Bryan Eichhorn

[(ZnSb6)2]4−: a new structure type for coupled norbornadiene-like subunits

Co-reporter:Yi Wang;Peter Zavalij

Chemical Communications 2017 vol. 53(Issue 84) pp:11600-11602

Publication Date(Web):2017/10/19

DOI:10.1039/C7CC07454A

The norbornadiene-like bimetallic dimer [(ZnSb6)2]4− anion (1) was prepared by direct extraction from a ternary alloy with nominal composition “K6ZnSb5” in ethylenediamine/toluene/2,2,2-crypt solutions. The structure represents a new type for coupled norbornadiene subunits, however, distortions around the Zn2+ ions degrade the overall symmetry. The Zn2+ ions achieve a 16e− configuration and reside in near perfect ZnSb3 triangular coordination environments. DFT calculations reveal a 2.35 eV HOMO–LUMO gap and suggest covalent bonding between the Zn and Sb atoms.

Sb@Ni12@Sb20–/+ and Sb@Pd12@Sb20n Cluster Anions, Where n = +1, −1, −3, −4: Multi-Oxidation-State Clusters of Interpenetrating Platonic Solids

Co-reporter:Yi WangMelanie Moses-DeBusk, Lauren StevensJunkai Hu, Peter Zavalij, Kit BowenBrett I. Dunlap, Evan R. Glaser, Bryan Eichhorn

Journal of the American Chemical Society 2016 Volume 139(Issue 2) pp:619-622

Publication Date(Web):December 24, 2016

DOI:10.1021/jacs.6b12109

K5Sb4 and K3Sb7 Zintl ion precursors react with Pd(PPh3)4 in ethylenediamine/toluene/PBu4+ solutions to give crystals of Sb@Pd12@Sb20n–/PBu4+ salts, where n = 3, 4. The clusters are structurally identical in the two charge states, with nearly perfect Ih point symmetry, and can be viewed as an Sb@Pd12 icosahedron centered inside of an Sb20 dodecahedron. The metric parameters suggest very weak Sb–Sb and Pd–Pd interactions with strong radial Sb–Pd bonds between the Sb20 and Pd12 shells. All-electron DFT analysis shows the 3– ion to be diamagnetic with Ih symmetry and a 1.33 eV HOMO–LUMO gap, whereas the 4– ion undergoes a Jahn–Teller distortion to an S = 1/2 D3d structure with a small 0.1 eV gap. The distortion is predicted to be small and is not discernible by crystallography. Laser desorption–ionization time-of-flight mass spectrometry (LDI-TOF MS) studies of the crystalline samples show intense parent Sb@Pd12@Sb20– ions (negative ion mode) and Sb@Pd12@Sb20+ (positive ion mode) along with series of Sb@Pd12-y@Sb20-x–/+ ions. Ni(cyclooctadiene)2 reacts with K3Sb7 in en/tol/Bu4PBr solvent mixtures to give black precipitates of Sb@Ni12@Sb20n– salts that give similar Sb@Ni12@Sb20–/+ parent ions and Sb@Ni12-y@Sb20-x–/+ degradation series in the respective LDI-TOF MS studies. The solid-state and gas-phase studies of the icosahedral Sb@M12@Sb20n–/n+ ions show that the clusters can exist in the −4, −3, −1, +1 (M = Pd) and +1, −1 (M = Ni) oxidation states. These multiple-charge-state clusters are reminiscent of redox-active fullerenes (e.g., C60n, where n = +1, 0, −1, −2, −3, −4, −5, −6).

Elucidation of the Fe(III) Gallate Structure in Historical Iron Gall Ink

Co-reporter:Aldo Ponce, Lynn B. Brostoff, Sarah K. Gibbons, Peter Zavalij, Carol Viragh, Joseph Hooper, Sufian Alnemrat, Karen J. Gaskell, and Bryan Eichhorn

Analytical Chemistry 2016 Volume 88(Issue 10) pp:5152

Publication Date(Web):April 8, 2016

DOI:10.1021/acs.analchem.6b00088

Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate·xH2O (x = ∼1.5–3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for Fe(III) gallate has been commonly cited.

Synthesis, Structure, and Properties of Al(Rbpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds

Co-reporter:Samantha DeCarlo, Dennis H. Mayo, Warren Tomlinson, Junkai Hu, Joseph Hooper, Peter Zavalij, Kit Bowen, Hansgeorg Schnöckel, and Bryan Eichhorn

Inorganic Chemistry 2016 Volume 55(Issue 9) pp:4344-4353

Publication Date(Web):April 11, 2016

DOI:10.1021/acs.inorgchem.6b00034

The neutral homoleptic tris-bpy aluminum complexes Al(Rbpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral Rbpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al3+ metal centers coordinated by three bipyridine (bpy•)1– monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral Rbpy or Rbpy2– dianions, respectively. Magnetic susceptibility measurements (4–300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the Rbpy ligands to give S = 1/2 ground states with low lying S = 3/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

Synthesis of PtSn4 and Ir3Sn7 intermetallic nanoparticles from bimetallic Zintl cluster precursors

Co-reporter:Domonique O. Downing, Zhufang Liu, Bryan W. Eichhorn

Polyhedron 2016 Volume 103(Part A) pp:66-70

Publication Date(Web):8 January 2016

DOI:10.1016/j.poly.2015.09.033

Controlled I2 oxidations of preformed Zintl clusters [Pt2Sn9(PPh3)]2− and [Sn9Ir(cod)]3−, give well ordered tin-rich intermetallic nanoparticles (NPs) of PtSn4 and Ir3Sn7, respectively. The intermetallics were characterized by HR-TEM and XRD analysis. Both clusters have strong structural similarities with the final intermetallic, which appears to be an important factor in determining the phase of the resulting intermetallic NP. Despite the 1:9 (Ir:Sn) atomic ratio of the [Sn9Ir(cod)]3− cluster, ordered Ir3Sn7 NPs were formed instead of the compositionally-similar IrSn4 phases. PtSn4 is difficult to prepare and isolate due to the formation of other known Pt–Sn phases, such as PtSn, PtSn2 and Pt3Sn.Intermetallic nanoparticles of PtSn4 and Ir3Sn7 can be prepared directly from the intermetallic Zintl cluster anions [Pt2Sn9(PPh3)]2− and [Sn9Ir(cod)]3−, respectively. The close structural similarities between the clusters and intermetallic phases facilitate the low temperature transformations.

Confined Sulfur in Microporous Carbon Renders Superior Cycling Stability in Li/S Batteries

Co-reporter:Yunhua Xu;Yang Wen;Yujie Zhu;Karen Gaskell;Katie A. Cychosz;Kang Xu;Chunsheng Wang

Advanced Functional Materials 2015 Volume 25( Issue 27) pp:4312-4320

Publication Date(Web):

DOI:10.1002/adfm.201500983

The use of sulfur in the next generation Li-ion batteries is currently precluded by its poor cycling stability caused by irreversible Li₂S formation and the dissolution of soluble polysulfides in organic electrolytes that leads to parasitic cell reactions. Here, a new C/S cathode material comprising short-chain sulfur species (predominately S₂) confined in carbonaceous subnanometer and the unique charge mechanism for the subnano-entrapped S₂ cathodes are reported. The first charge–discharge cycle of the C/S cathode in the carbonate electrolyte forms a new type of thiocarbonate-like solid electrolyte interphase (SEI). The SEI coated C/S cathode stably delivers ≈600 mAh g⁻¹ capacity over 4020 cycles (0.0014% loss cycle⁻¹) at ≈100% Coulombic efficiency. Extensive X-ray photoelectron spectroscopy analysis of the discharged cathodes shows a new type of S₂ species and a new carbide-like species simultaneously, and both peaks disappear upon charging. These data suggest a new sulfur redox mechanism involving a separated Li⁺/S²⁻ ion couple that precludes Li₂S compound formation and prevents the dissolution of soluble sulfur anions. This new charge/discharge process leads to remarkable cycling stability and reversibility.

Kinetically Stabilized Pd@Pt Core–Shell Octahedral Nanoparticles with Thin Pt Layers for Enhanced Catalytic Hydrogenation Performance

Co-reporter:Peipei Zhang, Yibo Hu, Baihai Li, Qiuju Zhang, Chen Zhou, Hongbo Yu, Xuejun Zhang, Liang Chen, Bryan Eichhorn, and Shenghu Zhou

ACS Catalysis 2015 Volume 5(Issue 2) pp:1335

Publication Date(Web):January 16, 2015

DOI:10.1021/cs501612g

This study investigates the structural stability of small Pd@Pt core@shell octahedral nanoparticles (NPs) and their shell thickness dependent catalytic performance for p-chloronitrobenzene hydrogenation with H2. The 6–8 nm Pd@Pt octahedral NPs are prepared by a sequential reduction method, and the characterization results confirm that Pd@Pt octahedral NPs with one to four atomic Pt layers can be controllably synthesized. The Pd@Pt octahedral NPs with one atomic Pt layer demonstrate excellent structural stability with the maintenance of core–shell structures as well as high catalytic stability during cycle to cycle catalytic p-chloronitrobenzene hydrogenation reactions. The alumina-supported Pd@Pt octahedral NPs illustrate a superior catalytic performance relative to individual Pt and Pd and their physical mixtures. Theoretical calculations by density functional theory suggest that the unexpected structural stability for Pd@Pt octahedral NPs with thin Pt shells and their corresponding catalytic stability during hydrogenation reactions can be ascribed to the strong binding between Pt surfaces and reactants/products in catalytic reactions. The enhanced catalytic performance of Pd@Pt octahedral NPs possibly originates from the core–shell interaction, which adjusts the electronic state of surface Pt atoms to be suitable for selective p-chloronitrobenzene hydrogenation.Keywords: core−shell; hydrogenation; nanocatalysis; p-chloronitrobenzene; Pd@Pt

Synthesis, structure, and properties of a dialumane supported by pyrazolate ligands

Co-reporter:Christopher J. Snyder, Peter Zavalij, Kit Bowen, Hansgeorg Schnöckel and Bryan Eichhorn

Dalton Transactions 2015 vol. 44(Issue 7) pp:2956-2958

Publication Date(Web):11 Dec 2014

DOI:10.1039/C4DT03533J

The dialumane [Al2][Na(Ph2pz)3]2 (1) has been prepared by the reaction of Na(Ph2pz) with a metastable solution of AlCl. The structure of 1 contains two hydrotris(pyrazolyl)borate-like Na(Ph2pz)32− moieties that are coordinated to each Al atom of the dialumane in a κ2,κ1-N,N,N fashion and several π-stacking interactions are present between the pyrazolate and phenyl rings. In solution the pyrazolate ligands in 1 are in dynamic exchange, even at −80 °C, which shows the lability of these ligands to the low-valent aluminum centers.

CO tolerance of Pt and PtSn intermetallic electrocatalysts on synthetically modified reduced graphene oxide supports

Co-reporter:Christopher M. Sims, Audaldo A. Ponce, Karen J. Gaskell and Bryan W. Eichhorn

Dalton Transactions 2015 vol. 44(Issue 3) pp:977-987

Publication Date(Web):2014/11/04

DOI:10.1039/C4DT02544J

Pt and PtSn intermetallic nanoparticle (NP) catalysts were grown directly on various reduced graphene oxide (rGO) supports and were characterized by a combination of X-ray photoelectron spectroscopic (XPS), Raman microscopy, transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) studies. Electrochemical CO stripping and rotating disk electrochemical (RDE) experiments showed the four rGO-PtSn catalysts to be superior to the four rGO-Pt catalysts for CO and CO–H2 electrooxidation in acidic solutions regardless of the rGO support, in agreement with earlier reports on PtSn NP electrocatalysts. For the four rGO-Pt catalysts, the rGO support causes a 70 mV spread in CO oxidation peak potential (ΔEpeak) and a 200 mV spread in CO–H2 electrooxidation onset. The more oxygenated graphenes show the lowest CO oxidation potentials and the best CO tolerance. For the four rGO-PtSn intermetallic catalysts, a ∼160 mV spread in CO–H2 electrooxidation onset is observed. With the exception of the nitrogen-doped graphene (NGO), a similar trend in enhanced CO electrooxidation properties with increasing oxygen content in the rGO support is observed. The NGO-PtSn electrocatalyst was superior to the other rGO-PtSn catalysts and showed the largest improvement in CO tolerance relative to the pure Pt system. The origin of this enhancement appears to stem from the unique rGO-PtSn support interaction in this system. These results are discussed in the context of recent theoretical and experimental studies in the literature.

CO2 activation and carbonate intermediates: an operando AP-XPS study of CO2 electrolysis reactions on solid oxide electrochemical cells

Co-reporter:Yi Yu, Baohua Mao, Aaron Geller, Rui Chang, Karen Gaskell, Zhi Liu and Bryan W. Eichhorn

Physical Chemistry Chemical Physics 2014 vol. 16(Issue 23) pp:11633-11639

Publication Date(Web):28 Apr 2014

DOI:10.1039/C4CP01054J

Through the use of ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, carbon dioxide (CO2) electrolysis reactions (CO2 + 2e− → CO + O2−) and carbon monoxide (CO) electro-oxidation reactions (CO + O2− → CO2 + 2e−) over cerium oxide electrodes have been investigated in the presence of 0.5 Torr CO–CO2 gas mixtures at ∼600 °C. Carbonate species (CO32−) are identified on the ceria surface as reaction intermediates. When CO2 electrolysis is promoted on ceria electrodes at +2.0 V applied bias, we observe a higher concentration of CO32− over a 400 μm-wide active region on the ceria surface, accompanied by Ce3+/Ce4+ redox changes. This increase in the CO32− steady-state concentration suggests that the process of pre-coordination of CO2 to the ceria surface to form a CO32− intermediate (CO2(g) + O2−(surface) → CO32−(surface)) precedes a rate-limiting electron transfer process involving CO32− reduction to give CO and oxide ions (CO32−(surface) + 2Ce3+ → CO(g) + 2O2−(surface) + 2Ce4+). When the applied bias is switched to −1.5 V to promote CO electro-oxidation on ceria, the surface CO32− concentration slightly decreases from the equilibrium value, suggesting that the electron transfer process is also a rate-limiting process in the reverse direction.

Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells

Co-reporter:Chunjuan Zhang ; Yi Yu ; Michael E. Grass ; Catherine Dejoie ; Wuchen Ding ; Karen Gaskell ; Naila Jabeen ; Young Pyo Hong ; Andrey Shavorskiy ; Hendrik Bluhm ; Wei-Xue Li ; Gregory S. Jackson ; Zahid Hussain ; Zhi Liu ;Bryan W. Eichhorn

Journal of the American Chemical Society 2013 Volume 135(Issue 31) pp:11572-11579

Publication Date(Web):July 3, 2013

DOI:10.1021/ja402604u

Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H2O + 2e– → H2 + O2–) and electro-oxidation of hydrogen (H2 + O2– → H2O + 2e–) at ∼700 °C in 0.5 Torr of H2/H2O on ceria (CeO2–x) electrodes. The experiments reveal a transient build-up of surface intermediates (OH– and Ce3+) and show the separation of charge at the gas–solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH– and incorporated O2– differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH– and O2– shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H2O + Ce3+ ⇔ Ce4+ + OH– + H•) is rate limiting in both the forward (water electrolysis) and reverse (H2 electro-oxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas–solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH–/O2– potential separation resides in the reduced polarization of the Ce–OH bond due to the increase of Ce3+ on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions.

Surprising Acid/Base and Ion-Sequestration Chemistry of Sn94–: HSn93–, Ni@HSn93–, and the Sn93– Ion Revisited

Co-reporter:F. Sanem Kocak ; Domonique O. Downing ; Peter Zavalij ; Yiu-Fai Lam ; Andrei N. Vedernikov

Journal of the American Chemical Society 2012 Volume 134(Issue 23) pp:9733-9740

Publication Date(Web):April 29, 2012

DOI:10.1021/ja3018797

K4Sn9 dissolves in ethylenediamine (en) to give equilibrium mixtures of the diamagnetic HSn93– ion along with KxSn9(4–x)– ion pairs, where x = 0, 1, 2, 3. The HSn93– cluster is formed from the deprotonation of the en solvent and is the conjugate acid of Sn94–. DFT studies show that the structure is quite similar to the known isoelectronic RSn93– ions (e.g., R = i-Pr). The hydrogen atom of HSn93– (δ = 6.18 ppm) rapidly migrates among all nine Sn atoms in an intramolecular fashion; the Sn9 core is also highly dynamic on the NMR time scale. The HSn93– cluster reacts with Ni(cod)2 to give the Ni@HSn93– ion containing a hydridic hydrogen (δ = −28.3 ppm) that also scrambles across the Sn9 cluster. The Sn94– ion competes effectively with 2,2,2-crypt for binding K+ in en solutions, and the pKa of HSn93– is similar to that of en (i.e., Sn94– is a very strong Brønsted base with a pKb comparable to that of the NH2CH2CH2NH– anion). Competition studies show that the HSn93– ⇄ Sn94– + H+ equilibrium is fully reversible. The HSn93– anion is present in significant concentrations in en solutions containing 2,2,2-crypt, yet it has gone undetected for over 30 years.

Multielement Activity Mapping and Potential Mapping in Solid Oxide Electrochemical Cells through the use of operando XPS

Co-reporter:Chunjuan Zhang, Michael E. Grass, Yi Yu, Karen J. Gaskell, Steven C. DeCaluwe, Rui Chang, Gregory S. Jackson, Zahid Hussain, Hendrik Bluhm, Bryan W. Eichhorn, and Zhi Liu

ACS Catalysis 2012 Volume 2(Issue 11) pp:2297

Publication Date(Web):September 21, 2012

DOI:10.1021/cs3004243

Spatially resolved ambient pressure X-ray photoelectron spectroscopy has been used to measure and visualize regions of electrochemical activity, local surface potential losses, overpotentials, and oxidation state changes on single sided ceria/yttria-stabilized zirconia (YSZ)/Pt solid oxide electrochemical cells. When hydrogen electro-oxidation (negative applied bias) or water electrolysis (positive applied bias) is promoted on the ceria electrocatalyst, the Ce3+/Ce4+ ratios shift away from equilibrium values and thereby demarcate electrochemically active regions on the ceria electrode. In addition to the ceria oxidation state shifts, inactive surface impurities with high photoelectron cross sections, such as Si, can provide local markers of activity through chemical and surface potential mappings under various electrochemical conditions. Localized removal of chemically active carbonaceous surface impurities also reveals regions of electrochemical oxidation activity on the ceria electrode. Finally, we show that electrochemical polarization of solid oxide electrochemical cells under different gas environments is used to control the ceria surface chemical state and oxygen vacancy density.Keywords: ambient pressure XPS; ceria; operando; solid oxide electrochemical cell

CO tolerance of nano-architectured Pt–Mo anode electrocatalysts for PEM fuel cells

Co-reporter:Jenny E. Hu, Zhufang Liu, Bryan W. Eichhorn, Gregory S. Jackson

International Journal of Hydrogen Energy 2012 Volume 37(Issue 15) pp:11268-11275

Publication Date(Web):August 2012

DOI:10.1016/j.ijhydene.2012.04.094

PEM fuel cell membrane electrode assemblies with Nafion electrolytes and commercial Pt-based cathodes were tested with Pt0.8Mo0.2 alloy and MoOx@Pt core–shell anode electrocatalysts for CO tolerance and short-term stability to corroborate earlier thin-film RDE results. Polarization curves at 70 °C for the Pt0.8Mo0.2 alloy in H2 with 25–1000 ppm CO showed a significant increase in CO tolerance based on peak power densities in comparison to PtRu electrocatalysts. MoOx@Pt core–shell electrocatalysts, which showed extremely high activity for H2 in 1000 ppm CO during RDE studies, performed relatively poorly in comparison to the Pt0.8Mo0.2 and PtRu alloys for the same total catalyst loading on a per area basis in MEA testing. The discrepancy is attributed to residual stabilizer from the core–shell synthesis impacting catalyst-ionomer interfaces. Nonetheless, the MoOx@Pt electrochemical performance is superior on a per-gram-of-precious-metal basis to the Pt0.8Mo0.2 electrocatalyst for CO concentrations below 100 ppm. Due to cross-membrane Mo migration, the stability of the Mo-containing anode electrocatalysts remains a challenge for developing stable enhanced CO tolerance for low-temperature PEM fuel cells.Highlights► Pt0.8Mo0.2 electrocatalysts show reduced anode overpotentials due to CO poisioning. ► We demonstrate enhanced CO tolerance per g of precious metal for MoOx@Pt core–shell catalysts. ► Pt0.8Mo0.2 alloy electrocatalysts show improved stability over MoOx@Pt core–shell catalysts.

Tuning the CO-tolerance of Pt-Fe bimetallic nanoparticle electrocatalysts through architectural control

Co-reporter:Zhufang Liu, Gregory S. Jackson and Bryan W. Eichhorn

Energy & Environmental Science 2011 vol. 4(Issue 5) pp:1900-1903

Publication Date(Web):14 Apr 2011

DOI:10.1039/C1EE01125A

We report a new and simple method for creating Pt-Fe bimetallic nanoparticle (NP) electrocatalysts with various architectures (random alloy, intermetallic and core-shell) and their architecture-dependent electrocatalytic activity for CO/H2oxidation.

Dynamic properties of the fluxional Rh2H(μ-PPh2)2(PPh3)3−1 complex

Co-reporter:Domonique O. Downing, Peter Zavalij, Bryan W. Eichhorn

Inorganica Chimica Acta 2011 Volume 375(Issue 1) pp:329-332

Publication Date(Web):1 September 2011

DOI:10.1016/j.ica.2011.05.028

The rhodium dimer [Rh2H(PPh2)2(PPh3)3]− was prepared from RhCl(PPh3)3 and K4Sn9 in the presence of 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-crypt)]+ salt was isolated and characterized via NMR and X-ray diffraction studies. The solid state structure reveals a binuclear, diphenylphosphido-bridged, 32 electron Rh(I)–Rh(I) complex with edge-shared tetrahedral and square planar Rh centers with overall Cs point symmetry. 1-D and 2-D 1H, 31P, and 31P{1H} NMR experiments were used to characterize the complex.Graphical abstractThe dirhodium Rh2H(μ-PPh2)2(PPh3)3−1 complex was synthesized by reducing Wilkinson’s catalyst in the presence of K4Sn9 and 2,2,2-cryptand. The 32-electron phosphido-bridged structure has Cs point symmetry and is dynamic in solution. The complex was characterized by X-ray crystallography along with 1-D and 2-D 1H and 31P NMR spectroscopy.Highlights► Diphenylphosphido-bridged dirhodium, 32 electron Rh2 complex synthesized. ► Asymmetric rhodium centers with pseudo-tetrahedral and square planar Rh centers. ► 1H and 31P NMR experiments reveal the highly dynamic structure in solution.

Reactions of exo-Substituted RSn93 Clusters with Pd: Endohedral Cluster Formation and Oxidative Insertion

Co-reporter:F. Sanem Kocak;Peter Zavalij

Chemistry - A European Journal 2011 Volume 17( Issue 17) pp:4858-4863

Publication Date(Web):

DOI:10.1002/chem.201002019

Abstract

Pyridine/ethylenediamine solutions of [Sn₉SnCy₃]³⁻ (1) react with [Pd(PPh₃)₄] to give new clusters [Pd@Sn₉SnCy₃]³⁻ (2) and [Pd@Sn₉PdSnCy₃]³⁻ (3), depending on stoichiometry. These compounds are formed sequentially and are the first transition metal derivates of exo-substituted Zintl clusters. Oxidative insertion of a Pd atom into the Pd@Sn₉SnCy₃ bond of 2 to form 3 represents a new reaction type for Zintl cluster compounds. The conversion Sn₉⁴⁻123 is a rare case in which charge and mass are conserved in a series of Zintl clusters. Complexes 1, 2, and 3 are all highly fluxional in solution. In all three clusters, the nine Sn vertices are in rapid exchange on the NMR timescale. In 1 and 2, the exo-SnCy₃ substituent also scrambles intramolecularly around the outside of the clusters. In 3, the SnCy₃ group remains attached to the vertex Pd atom. The disparate reactions with the other RSn₉³⁻ ions are discussed.

Photoelectron spectroscopic and computational studies of the and anions

Co-reporter:Andrej Grubisic;F. Sanem Kocak;Haopeng Wang;Yeon-Jae Ko;Mark R. Pederson;Xiang Li;Bryan W. Eichhorn;Kit H. Bowen

PNAS 2011 Volume 108 (Issue 36 ) pp:

Publication Date(Web):2011-09-06

DOI:10.1073/pnas.1105052108

A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, and were prepared from “preassembled” clusters generated from crystalline samples of [K(2,2,2-crypt)]2[Pt @ Pb12] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)]2[Pt @ Pb12] also provided access to K[Pt @ Pbn]- anions in the gas phase (i.e., the K+ salts of the anions). Anion photoelectron spectra of , , and K[Pt @ Pb12]1- are presented. Extensive density functional theory calculations on and provided candidate structures and anion photoelectron spectra for and . Together, the calculated and measured photoelectron spectra show that and endohedral complexes maintain their respective D4d and slightly distorted Ih symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase.

Preferential CO Oxidation in Hydrogen: Reactivity of Core−Shell Nanoparticles

Co-reporter:Anand Udaykumar Nilekar ; Selim Alayoglu ; Bryan Eichhorn ;Manos Mavrikakis

Journal of the American Chemical Society 2010 Volume 132(Issue 21) pp:7418-7428

Publication Date(Web):May 11, 2010

DOI:10.1021/ja101108w

We report on the first-principles-guided design, synthesis, and characterization of core−shell nanoparticle (NP) catalysts made of a transition metal core (M = Ru, Rh, Ir, Pd, or Au) covered with a ∼1−2 monolayer thick shell of Pt atoms (i.e., a M@Pt core−shell NP). An array of experimental techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, and temperature-programmed reaction, are employed to establish the composition of the synthesized NPs. Subsequent studies of these NPs’ catalytic properties for preferential CO oxidation in hydrogen-rich environments (PROX), combined with Density Functional Theory (DFT)-based mechanistic studies, elucidate important trends and provide fundamental understanding of the reactivity of Pt shells as a function of the core metal. Both the PROX activity and selectivity of several of these M@Pt core−shell NPs are significantly improved compared to monometallic and bulk nonsegregated bimetallic nanoalloys. Among the systems studied, Ru@Pt core−shell NPs exhibit the highest PROX activity, where the CO oxidation is complete by 30 °C (1000 ppm CO in H2). Therefore, despite their reduced Pt content, M@Pt core−shell NPs afford the design of more active PROX catalysts. DFT studies suggest that the relative differences in the catalytic activities for the various core−shell NPs originate from a combination of (i) the relative availability of CO-free Pt surface sites on the M@Pt NPs, which are necessary for O2 activation, and (ii) a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.

Heterogeneous films of ordered CeO2/Ni concentric nanostructures for fuel cell applications

Co-reporter:Chunjuan Zhang, Jessica Grandner, Ran Liu, Sang Bok Lee and Bryan W. Eichhorn

Physical Chemistry Chemical Physics 2010 vol. 12(Issue 17) pp:4295-4300

Publication Date(Web):01 Dec 2009

DOI:10.1039/B918587A

Heterogeneous films of ordered CeO2/Ni concentric nanostructures have been fabricated through template-assisted electrodeposition. The free-standing films of Ni metal (8 μm thickness) contain ordered arrays of ceria tubes (200 nm OD, 100 nm ID). Ni/CeO2 coaxial nanotubes were also obtained by tuning experimental conditions. The interfacial contact area within the 3-dimensional oxide nanotube/nickel matrix is ∼100 times greater than 2-dimensional thin films of nickel and ceria of the same area. The use of the film as an anode electrocatalyst/current collector is demonstrated in a solid oxide fuel cell.

PtSn Intermetallic, CoreShell, and Alloy Nanoparticles as CO-Tolerant Electrocatalysts for H2 Oxidation

Co-reporter:Zhufang Liu Dr.;GregS. Jackson ;BryanW. Eichhorn

Angewandte Chemie 2010 Volume 122( Issue 18) pp:3241-3244

Publication Date(Web):

DOI:10.1002/ange.200907019

PtSn Intermetallic, CoreShell, and Alloy Nanoparticles as CO-Tolerant Electrocatalysts for H2 Oxidation

Co-reporter:Zhufang Liu Dr.;GregS. Jackson ;BryanW. Eichhorn

Angewandte Chemie International Edition 2010 Volume 49( Issue 18) pp:3173-3176

Publication Date(Web):

DOI:10.1002/anie.200907019

PtMo Alloy and MoOx@Pt Core−Shell Nanoparticles as Highly CO-Tolerant Electrocatalysts

Co-reporter:Zhufang Liu ; Jenny E. Hu ; Qi Wang ; Karen Gaskell ; Anatoly I. Frenkel ; Gregory S. Jackson

Journal of the American Chemical Society 2009 Volume 131(Issue 20) pp:6924-6925

Publication Date(Web):May 6, 2009

DOI:10.1021/ja901303d

PtMo alloy and MoOx@Pt core−shell nanoparticles (NPs) were successfully synthesized by a chemical coreduction and sequential chemical reduction method, respectively. Both the carbon-supported alloy and core−shell NPs show substantially higher CO tolerance, compared to the commercialized E-TEK PtRu alloy and Pt catalyst. These novel nanocatalysts can be potentially used as highly CO-tolerant anode electrocatalysts in proton exchange membrane fuel cells.

Substituent-dependent exchange mechanisms in highly fluxional RSn93− anions

Co-reporter:F. Sanem Kocak, Peter Y. Zavalij, Yiu-Fai Lam and Bryan W. Eichhorn

Chemical Communications 2009 (Issue 28) pp:4197-4199

Publication Date(Web):12 Jun 2009

DOI:10.1039/B905239A

119Sn NMR studies show that the RSn93− ions (R = i-Pr, Sn(C6H11)3) are highly fluxional in solution, where the exchange mechanisms involve rapid migration of the R group in the latter but not in the former.

Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt−Ru Core−Shell and Alloy Nanoparticles

Co-reporter:Selim Alayoglu, Peter Zavalij, Bryan Eichhorn, Qi Wang, Anatoly I. Frenkel and Peter Chupas

ACS Nano 2009 Volume 3(Issue 10) pp:3127

Publication Date(Web):September 4, 2009

DOI:10.1021/nn900242v

A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core−shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are crystalline homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 Å. In contrast, the 1−2 monolayer thick Pt shells are relatively crystalline but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination numbers and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-separated in the core and shell components and that the interface between the core and shell is quite normal.Keywords: catalysts; core−shell; EXAFS; nanoparticles; structure−property relationships

In Situ Phase Separation of NiAu Alloy Nanoparticles for Preparing Highly Active Au/NiO CO Oxidation Catalysts

Co-reporter:Shenghu Zhou Dr.;Hongfeng Yin Dr.;Viviane Schwartz Dr.;Zili Wu Dr.;David Mullins Dr. ;Steven H. Overbury Dr.;Sheng Dai Dr.

ChemPhysChem 2008 Volume 9( Issue 17) pp:2475-2479

Publication Date(Web):

DOI:10.1002/cphc.200800587

AuPt Alloy Nanoparticles for CO-Tolerant Hydrogen Activation: Architectural Effects in Au-Pt Bimetallic Nanocatalysts

Co-reporter:S. Zhou;G. S. Jackson;B. Eichhorn

Advanced Functional Materials 2007 Volume 17(Issue 16) pp:

Publication Date(Web):5 SEP 2007

DOI:10.1002/adfm.200700216

Colloidal suspensions of AuPt alloy nanoparticles (NPs) were prepared by using a rapid butyllithium reduction of Au³⁺ and Pt⁴⁺ precursors in oleylamine. The resulting 2.5 nm (av) particles were characterized by TEM with EDX, XRD, XPS and UV-vis spectroscopy. With less butyllithium, nanowires are formed from fused NPs and grow to 100 nm in length. The activities of three different AuPt NP architectures (alloy, contact aggregate and monometallic NPs) were evaluated for catalytic hydrogen oxidation in CO-contaminated fuel streams (1.0 % Pt loadings in Al₂O₃ supports). The alloy catalyst showed superior H₂ and CO oxidation activity, was unaffected by iron promoters and appears to operate by a different mechanism. The heteroaggregate showed a marked improvement in activity with iron promoters and is more selective for CO oxidation.

The closo-Pb102− Zintl ion in the [Ni@Pb10]2− cluster

Co-reporter:Emren N. Esenturk, James Fettinger and Bryan Eichhorn

Chemical Communications 2005 (Issue 2) pp:247-249

Publication Date(Web):25 Oct 2004

DOI:10.1039/B412082E

The cluster [Ni@Pb10]2−, prepared from Pb94− and Ni(COD)2, contains a new Zintl ion subunit, closo-Pb102−, centered by a Ni atom.

Facile pyramidal inversion at phosphorus in [R3EP7W(CO)3]2− type complexes: An EXSY NMR study

Co-reporter:Banu Kesanli, Sundeep P. Mattamana, Janet Danis, Bryan Eichhorn

Inorganica Chimica Acta 2005 Volume 358(Issue 11) pp:3145-3151

Publication Date(Web):1 July 2005

DOI:10.1016/j.ica.2005.03.008

A series of [R3EP7W(CO)3]2− complexes where (E = Si, Ge, Sn, Pb; R = alkyl, phenyl) were prepared from [P7W(CO)3]3− and R3EX reagents (X = Cl, Br) in dmf or CH3CN solutions. The Pb derivatives were prepared at −50 °C and are not thermally stable. The compounds were characterized by 31P NMR spectroscopy and selected ESI-MS studies. All compounds undergo rapid inversion at the ER3-bound phosphorus atom. The barriers to inversion were measured by way of 2D 31P EXSY experiments at various temperatures. The analysis showed very low barriers to pyramidal inversion (ΔG‡ 10.3–13.5 kcal/mol) that were essentially enthalpic in origin. The activation barriers generally increased with increasing electronegativity of the E atom and the steric bulk of the ER3 substituents. The latter was interpreted by way of a non-linear transition state.The [R3EP7W(CO)3]2− complexes where E = C, Si, Ge, Sn, Pb show inversion at P(1) with room-temperature rate constants that span more than 2 orders of magnitude. 31P EXSY NMR analysis was implemented to evaluate the kinetic parameters from the highly second-order 31P NMR spin systems.

Pt–Cu Core–Shell and Alloy Nanoparticles for Heterogeneous NOx Reduction: Anomalous Stability and Reactivity of a Core–Shell Nanostructure

Co-reporter:Shenghu Zhou;Bindhu Varughese ;Greg Jackson ;Kevin McIlwrath

Angewandte Chemie International Edition 2005 Volume 44(Issue 29) pp:

Publication Date(Web):8 JUL 2005

DOI:10.1002/anie.200500919

Cores to celebrate: At 370 °C, Pt@Cu core–shell nanoparticles rapidly alloy but the reciprocal core–shell nanoparticles, Cu@Pt (see STEM images, left: Cu spectral map; middle: Pt spectral map; right: bright-field image), are kinetically stabilized and show high activity and selectivity for NO reduction.

Pt–Cu Core–Shell and Alloy Nanoparticles for Heterogeneous NOx Reduction: Anomalous Stability and Reactivity of a Core–Shell Nanostructure

Co-reporter:Shenghu Zhou;Bindhu Varughese ;Greg Jackson ;Kevin McIlwrath

Angewandte Chemie 2005 Volume 117(Issue 29) pp:

Publication Date(Web):8 JUL 2005

DOI:10.1002/ange.200500919

Innen oder außen macht einen Unterschied: Bei 370 °C bilden Pt@Cu-Kern-Schale-Nanopartikel rasch eine Legierung, während die reziproken Kern-Schale-Nanopartikel Cu@Pt (siehe STEM-Bilder: links Cu-Spektralkarte, Mitte Pt-Spektralkarte, rechts Hellfeldbild) kinetisch stabilisiert sind und bei der NO-Reduktion hoch aktiv und selektiv wirken.

[Pt@Pb12]2−

Co-reporter:Emren N. Esenturk;James Fettinger Dr.;Yiu-Fai Lam Dr.

Angewandte Chemie 2004 Volume 116(Issue 16) pp:

Publication Date(Web):6 APR 2004

DOI:10.1002/ange.200353287

Ein platonisches Verhältnis Der abgebildete [Pb₁₂]²⁻-Icosaeder mit einem Pt-Atom im Inneren ensteht in guter Ausbeute bei der Reaktion des Zintl-Ions [Pb₉]⁴⁻ mit [Pt(PPh₃)₄]. Das I_h-symmetrische Anion ist einer von wenigen isolierten aromatischen anorganischen Clustern, die keine Kohlenstoffatome enthalten.

[Pt@Pb12]2−

Co-reporter:Emren N. Esenturk;James Fettinger Dr.;Yiu-Fai Lam Dr.

Angewandte Chemie International Edition 2004 Volume 43(Issue 16) pp:

Publication Date(Web):6 APR 2004

DOI:10.1002/anie.200353287

It's platonic: The Pt centered [Pb₁₂]²⁻ icosahedron (depicted) was prepared from the [Pb₉]⁴⁻ Zintl ion and [Pt(PPh₃)₄] in good yield. The anion has virtual I_h point symmetry and is a rare example of a free-standing carbon-free aromatic inorganic cluster.

Interpenetrating As20 Fullerene and Ni12 Icosahedra in the Onion-Skin [As@Ni12@As20]3– Ion

Co-reporter:Melanie J. Moses;James C. Fettinger;Bryan W. Eichhorn

Science 2003 Vol 300(5620) pp:778-780

Publication Date(Web):02 May 2003

DOI:10.1126/science.1082342

Abstract

The [As@Ni₁₂@As₂₀]^3– ion was prepared from As₇^3– and Ni(COD)₂ in ethylenediamine solutions and isolated as the Bu₄P⁺ salt (As, arsenic; Ni, nickel; COD, cyclooctadiene; Bu, butyl; P, phosphorus). The anion contains an icosahedral [Ni₁₂(μ₁₂-As)]^3– fragment that resides at the center of an As₂₀ dodecahedral (fullerene) cage to give an onion-skin–like [As@Ni₁₂@As₂₀]^3– cluster with I_h point symmetry. The icosahedron and pentagonal dodecahedron are reciprocal platonic solids, and the 32 surface atoms form a dimpled geodesic sphere composed of 60 triangular faces. In the gas phase, the [As@Ni₁₂@As₂₀]^3– ion sequentiallyloses all 21 As atoms to form a series of Ni₁₂As_21–_x clusters where 0 ≤ x ≤ 21, inclusively.

Heterogeneous films of ordered CeO2/Ni concentric nanostructures for fuel cell applications

Co-reporter:Chunjuan Zhang, Jessica Grandner, Ran Liu, Sang Bok Lee and Bryan W. Eichhorn

Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 17) pp:NaN4300-4300

Publication Date(Web):2009/12/01

DOI:10.1039/B918587A

Heterogeneous films of ordered CeO2/Ni concentric nanostructures have been fabricated through template-assisted electrodeposition. The free-standing films of Ni metal (8 μm thickness) contain ordered arrays of ceria tubes (200 nm OD, 100 nm ID). Ni/CeO2 coaxial nanotubes were also obtained by tuning experimental conditions. The interfacial contact area within the 3-dimensional oxide nanotube/nickel matrix is ∼100 times greater than 2-dimensional thin films of nickel and ceria of the same area. The use of the film as an anode electrocatalyst/current collector is demonstrated in a solid oxide fuel cell.

CO2 activation and carbonate intermediates: an operando AP-XPS study of CO2 electrolysis reactions on solid oxide electrochemical cells

Co-reporter:Yi Yu, Baohua Mao, Aaron Geller, Rui Chang, Karen Gaskell, Zhi Liu and Bryan W. Eichhorn

Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 23) pp:NaN11639-11639

Publication Date(Web):2014/04/28

DOI:10.1039/C4CP01054J

Through the use of ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, carbon dioxide (CO2) electrolysis reactions (CO2 + 2e− → CO + O2−) and carbon monoxide (CO) electro-oxidation reactions (CO + O2− → CO2 + 2e−) over cerium oxide electrodes have been investigated in the presence of 0.5 Torr CO–CO2 gas mixtures at ∼600 °C. Carbonate species (CO32−) are identified on the ceria surface as reaction intermediates. When CO2 electrolysis is promoted on ceria electrodes at +2.0 V applied bias, we observe a higher concentration of CO32− over a 400 μm-wide active region on the ceria surface, accompanied by Ce3+/Ce4+ redox changes. This increase in the CO32− steady-state concentration suggests that the process of pre-coordination of CO2 to the ceria surface to form a CO32− intermediate (CO2(g) + O2−(surface) → CO32−(surface)) precedes a rate-limiting electron transfer process involving CO32− reduction to give CO and oxide ions (CO32−(surface) + 2Ce3+ → CO(g) + 2O2−(surface) + 2Ce4+). When the applied bias is switched to −1.5 V to promote CO electro-oxidation on ceria, the surface CO32− concentration slightly decreases from the equilibrium value, suggesting that the electron transfer process is also a rate-limiting process in the reverse direction.

Synthesis, structure, and properties of a dialumane supported by pyrazolate ligands

Co-reporter:Christopher J. Snyder, Peter Zavalij, Kit Bowen, Hansgeorg Schnöckel and Bryan Eichhorn

Dalton Transactions 2015 - vol. 44(Issue 7) pp:NaN2958-2958

Publication Date(Web):2014/12/11

DOI:10.1039/C4DT03533J

The dialumane [Al2][Na(Ph2pz)3]2 (1) has been prepared by the reaction of Na(Ph2pz) with a metastable solution of AlCl. The structure of 1 contains two hydrotris(pyrazolyl)borate-like Na(Ph2pz)32− moieties that are coordinated to each Al atom of the dialumane in a κ2,κ1-N,N,N fashion and several π-stacking interactions are present between the pyrazolate and phenyl rings. In solution the pyrazolate ligands in 1 are in dynamic exchange, even at −80 °C, which shows the lability of these ligands to the low-valent aluminum centers.

CO tolerance of Pt and PtSn intermetallic electrocatalysts on synthetically modified reduced graphene oxide supports

Co-reporter:Christopher M. Sims, Audaldo A. Ponce, Karen J. Gaskell and Bryan W. Eichhorn

Dalton Transactions 2015 - vol. 44(Issue 3) pp:NaN987-987

Publication Date(Web):2014/11/04

DOI:10.1039/C4DT02544J

Pt and PtSn intermetallic nanoparticle (NP) catalysts were grown directly on various reduced graphene oxide (rGO) supports and were characterized by a combination of X-ray photoelectron spectroscopic (XPS), Raman microscopy, transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) studies. Electrochemical CO stripping and rotating disk electrochemical (RDE) experiments showed the four rGO-PtSn catalysts to be superior to the four rGO-Pt catalysts for CO and CO–H2 electrooxidation in acidic solutions regardless of the rGO support, in agreement with earlier reports on PtSn NP electrocatalysts. For the four rGO-Pt catalysts, the rGO support causes a 70 mV spread in CO oxidation peak potential (ΔEpeak) and a 200 mV spread in CO–H2 electrooxidation onset. The more oxygenated graphenes show the lowest CO oxidation potentials and the best CO tolerance. For the four rGO-PtSn intermetallic catalysts, a ∼160 mV spread in CO–H2 electrooxidation onset is observed. With the exception of the nitrogen-doped graphene (NGO), a similar trend in enhanced CO electrooxidation properties with increasing oxygen content in the rGO support is observed. The NGO-PtSn electrocatalyst was superior to the other rGO-PtSn catalysts and showed the largest improvement in CO tolerance relative to the pure Pt system. The origin of this enhancement appears to stem from the unique rGO-PtSn support interaction in this system. These results are discussed in the context of recent theoretical and experimental studies in the literature.

Substituent-dependent exchange mechanisms in highly fluxional RSn93− anions

Co-reporter:F. Sanem Kocak, Peter Y. Zavalij, Yiu-Fai Lam and Bryan W. Eichhorn

Chemical Communications 2009(Issue 28) pp:NaN4199-4199

Publication Date(Web):2009/06/12

DOI:10.1039/B905239A

119Sn NMR studies show that the RSn93− ions (R = i-Pr, Sn(C6H11)3) are highly fluxional in solution, where the exchange mechanisms involve rapid migration of the R group in the latter but not in the former.

TOPICS

Abstract

Abstract