 1400°C. Fission gases and condensable fission products released from the compact will be collected in the Fission Gas Monitoring System (FGMS) and the FACS condensation plates, respectively.

42 ENGINEERING↗
DOE OSTI2019

Test Plan for Reirradiation and 1600°C Heating Test of AGR-3/4 Compact 3-1

Post irradiation examination (PIE) and heating tests of tristructural isotropic (TRISO)-coated fuel particles, fuel compacts, and graphite from Advanced Gas Reactor (AGR) irradiation experiment AGR 3/4 are in progress. The AGR-3/4 test train consisted of twelve separate capsules irradiated in the northeast flux trap of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) from December 14, 2011, to April 12, 2014 (Collin 2015b). This test plan describes the reirradiation and subsequent heating test of AGR-3/4 Compact 3-1. One of the main goals of this test is to assess the retention of short-lived fission products I-131 (t1/2 = 8.02 d) and Xe-133 (t1/2 = 5.2 d) in fuel kernels. To generate short-lived fission products, the compact will first be reirradiated in the Neutron Radiography Reactor (NRAD). Following reirradiation, the compact will be removed from NRAD, gamma scanned on the Precision Gamma Scanner (PGS), and then loaded into the Fuel Accident Condition Simulator (FACS) furnace for heating at 1600°C. Fission gases and condensable fission products released from the compact will be collected in the Fission Gas Monitoring System (FGMS) and the FACS condensation plates, respectively. The planned uses of AGR-3/4 compacts (including heating testing and destructive analysis) are discussed in the AGR-3/4 PIE plan (Demkowicz 2017).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Test Plan for the 1400°C Heating Test of AGR-3/4 Compact 8-2

Post irradiation examination (PIE) and heating tests of tristructural isotropic (TRISO)-coated fuel particles, fuel compacts, and graphite from Advanced Gas Reactor (AGR) irradiation experiment AGR 3/4 is in progress. The AGR-3/4 test train consisted of twelve separate capsules irradiated in the northeast flux trap of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) from December 14, 2011, to April 12, 2014 (Collin 2015). This test plan describes the heating test of AGR-3/4 Compact 8-2. The test will involve heating the compact in the Fuel Accident Condition Simulator (FACS) furnace to a peak temperature of 1400°C while collecting fission products released from the compact for subsequent analysis. One of several features of AGR-3/4 that set it apart from AGR-1 and AGR-2 is the incorporation of 20 designed-to-fail (DTF) particles in each compact. The fuel kernels in the DTF particles were coated only with a thin (20 µm thick) pyrocarbon layer having high anisotropy such that the coating would most-likely fail during the irradiation, resulting in up to 20 exposed kernels per compact. One of the main goals of this test is to assess the retention of fission products in the exposed kernels and the surrounding graphitic matrix material comprising the compact. Future heating tests will expose a number of AGR-3/4 compacts at different temperatures in the FACS furnace (Demkowicz 2017). Additionally, the ability may be developed to heat re-irradiated AGR-3/4 compacts to allow a determination of the retention of short-lived fission products I-131 and Xe-133.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Test Plan for the 1200°C Heating Test of AGR-3/4 Compact 10-2

Post irradiation examination (PIE) and heating tests of tristructural isotropic (TRISO)-coated fuel particles, fuel compacts, and graphite from Advanced Gas Reactor (AGR) irradiation experiment AGR 3/4 is in progress. The AGR-3/4 test train consisted of twelve separate capsules irradiated in the northeast flux trap of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) from December 14, 2011, to April 12, 2014 (Collin 2015). This test plan describes the heating test of AGR-3/4 Compact 10-2. The test will involve heating the compact in the Fuel Accident Condition Simulator (FACS) furnace to a peak temperature of 1200°C while collecting fission products released from the compact for subsequent analysis. One of several features of AGR-3/4 that set it apart from AGR-1 and AGR-2 is the incorporation of 20 designed-to-fail (DTF) particles in each compact. The fuel kernels in the DTF particles were coated only with a thin (20 µm thick) pyrocarbon layer having high anisotropy such that the coating would most-likely fail during the irradiation, resulting in up to 20 exposed kernels per compact. One of the main goals of this test is to assess the retention of fission products in the exposed kernels and the surrounding graphitic matrix material comprising the compact. Future heating tests will expose a number of AGR-3/4 compacts at different temperatures in the FACS furnace (Demkowicz 2017). Additionally, the ability may be developed to heat re-irradiated AGR-3/4 compacts to allow a determination of the retention of short-lived fission products I-131 and Xe-133.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Utility of anthesis–silking interval information to predict grain yield under water and nitrogen limited conditions

Delayed silking relative to pollen shed, measured as the anthesis–silking interval (ASI, the period between pollen shed and silking), is a good indicator of response to abiotic stresses in maize ( Zea mays L.). This research was conducted to investigate how ASI is affected by nitrogen (N) and water availability and to assess the utility of ASI to indirectly predict grain yield (GY) under contrasting water and N treatments. Two experiments were conducted in Hancock, WI, in 2018 and 2019. One experiment (Diverse hybrids) included 302 hybrids resulting from the cross of diverse inbred lines by a single tester evaluated at four different treatment levels resulting from combining nonlimited and low N with nonlimited and low water treatments. The second experiment (NSS FAC) included a set of 408 hybrids derived from the cross of biparental doubled-haploid lines from 13 factorial populations and evaluated under nonlimited and low N treatments. Anthesis and silk time in growing degree days, and GY (Mg ha -1 ) were measured. Genomic prediction was assessed using a genomic best linear unbiased prediction model, and predictive ability was calculated as the correlation between genomic predictions and adjusted means in the different treatments. Predictive ability ranged from .15 to .49 for NSS FAC and from .06 to .51 for Diverse hybrids across traits and treatments. The ASI was a good indicator of stress and showed higher heritability than GY in the limited treatments for both experiments; however, it did not improve yield predictability.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Distribution of solutions of the fastest apparent convergence condition in optimized perturbation theory and its relation to anti-Stokes lines

We discuss fundamental properties of the fastest apparent convergence (FAC) condition which is used as a variational criterion in optimized perturbation theory (OPT). We examine an integral representation of the FAC condition and a distribution of the zeros of the integral in a complex artificial parameter space on the basis of theory of Lefschetz thimbles. We find that the zeros accumulate on a certain line segment known as an anti-Stokes line in the limit K→∞, where K is a truncation order of a perturbation series. This phenomenon gives an underlying mechanism that physical quantities calculated by OPT can be insensitive to the choice of the artificial parameter.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Signatures of substorm related overshielding electric field at equatorial latitudes under steady southward IMF Bz during main phase of magnetic storm

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. Here, in this work, interesting observations of the strong westward electric field in the day side equatorial latitudes are presented, as evidenced by strong Counter Electrojet (CEJ) at Indian and Japanese sectors under the steady southward IMF Bz. The westward electric field perturbations are quite large with CEJ amplitude of ~-120 nT over the Indian sector (14–15 December 2006) and ~-220 nT for Japanese sector (7–8 November 2004). The plausible mechanisms for the observed overshielding electric fields under steady southward IMF Bz have been investigated in light of the possible role of substorm activity. The clear signatures of substorm were observed at geosynchronous particle flux measurements from LANL (Los Alamos National Laboratory) satellite and associated with sudden decrease in AL index. The observed variations of asymmetric ring current shows the enhancement of Partial Ring Current (PRC) at the dusk sector further supporting the substorm onset during that period which will probably enhance the overshielding due to increased Region 2 Field-Aligned Currents (R2 FACs). Finally, the observations of such significantly large amplitudes of CEJ associated with the substorm related overshielding events are sparse and the results bring out the important role of substorm onset and the development of PRC in accordance with the R2 FACs during intense magnetic storms which alter the day time equatorial electric field perturbations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Effects of intracellular iron overload on cell death and identification of potent cell death inhibitors

Highlights: • Ferric ammonium citrate induced intracellular iron overload causes ferroptosis. • Protein 3-phosphoinositide-dependent kinase 1 inhibitor GSK2334470 is a potent ferroptosis inhibitor. • Iron/8-hydroxyquinoline complex induced intracellular iron overload partially activates parthanatos. • Plenty of phenolic compounds prevent Fe-8HQ induced cell death by scavenging reactive oxygen species. Iron overload causes many diseases, while the underlying etiologies of these diseases are unclear. Cell death processes including apoptosis, necroptosis, cyclophilin D-(CypD)-dependent necrosis and a recently described additional form of regulated cell death called ferroptosis, are dependent on iron or iron-dependent reactive oxygen species (ROS). However, whether the accumulation of intracellular iron itself induces ferroptosis or other forms of cell death is largely elusive. In present study, we study the role of intracellular iron overload itself-induced cell death mechanisms by using ferric ammonium citrate (FAC) and a membrane-permeable Ferric 8-hydroxyquinoline complex (Fe-8HQ) respectively. We show that FAC-induced intracellular iron overload causes ferroptosis. We also identify 3-phosphoinositide-dependent kinase 1 (PDK1) inhibitor GSK2334470 as a potent ferroptosis inhibitor. Whereas, Fe-8HQ-induced intracellular iron overload causes unregulated necrosis, but partially activates PARP-1 dependent parthanatos. Interestingly, we identify many phenolic compounds as potent inhibitors of Fe-8HQ-induced cell death. In conclusion, intracellular iron overload-induced cell death form might be dependent on the intracellular iron accumulation rate, newly identified cell death inhibitors in our study that target ferroptosis and unregulated oxidative cell death represent potential therapeutic strategies against iron overload related diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Reduction of CO2 using a Rhenium Bipyridine Complex Containing Ancillary BODIPY Redox Reservoirs

The reduction of carbon dioxide to chemical fuels such as carbon monoxide is an important challenge in the field of renewable energy conversion. Given the thermodynamic stability of carbon dioxide, it is difficult to efficiently activate this substrate in a selective fashion and the development of new electrocatalysts for CO2 reduction is of prime importance. To this end, we have prepared and studied a new fac-ReI(CO)3 complex supported by a bipyridine ligand containing ancillary BODIPY moieties ([Re(BB2)(CO)3Cl]). Voltammetry experiments revealed that this system displays a rich redox chemistry under N2, as [Re(BB2)(CO)3Cl] can be reduced by up to four electrons at modest potentials. These redox events have been characterized as the ReI/0 couple, and three ligand based reductions two of which are localized on the BODIPY units. The ability of the BB2 ligand to serve as a noninnocent redox reservoir is manifest in an enhanced electrocatalysis with CO2 as compared to an unsubstituted Re-bipyridine complex lacking BODIPY units ([Re(bpy)(CO)3Cl]). The second order rate constant for reduction of CO2 by [Re(BB2)(CO)3Cl] was measured to be k = 3400 M 1s 1 at an applied potential of 2.0 V versus SCE, which is roughly three times greater than the corresponding unsubstituted Re-bipyridine homologue. Photophysical and photochemical studies were also carried out to determine if [Re(BB2)(CO)3Cl] was a competent platform for CO2 reduction using visible light. These experiments showed that this complex supports unusual excited state dynamics that are not typically observed for fac- ReI(CO)3 complexes.

Teesdale, Justin↗
DOE OSTI2024

Pathways to formulate lightweight and ultra-lightweight 3D printable cementitious composites

Here, this paper studies the pathways to formulate lightweight and ultra-lightweight 3D printable cementitious composites. A hybrid approach was proposed by combining the advantages of traditional chemical-induced foaming (foaming approach) and lightweight particulate inclusions (synthetic foam approach). A comprehensive experimental program was conducted to evaluate the effects of foaming agents and fly ash cenosphere (FAC) on the printability, microstructure, mechanical and thermal properties of 3D printed samples. The results showed that the hybrid approach could produce a mixture with a density as low as 470 kg/m 3 while ensuring good flowability and buildability owing to the lubricating effect of foaming and supporting skeleton formed by FAC. In addition, a three-step homogenization procedure was also developed to predict the effective elastic modulus and thermal conductivity of 3D printable cementitious composites and cementitious foam. The findings of the study highlighted the effectiveness of the hybrid approach in formulating 3D printable ultra-lightweight cementitious composites in thermal insulation and acoustic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Stereoelectronic Effects in Cl 2 Elimination from Binuclear Pt(III) Complexes

Halogen photoelimination is the critical energy-storing step of metal-catalyzed HX-splitting photocycles. Homo- and heterobimetallic Pt(III) complexes display among the highest quantum efficiencies for halogen elimination reactions. Herein, we examine in detail the mechanism and energetics of halogen elimination from a family of binuclear Pt(III) complexes featuring meridionally coordinated Pt(III) trichlorides. Transient absorption spectroscopy, steady-state photocrystallography, and far-infrared vibrational spectroscopy suggest a halogen elimination mechanism that proceeds via two sequential halogen-atom-extrusion steps. Solution-phase calorimetry experiments of the meridional complexes have defined the thermodynamics of halogen elimination, which show a decrease in the photoelimination quantum efficiency with an increase in the thermochemically defined Pt–X bond strength. Conversely, when compared to an isomeric facial Pt(III) trichloride, a much more efficient photoelimination is observed for the fac isomer than would be predicted based on thermochemistry. Here, this difference in the fac vs mer isomer photochemistry highlights the importance of stereochemistry on halogen elimination efficiency and points to a mechanism-based strategy for achieving halogen elimination reactions that are both efficient and energy storing.

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

Mechanistic Insights into CO 2 -to-CO Photoreduction by Proton-Responsive Imidazole–Pyridine Re(I) Complexes

Two Re(I) tricarbonyl complexes with imidazole-pyridine ligands, fac- [Re(CO) 3 (pbiH)Cl], (Re-pbiH), and fac-[Re(CO) 3 (bbzp)Cl] (Re-bbzp), where pbiH= 2-(2-pyridy)benzimidazole, bbzp = 2,6-bis(2-benzimidazolyl)pyridine, were synthesized, and their photophysical, electrochemical, and photochemical properties were investigated for application as photocatalysts for CO 2 -to-CO reduction. Upon light irradiation (λ > 370 nm) in CO 2 -saturated CH3CN using 1,3-dimethyl-2-phenyl-2,3-dihydro-1Hbenzo[ d]imidazole (BIH) as a sacrificial donor, Re-bbzp promotes CO formation with a turnover number (TON CO ) of 45 ± 2, whereas Re-pbiH displayed a significantly lower activity (TON CO = 8 ± 1). The role of the bbzp ligand in the photocatalytic behavior was examined in detail using IR spectroelectrochemistry (IR-SEC) together with in situ FTIR and UV−vis spectroscopy under photocatalytic conditions, revealing the formation of key intermediates involved in CO 2 activation. The superior activity of Re-bbzp was rationalized by its ability to function as a proton relay and two-electron acceptor. The role as a proton relay was further supported by the observation of a kinetic isotope effect (KIE = 1.5) when the deuterated electron donor BID was employed, in agreement with the unusual decrease in catalytic activity observed upon addition of Brønsted bases. Overall, these results provide new insights into the role of ligand-based proton-responsive sites in Re(I) tricarbonyl complexes and their impact on CO 2 reduction photocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Nanoscale Photoexcited Carrier Dynamics in Perovskites

The optoelectronic properties of lead halide perovskite thin films can be tuned through compositional variations and strain, but the associated nanocrystalline structure makes it difficult to untangle the link between composition, processing conditions, and ultimately material properties and degradation. Here, we study the effect of processing conditions and degradation on the local photoconductivity dynamics in [(CsPbI 3 ) 0.05 (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 ] and (FA 0.7 Cs 0.3 PbI 3 ) perovskite thin films using temporally and spectrally resolved microwave near-field microscopy with a temporal resolution as high as 5 ns and a spatial resolution better than 50 nm. For the latter FACs formulation, we find a clear effect of the process annealing temperature on film morphology, stability, and spatial photoconductivity distribution. After exposure of samples to ambient conditions and illumination, we find spectral evidence of halide segregation-induced degradation below the instrument resolution limit for the mixed halide formulation, while we find a clear spatially inhomogeneous increase in the carrier lifetime for the FACs formulation annealed at 180 degrees C.

14 SOLAR ENERGY↗
DOE OSTI2019

[(MeCN) 3 Co(C 2 F 5 ) 3 ]: A Versatile Precursor to Cobalt(III) Perfluoroethyl Complexes

The air-stable [fac-(MeCN) 3 Co(C 2 F 5 ) 3 ] (1) was prepared through the reaction of cobalt(II) bromide with [Me 3 Si-C 2 F 5 ] and AgF. Upon reaction of 1 with wet pyridine, the unexpected product [fac-(H 2 O) 3 Co(C 2 F 5 ) 3 ·6 pyridine] (2) was formed in which water coordinates to cobalt instead of pyridine, and the pyridines form short contacts with each of the hydrogen atoms in the bound water molecules. Facile exchange of the bound acetonitrile ligands in 1 with terpyridine (tpy) and bipyridine (bpy) did occur, however, affording [(tpy)Co(C 2 F 5 ) 3 ] (5) and [(bpy)Co(C 2 F 5 ) 3 (MeCN)] (6) in high yields.

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

Enhanced Electrocatalytic and Selective CO 2 -to-CO Reduction by a Rhenium(I) Complex Bearing 6,6′-Substituted 2,2′-Bipyridines

The electrochemical reduction of CO 2 (CO 2 RR) into value-added chemicals offers a promising route toward a circular carbon economy and reduced reliance on fossil fuels. A detailed understanding of the structural and electronic factors governing the performance of molecular CO 2 RR electrocatalysts is essential for the design of efficient, tunable systems. Here, in this study, we report a series of rhenium(I) complexes, fac-[Re I (6,6′-(R) 2 -bpy)(CO) 3 Cl] (bpy = 2,2′-bipyridine; R = mesityl (mes), 2,4,6-triisopropylphenyl (trip), or isophthalic acid (phth)) and evaluate their electrocatalytic activity. Among these, fac-[Re I (6,6′-(mes) 2 -bpy)(CO) 3 Cl] exhibited the highest performance, enabling selective CO 2 -to-CO conversion for 1 hour with Faradaic efficiency (FE) > 97%, representing an unprecedented activity level for a Re-bpy catalysts. Single-crystal X-ray diffraction and density functional theory (DFT) calculations indicated that favorable CO 2 binding could be promoted by the tilting of the 6,6′-(mes)2-bpy ligand (from the Re-CO coordination plane), providing mechanistic insight into the observed enhancement. The study consequently demonstrates a rational correlation between the CO 2 electrocatalytic performance of Re-bpy catalysts and their structural variations, as derived from X-ray data and corroborated by computational modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Photocatalytic Conversion of CO2 to CO using Rhenium Bipyridine Platforms Containing Ancillary Phenyl or BODIPY Moieties

Harnessing of solar energy to drive the reduction of carbon dioxide to fuels requires the development of efficient catalysts that absorb sunlight. In this work, we detail the synthesis, electrochemistry and photophysical properties of a set of homologous fac-ReI(CO)3 complexes containing either an ancillary phenyl (8) or BODIPY (12) substituent. These studies demonstrate that both the electronic properties of the rhenium center and BODIPY chromophore are maintained for these systems. Photolysis studies demonstrate that both assemblies 8 and 12 are competent catalysts for the photochemical reduction of CO2 to CO in DMF using triethanolamine (TEOA) as a sacrificial reductant. Both these systems display TOFs for photocatalytic CO production upon irradiation with light ( ex 400 nm) of ~5 hr 1 with TON values of approximately 20. Although structural and photophysical measurements demonstrate that electronic coupling between the BODIPY and fac-ReI(CO)3 units is limited for complex 12, this work clearly shows that the photoactive BODIPY moiety is tolerated during catalysis and does not interfere with the observed photochemistry. When taken together, these results provide a clear roadmap for the development of advanced rhenium bipyridine complexes bearing ancillary BODIPY groups for the efficient photocatalytic reduction of CO2 using visible light.

Andrade, Gabriel↗
DOE OSTI2016

Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction

Condensation of fac -Re(5,6-diamino-1,10-phenanthroline)(CO) 3 Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO 2 reduction to CO in acetonitrile electrolyte. X-ray photoelectron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm –2 with 96 ± 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac -Re(1,10-phenanthroline)(CO) 3 Cl, and turnover numbers greater than 12,000. In contrast to the molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. Here, this work establishes graphite-conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗