Structural Evolution of Homoleptic Heterodinuclear Copper–Nickel Carbonyl Anions Revealed Using Photoelectron Velocity-Map Imaging

The homoleptic heterodinuclear copper–nickel carbonyl anions CuNi­(CO)_<i>n</i>^– (<i>n</i> = 2–4) were generated in a pulsed-laser vaporization source and investigated using photoelectron velocity-map imaging spectroscopy. The electron affinities of CuNi­(CO)₂ (2.15 ± 0.03 eV), CuNi­(CO)₃ (2.30 ± 0.03 eV), and CuNi­(CO)₄ (1.90 ± 0.04 eV) were deduced from the photoelectron spectra. Theoretical calculations at the B3LYP level were carried out to elucidate the structures and the electronic properties of CuNi­(CO)_<i>n</i>^0/1– (<i>n</i> = 1–4) and to support the experimental observations. Comprehensive comparisons between experiments and calculations suggest that there is a turnover point of the absorption site during the progressive carbonylation process. The carbonyl groups are determined to be preferentially bonded to the nickel atom. When the nickel center satisfies the 18-electron configuration, the copper atom starts to adsorb additional CO molecules. These results will shed light on the bonding mechanisms of the heterometallic carbonyl clusters

Photoelectron Velocity Map Imaging Spectroscopy of Lead Tetracarbonyl–Iron Anion PbFe(CO)₄^–

Joint research of photoelectron velocity map imaging spectroscopy and density functional theory has been performed to probe the geometrical structures and electronic properties for heterodinuclear iron–lead carbonyl cluster PbFe­(CO)₄^–, which serves as a monomer of the metal–metal bonded oligomer. The photoelectron detachment of PbFe­(CO)₄^– is recorded at two different photon energies with rich spectral features. The ground-state transition obtained at 532 nm reveals a broad vibrationally resolved spectral band, which corresponds to the lead–iron stretching, while the 355 nm spectrum displays many more transitions on the higher-energy side, which correspond to the electronic excited states of PbFe­(CO)₄. Theoretical calculations at the B3LYP level are performed to explore the ground states of both the anionic and neutral PbFe­(CO)₄ and to support spectral identification of the fine resolved photoelectron spectra. Moreover, the unique chemical bonding between lead and iron in PbFe­(CO)₄ is discussed with the aid of natural bond orbital analyses

Structural and Chemical Bonding Properties of AuS₂H^0/–: A Photoelectron Velocity-Map Imaging Spectroscopic and Theoretical Study

Mass-selected photoelectron velocity-map imaging spectroscopy was employed to investigate the geometrical and electronic properties of AuS2H–/0. The comprehensive comparison between the experiment and theoretical calculations establishes that the ground-state AuS2H– anion has a mixed-ligand structure [SAuSH]− with an unsymmetrical S–Au–S unit. Further chemical bonding analyses on AuS2H and comparison with the isoelectronic AuS2– suggest that the unique S–Au–S unit in these species features two three-center, three-electron π-bonding, and one three-center, two-electron σ-bonding. The isoelectronic replacement of the extra electron in AuS2– by the H atom can lead to σ bonding evolution from the electron-sharing bond to the dative bond. These findings are conducive to the fundamental understanding of the intrinsic stability of thiolate-protected gold nanoclusters and their delicate ligand design to achieve desirable properties

Observing the Transition from Equatorial to Axial CO Chemisorption: Infrared Photodissociation Spectroscopy of Yttrium Oxide–Carbonyls

A series of yttrium oxide–carbonyls are prepared via a laser vaporization supersonic cluster source in the gas phase and identified by mass-selected infrared photodissociation (IRPD) spectroscopy in the C–O stretching region and by comparing the observed IR spectra with those from quantum chemical calculations. For YO­(CO)₄⁺, all four CO ligands prefer to occupy the equatorial site of the YO⁺ unit, leading to a quadrangular pyramid with <i>C</i>_4<i>v</i> symmetry. Two energetically nearly degenerate isomers are responsible for YO­(CO)₅⁺, in which the fifth CO ligand is either inserted into the equatorial plane of YO­(CO)₄⁺ or coordinated opposite the oxygen on the <i>C</i>₄ axis. YO­(CO)₆⁺ has a pentagonal bipyramidal structure with <i>C</i>_5<i>v</i> symmetry, which includes five equatorial CO ligands and one axial CO ligand. The present IRPD spectroscopic and theoretical study of YO­(CO)_<i>n</i>⁺ extends the first shell coordination number of CO ligands in metal monoxide carbonyls to six. The transition from equatorial to axial CO chemisorption in these yttrium oxide–carbonyls is fortunately observed at <i>n</i> = 5, providing new insight into ligand interactions and coordination for the transition metal oxides

FeNC catalysts decorated with NiFe₂O₄ to enhance bifunctional activity for Zn–Air batteries

Rechargeable Zn–air battery is a promising next-generation energy storage device attributed to its high energy density, excellent safety, and low cost. However, its commercialization is hampered by sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Herein, we have designed, fabricated, and demonstrated a highly efficient ORR/OER electrocatalyst, NiFe2O4/FeNC, using low-cost materials via a facile synthesis route. NiFe2O4 is successfully loaded on Fe/N-doped carbon (FeNC) through bonding to Fe3C in FeNC. Due to the existence of high ORR active sites such as FeN4 and Fe and N-doped carbon moieties, the half-wave potential of the ORR reaches a high value of 0.83 V. While benefited from NiFe2O4 with high OER activity and the synergistic effect between NiFe2O4 and FeNC, the overpotential is 310 mV at 10 mA cm–2 in the OER. The voltage difference between charging–discharging operations in the Zn–air battery employing the NiFe2O4/FeNC electrocatalyst only increases by 0.16 V after cycling for 100 h (600 cycles) at 10 mA cm–2, which is much lower than 1.28 V using the best commercial Pt/C and RuO2 catalysts. </p

Vibrationally Resolved Photoelectron Imaging of Cu₂H^– and AgCuH^– and Theoretical Calculations

Vibrationally resolved photoelectron spectra have been obtained for Cu₂H^– and AgCuH^– using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu–H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu₂H^– and AgCuH^– to their neutral ground states. The A bands in the spectra of Cu₂H^– and CuAgH^– show stretching progressions of Cu–Cu and Ag–Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu₂H^– and AgCuH^– to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu₂H^– and AgCuH^– and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu₂H^–, AgCuH^–, and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters

Supplementary information files for FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries

Supplementary files for article FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries  Rechargeable Zn–air battery is a promising next-generation energy storage device attributed to its high energy density, excellent safety, and low cost. However, its commercialization is hampered by sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Herein, we have designed, fabricated, and demonstrated a highly efficient ORR/OER electrocatalyst, NiFe2O4/FeNC, using low-cost materials via a facile synthesis route. NiFe2O4 is successfully loaded on Fe/N-doped carbon (FeNC) through bonding to Fe3C in FeNC. Due to the existence of high ORR active sites such as FeN4 and Fe and N-doped carbon moieties, the half-wave potential of the ORR reaches a high value of 0.83 V. While benefited from NiFe2O4 with high OER activity and the synergistic effect between NiFe2O4 and FeNC, the overpotential is 310 mV at 10 mA cm–2 in the OER. The voltage difference between charging–discharging operations in the Zn–air battery employing the NiFe2O4/FeNC electrocatalyst only increases by 0.16 V after cycling for 100 h (600 cycles) at 10 mA cm–2, which is much lower than 1.28 V using the best commercial Pt/C and RuO2 catalysts.  </p