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Synergistic Effect of CO2 in Accelerating the Galvanic Corrosion of Lithium Sodium Anodes in Alkali Metal Carbon Dioxide Batteries
No full textRechargeable alkali metal CO2 batteries, which combine high theoretical energy density and environmentally friendly CO2 fixation ability, have attracted worldwide attention. Unfortunately, their electrochemical performances are usually inferior for practical applications. Aiming to reveal the underlying causes, a combinatorial usage of advanced nondestructive and postmortem characterization tools is used to intensively study the failure mechanisms of Li Na CO2 batteries. It is found that a porous interphase layer is formed between the separator and the Li Na anode during the overvoltage rising and battery performance decaying process. A series of control experiments are designed to identify the underlying mechanisms dictating the observed morphological evolution of Li Na anodes, and it is found that the CO2 synergist facilitates Li Na chemical corrosion, the process of which is further promoted by the unwanted galvanic corrosion and the electrochemical cycling conditions. A detailed compositional analysis reveals that the as formed interphase layers under different conditions are similar in species, with the main differences being their inconsistent quantity. Theoretical calculation results not only suggest an inherent intermolecular affinity between the CO2 and the electrolyte solvent but also provide the most thermodynamically favored CO2 reaction pathways. Based on these results, important implications for the further development of rechargeable alkali metal CO2 batteries are discussed. The current discoveries not only fundamentally enrich our knowledge of the failure mechanisms of rechargeable alkali metal CO2 batteries but also provide mechanistic directions for protecting metal anodes to build high reversible alkali metal CO2 batterie
Radiation hardness of ultrabroadband spintronic terahertz emitters en route to a space qualified terahertz time domain gas spectrometer
No full textThe radiation hardness of ultrabroadband spintronic terahertz emitters against amp; 947; and proton irradiation is investigated. We find that irradiation doses equivalent to those experienced by a space instrument en route to and operated on Mars have a minor effect on the performance of the emitters. In particular, the ultrawide emission spectrum ranging from 0.1 30 amp; 8201;THz, which covers a large part of the vibrational fingerprint region, remains unchanged. These results make this emitter type highly interesting as an essential building block for broadband gas sensors based on terahertz time domain spectroscopy for future space mission
X ray radiation damage cycle of solvated inorganic ions
No full textX ray induced damage is one of the key topics in radiation chemistry. Substantial damage is attributed to low energy electrons and radicals emerging from direct inner shell photoionization or produced by subsequent processes. We apply multi electron coincidence spectroscopy to X ray irradiated aqueous solutions of inorganic ions to investigate the production of low energy electrons LEEs in a predicted cascade of intermolecular charge and energy transfer processes, namely electron transfer mediated decay ETMD and interatomic intermolecular Coulombic decay ICD . An advanced coincidence technique allows us to identify several LEE producing steps during the decay of 1s vacancies in solvated Mg2 ions, which escaped observation in previous non coincident experiments. We provide strong evidence for the predicted recovering of the ion s initial state. In natural environments the recovering of the ion s initial state is expected to cause inorganic ions to be radiation damage hot spots, repeatedly producing destructive particles under continuous irradiatio
Coexisting antiferromagnetic phases on the frustrated pyrochlore sublattice of the mixed Jahn Teller system Ni1 xCuxCr2O4
Get PDFThe magnetic order and phase transitions in the normal spinel system Ni1 xCuxCr2O4 are studied by powder neutron and x ray diffraction, as well as by magnetization measurements to get a complete magnetic phase diagram. For chromites with x Cu gt; 0.5 a canted antiferromagnetic phase of Cr appears first, followed by the onset of ferromagnetism in the Cu sublattice at lower temperature forming a ferrimagnetic lattice. Conversely, with x Cu lt; 0.5 the ferrimagnetic order between the Cr and Cu spins occurs at the higher ordering temperature followed by the onset of antiferromagnetic order in the Cr sublattice. Apart from the crossing of the two boundary lines of the transition temperatures at x Cu 0.50 a compensation point of the ferrimagnetic moments is determined at x Cu 0.60, where the spontaneous magnetization has almost completely vanished. Most remarkable is the antiferromagnetic Cr ordering on the orthorhombic distorted pyrochlore lattice for samples in the x Cu range from 0 to 0.12 due to the large variety of coexisting magnetic phases. In the magnetic ground state of NiCr2O4 two commensurate antiferromagnetic structures with the propagation vectors kAF 0,0,1 and , , coexist. With increasing Cu content from x Cu 0 to 0.09 these phases undergo a transition to another commensurate structure with k 0 via two coexisting incommensurate magnetic phases with the vectors kIC1 0,0,kz and kIC2 0,ky,kz . The different magnetic phases are discussed qualitatively based on the lattice dimensions depending on the concentration ratio of two Jahn Teller ions at the tetrahedral A site, where Ni2 causes elongated and Cu2 compressed tetragonal lattice distortions. Further, magnetoelasticity studies on selected samples indicate that the magnetically induced lattice strains follow the symmetry of the underlying Jahn Teller distorted lattice
K Doping Suppresses Oxygen Redox in P2 Na0.67Ni0.11Cu0.22Mn0.67O2 Cathode Materials for Sodium Ion Batteries
No full textIn P2 type layered oxide cathodes, Na site regulation strategies are proposed to modulate the Na distribution and structural stability. However, their impact on the oxygen redox reactions remains poorly understood. Herein, the incorporation of K in the Na layer of Na0.67Ni0.11Cu0.22Mn0.67O2 is successfully applied. The effects of partial substitution of Na with K on electrochemical properties, structural stability, and oxygen redox reactions have been extensively studied. Improved Na diffusion kinetics of the cathode is observed from galvanostatic intermittent titration technique GITT and rate performance. The valence states and local structural environment of the transition metals TMs are elucidated via operando synchrotron X ray absorption spectroscopy XAS . It is revealed that the TMO2 slabs tend to be strengthened by K doping, which efficiently facilitates reversible local structural change. Operando X ray diffraction XRD further confirms more reversible phase changes during the charge discharge for the cathode after K doping. Density functional theory DFT calculations suggest that oxygen redox reaction in Na0.62K0.03Ni0.11Cu0.22Mn0.67O2 cathode has been remarkably suppressed as the nonbonding O 2p states shift down in the energy. This is further corroborated experimentally by resonant inelastic X ray scattering RIXS spectroscopy, ultimately proving the role of K incorporated in the Na laye
Nanocrystal residual strains and density layers enhance failure resistance in the cleithrum bone of evolutionary advanced pike fish
Get PDFFailure resistant designs are particularly crucial for bones subjected to rapid loading, as is the case for the ambush hunting northern pike Esox lucius . These fish have slim and low density osteocyte lacking bones. As part of the swallowing mechanism, the cleithrum bone opens and closes the jaw. The cleithrum needs sufficient strength and damage tolerance, to withstand years of repetitive rapid gape and suck cycles of feeding. The thin wing shaped bone comprises anisotropic layers of mineralized collagen fibers that exhibit periodic variations in mineral density on the mm and micrometer length scales. Wavy collagen fibrils interconnect these layers yielding a highly anisotropic structure. Hydrated cleithra exhibit Young s moduli spanning 3 9 GPa where the yield stress of amp; 8764;40 MPa increases markedly to exceed amp; 8764;180 MPa upon drying. This 5x observation of increased strength corresponds to a change to brittle fracture patterns. It matches the emergence of compressive residual strains of amp; 8764;0.15 within the mineral crystals due to forces from shrinking collagen layers. Compressive stresses on the nanoscale, combined with the layered anisotropic microstructure on the mm length scale, jointly confer structural stability in the slender and lightweight bones. By employing a range of X ray, electron and optical imaging and mechanical characterization techniques, we reveal the structure and properties that make the cleithra impressively damage resistant composite
Benchmarking microwave induced CO2 plasma splitting against electrochemical CO2 reduction for a comparison of promising technologies
Get PDFPlasma conversion technology is an emerging technique under development to activate, convert or valorize gas molecules such as CO2, N2, CH4, NH3 and others. A large scale application beyond the lab scale demonstrator unit requires assessment of the efficiency of this new technology. The straightforward approach for assessment of the efficiency is benchmarking with the other well established technologies of similar technology readiness level TRL . In this paper we present a benchmarking of the atmospheric pressure microwave induced CO2 plasma splitting with electrochemical CO2 conversion, via both low temperature and high temperature electrolysis. An additional step of oxygen removal in case of the plasma reactor is implemented due to the difference in the output stream of the plasma gas mixture containing CO2, CO, and O2 and the electrochemical reactor typical gas mixture on cathode containing CO2 and CO . For the benchmarking, a comprehensive set of comparison parameters that are applicable for both the plasma and the electrochemical route is identified and grouped in three comparison categories performance, interfaces, and economics. The comparison of these parameters demonstrates that in terms of the electric power consumption EPC; power required for production of one Nm3CO plasma conversion technology amp; 8764;20 kWh Nm3CO is in the ballpark with the other two electrochemical technologies amp; 8764;4 20 kWh Nm3CO . The key features of the plasma conversion technology are relatively large conversion up to 56 and moderate energy efficiencies up to 27 . Also, CO2 gas of reduced purity of only 98 can be used without decrease of the performance, and CO output values are currently at 3.5 slm standard litre per minute . Fast on off response time of order of minutes, and no need for the hot standby indicate that the plasma conversion is particularly suitable for use of intermittent renewable energy sources. The aspects that require further development include optimization of the process towards lower EPCtotal values, improved oxygen gas separation, and reliable ignition of the plasm
Experimental determination of the hafnium L subshell fundamental parameters using the holistic approach
Get PDFBy employing the recently demonstrated new holistic approach, the atomic fundamental parameters FPs of the three Hf L subshells were experimentally determined using the radiometrically calibrated instrumentation of the Physikalisch Technische Bundesanstalt. The Coster Kronig factors, the L subshell fluorescence yields, the L subshell Auger yields, the subshell photoionization cross sections, and the subshell fluorescence production cross sections were determined by means of photon energy dependent x ray fluorescence and transmission measurements. The recently demonstrated new holistic evaluation approach allows to determine the FPs with significantly lower uncertainties as compared to the former data evaluation scheme, where only a limited regime of incident photon energies is being probed and the data evaluation scheme is performed in a sequential manne
MnFeNi based composite as a case study of a bifunctional oxygen electrocatalyst under dynamically changing electrode potentials
Get PDFHigh performance bifunctional electrocatalysts for the oxygen reduction ORR and oxygen evolution reaction OER are essential components in energy conversion and storage technologies. Yet, their poor reversibility hinders their applicability. A highly active ORR OER catalyst, consisting of multiwalled carbon nanotubes supported MnFeNiOx nanoparticles, was subjected to sequences of chronoamperometric steps alternating between the ORR, the OER and highly cathodic potentials Ec . Rotating ring disk electrode methods revealed that applying Ec leads to a small increase in the current and peroxide species yield during the ORR while enhancing substantially the OER. X ray absorption spectroscopy showed irreversible changes in the chemical state of MnFeNiOx correlating with its catalytic properties. The complexity of changes that a composite catalyst may undergo under varying potentials, the importance of monitoring product formation, and the convenience of using dynamic electrochemical sequences for the assessment of catalyst reversibility, as well as for the activation and or restoration of their catalytic properties, are highlighte
Growth and Structure of Ultrathin Iron Silicate and Iron Germanate Films
No full textThe growth and structure of two dimensional iron silicate and iron germanate films on Ru 0001 are studied. We investigate in detail the temperature dependent film formation of ultrathin layers of iron silicate and iron germanate. These two dimensional films can be seen as model systems for more complex catalytically active structures, such as zeolites, which can be used as selective catalysts or molecular sieves. The experimental methods of XPS, LEED, LEEM, LEEM IV, and XPEEM are applied for correlated chemical and physical characterization in situ and in real time, and DFT is applied for theoretical consideration. We show that both systems can be considered as two layered systems, with a monolayer of iron oxide at the Ru interface and a monolayer of silica or germania on top, respectively. The Fe Fe distance in the iron oxide layer is influenced by the Si O Si or Ge O Ge bond length, in agreement with those of unstrained silicates or germanates. Moreover, iron silicate can be prepared using different preparation methods. The actual loading of Fe atoms is three per unit cell for FeGeOx and only two for FeSiO