Huanying Liu

Remarkable dependence of electrochemical performance of SrCo0.8Fe0.2O3-δ on A-site nonstoichiometry

SrCo(0.8)Fe(0.2)O(3-δ) is a controversial material whether it is used as an oxygen permeable membrane or as a cathode of solid oxide fuel cells. In this paper, carefully synthesized powders of perovskite-type Sr(x)Co(0.8)Fe(0.2)O(3-δ) (x = 0.80-1.20) oxides are utilized to investigate the effect of A-site nonstoichiometry on their electrochemical performance. The electrical conductivity, sintering property and stability in ambient air of Sr(x)Co(0.8)Fe(0.2)O(3-δ) are critically dependent on the A-site nonstoichiometry. Sr(1.00)Co(0.8)Fe(0.2)O(3-δ) has a single-phase cubic perovskite structure, but a cobalt-iron oxide impurity appears in A-site cation deficient samples and Sr(3)(Co, Fe)(2)O(7-δ) appears when there is an A-site cation excess. It was found that the presence of the cobalt-iron oxide improves the electrochemical performance. However, Sr(3)(Co, Fe)(2)O(7-δ) has a significant negative influence on the electrochemical activity for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The peak power densities with a single-layer Sr(1.00)Co(0.8)Fe(0.2)O(3-δ) cathode are 275, 475, 749 and 962 mW cm(-2) at 550, 600, 650 and 700 °C, respectively, values which are slightly lower than those for Sr(0.95)Co(0.8)Fe(0.2)O(3-δ) (e.g. 1025 mW cm(-2) at 700 °C) but much higher than those for Sr(1.05)Co(0.8)Fe(0.2)O(3-δ) (e.g. only 371 mW cm(-2) at 700 °C). This remarkable dependence of electrochemical performance of the Sr(x)Co(0.8)Fe(0.2)O(3-δ) cathode on the A-site nonstoichiometry reveals that lower values of electrochemical activity reported in the literature may be induced by an A-site cation excess. Therefore, to obtain a high performance of Sr(x)Co(0.8)Fe(0.2)O(3-δ) cathode for IT-SOFCs, an A-site cation excess must be avoided.

Atomic-scale topochemical preparation of crystalline Fe3+-doped β-Ni(OH)2 for an ultrahigh-rate oxygen evolution reaction

The development of highly efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) has been considered as a great challenge to the practical applications for water splitting and in rechargeable metal–air batteries. Herein, we report active and robust OER catalysts of Fe3+-doped β-Ni(OH)2 prepared via an atomic-scale topochemical transformation route. Based on the premise that all Fe3+ is incorporated into the β-Ni(OH)2 lattice, the OER activity increases directly with the content of Fe3+. The Fe(0.5)-doped β-Ni(OH)2 catalyst affords a current density of 10 mA cm−2 at an overpotential as low as 0.26 V and a small Tafel slope of 32 mv dec−1. Comparing the state-of-the-art IrO2 catalyst, the Fe(0.5)-doped β-Ni(OH)2 catalyst exhibits higher activity and stability from galvanostatic tests at 10 mA cm−2. Additionally, we experimentally demonstrate that Fe(0.5)-doped β-Ni(OH)2 exerts higher OER activity than Fe(0.5)-doped α-Ni(OH)2. All evidence indicates that Fe and the β-Ni(OH)2 matrix play an important role in NiFe-based catalysts.

Signatures of the projectile electron–target core elastic scattering in Ar (e, 2e) reactions at low and intermediate impact energies

The momentum distributions of the recoil ions Ar+ in Ar (e, 2e) reactions are obtained at incident electron energies from 80 to 220 eV by using the reaction microscope. The contributions of large longitudinal momentum corresponding to the large scattering angle are significant. By comparing the single differential cross sections of the Ar (e, 2e) with those of the electron–argon elastic scattering process, it is concluded that the elastic scattering between the incident electron and the target core plays an important role in the large angle ionization scattering process, and the additional phase shift introduced by the ionized electron results in the disappearance of the sharp minimum that was observed in the elastic scattering. A qualitative explanation of the bigger relative contributions of recoil ions with large longitudinal momenta in Ne (e, 2e) compared to the case in Ar (e, 2e) is given.

Studies of laser induced-breakdown spectroscopy of holly leaves

The LIBS spectra of holly leaves produced by Nd:YAG nanosecond laser has been investigated. More than 20 elements and molecules were identified from the spectra. The influence of laser wavelength upon analysis of plant samples via LIBS technique has been investigated. The comparison of LIBS spectra shows that the spectrum for 1064 nm irradiation is more intense than the one for 266 nm irradiation by the same pulse energy in the near-UV region. Investigation of the influence of laser wavelength for LIBS can help to improve the analytical capabilities of LIBS.

High negative ion production yield in 30 keV F2+ + adenine (C5H5N5) collisions

In collisions between slow F2+ ions (30 keV) and molecular targets, adenine, scattered particle production yields have been measured directly by simultaneous detection of neutrals, positive and negative ions. The relative cross-section for a negative ion formation channel was measured to be 1%. Despite a slight decrease compared to a larger target, the fullerene C60, the measured negative ion formation cross section is still at least one order of magnitude larger than the yield in ion–atom interactions.

New insight into power-law behavior of fragment size distributions in the C60 multifragmentation regime

Previous experimental work has shown that a phase transition in C60 multifragmentation induced by nanosecond laser occurs at almost constant temperature covering a wide range of laser fluency. Here the relative yields of ionic fragments (IFs) C(n)(+) (n = 1-20) resulting from the multifragmentation are measured within the phase transition region. By excluding two small IFs and magic IFs due to their abnormal behavior, the data for residual IFs are used to estimate the size distributions of primary intermediate-mass IFs in the multifragmentation regime. The distributions are found to obey power laws n(-τ). Furthermore, the exponent τ values have sensitive dependence on lower laser fluency and converge to a constant of about 2.4 ± 0.2 for larger fluencies. These observations are in good agreement with an explanation based on the Fisher droplet model, offering the tantalizing possibility of a liquid-to-gas phase transition in C60 systems.

A newly built setup for small bio-molecule fragmentation study in Lanzhou

A new setup for studying ion induced small bio-molecule fragmentation processes has been built in Lanzhou, China. A preliminary collision experiment between a 30 keV He2+ ion beam and gas phase adenine molecules was performed. Partial TOF spectra associated to well-defined scattered projectile final charge states, He+ or He0 were recorded. Coincidence spectra between fragments were also obtained.

Progress of highly charged atomic physics at IMP

The progress of atomic physics researches at the Institute of Modern Physics (IMP) is reviewed, covering the studies on ion-atom/molecule collisions, ion-cluster interaction, negative ion formation, state-selective electron capture studied by COLTRIMS, as well as the progress of a new experimental area dedicated for atomic researches at moderate energies, and the advances of the cooler storage rings at the Heavy Ion Research Facility in Lanzhou (HIRFL). New opportunities to study collision dynamics from femto-second to atto-second regime are opened based on the present facilities and the on-going projects.

An experimental investigation of the dissociative ionization process of argon cluster ions induced by electron impact

Utilizing the Cold Target Recoil Ions Momentum Spectrometer (COLTRIMS), dissociative ionization of argon cluster was experimentally investigated by electron impact. The recoil ions produced both in the pure ionization process and the dissociative ionization channels are measured with collision energies from 100 and 1000 eV. The ratios of the dimer ions from pure ionization (Ar2P+) and the dimer ions from small cluster dissociation (Ar+2D) to the atomic argon ion (Ar+) in different stagnation pressures were obtained.

Dynamics of transfer ionization process in p-He collisions at intermediate energies

Using the reaction microscope technique, we have performed a kinematically complete experiment on transfer ionization in 50 to 100 keV proton-helium collisions. A careful inspect on the momentum balance provides insight into the dynamics of the transfer ionization process.