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Li Cations Activate NiFeOOH for Oxygen Evolution in Sodium and Potassium Hydroxide
Get PDFThe efficiency of electrolysis is reduced due to the sluggish oxygen evolution reaction OER . Besides catalyst properties, electrocatalytic activity also depends on the interaction of the electrocatalyst with the electrolyte. Here, we show that the addition of small amounts of Li to Fe free NaOH or KOH electrolytes activates NiFeOOH for the OER compared to single cation electrolytes. Moreover, the activation was maintained when the solution was returned to pure NaOH. Importantly, we show that the origin of activation by Li cations is primarily non kinetic in nature, as the OER onset for the mixed electrolyte does not change and the Tafel slope at low current density is 30 amp; 8197;mV dec in both electrolytes. However, the increase of the apparent Tafel slope remains lower at increasing current densities in the presence of Li . Based on electrochemical quartz crystal microbalance and in situ X ray absorption spectroscopy measurements, we show that this reduction of non kinetic effects is due to enhanced intercalation of sodium, water and hydroxide. This enhanced electrolyte penetration facilitates the OER, especially at higher current densities and for increased catalyst loading. Our work shows that mixed electrolytes where distinct cations can have different roles provide a simple and promising strategy towards improved OER rate
The Role of the Lowest Excited Triplet State in Defining the Rate of Photoaquation of Hexacyanometalates
Get PDFPhotosolvation is a type of ligand substitution reaction started by irradiation of a solution with light, triggering the replacement of a ligand with a molecule from the solvent. The excited state is created through many possible pathways. For the class of hexacyanides of groups 8 and 9 of the periodic table, irradiation in the ligand field band is followed by intersystem crossing to the lowest excited triplet state, which we propose to mediate the photoaquation reaction in this class of complexes. In this study, we present time resolved X ray absorption data showing indications of the triplet intermediate state in the cobalt III hexacyanide complex and we discuss general aspects of the photoaquation reaction in comparison with reported data on the isoelectronic iron II hexacyanide. Quantum chemical calculations are analyzed and suggest that the nature of the lowest excited triplet state in each complex can explain the drastically different rate of reactions observe
Tuning Electronegativity Difference Configuration to Construct Non Bonded O 2p Orbitals for Reversible Anionic Redox in O3 Type Cathode
No full textHow to tune the activity and reversibility of oxygen anion redox OAR is a critical issue for O3 type sodium ion battery SIB cathodes. Herein, the key role of electronegativity difference configuration on the activation of OAR is find out, and further tune electronegativity difference configuration with La incorporation to construct non bonded O 2p orbitals and achieve the reversible anionic redox in O3 type NaMn1 3Fe1 3Ni1 3O2. Owing to the special extranuclear electronic structure of La3 [Xe], the La electron cloud is difficult to be disturbed by the O electron cloud, and some O electrons do not participate in the formation of ionic bonds, thus retaining the non bonded electrons of O 2p and activating OAR. Moreover, La3 doping also decreases the Coulomb force between Na and O2 amp; 8722; favoring Na migration as well as strengthening the La amp; 9472;O bonds inhibiting the irreversible phase transition. La2O3 coating layer also plays a role on inhibiting the reaction between molecular oxygen and the electrolyte, and making OAR reversible. After modification, the cycling stability is significantly improved 86.9 vs 27.3 2C 200cycles; 90.8 vs 52.9 5C 300 cycles . This study presents some insights on OAR activation mechanism and offers a facile strategy to improve the activity and reversibility of OAR for designing high performance SIBs cathode
Progress and Perspective of Controlling Li Dendrites Growth in All Solid State Li Metal Batteries via External Physical Fields
Get PDFLi dendrites penetration through solid electrolytes SEs challenges the development of solid state Li batteries SSLBs . To date, significant efforts are devoted to understand the mechanistic dynamics of Li dendrites nucleation, growth, and propagation in SEs, and various strategies that aim to alleviate and even inhibit Li dendrite formation have been proposed. Nevertheless, most of these conventional strategies require either additional material processing steps or new materials layers that eventually increase battery cost and complexity. In contrast, using external fields, such as mechanical force, temperature physical field, electric field, pulse current, and even magnetic field to regulate Li dendrites penetration through SEs, seems to be one of the most cost effective strategies. This review focuses on the current research progress of utilizing external physical fields in regulating Li dendrites growth in SSLBs. For this purpose, the mechanical properties of Li and SEs, as well as the experimental results that visually track Li penetration dynamics, are reviewed. Finally, the review ends with remaining open questions in future studies of Li dendrites growth and penetration in SEs. It is hoped this review can shed some light on understanding the complex Li dendrite issues in SSLBs and potentially guide their rational design for further developmen
Non invasive 3D analysis of microplastic particles in sandy soil Exploring feasible options and capabilities
Get PDFIncreasingly, environmental research efforts seek to understand how the continuous input of microplastics into terrestrial environments alters soil physicochemical properties and affects plants and other soil biota. However, fundamental understanding is hampered by the destructive nature of current analytical techniques, which typically require the disruption of soil samples and often the removal of soil organic matter. This results in the irretrievable loss of essential information about soil microstructure and the spatial distribution of microplastic particles. We showed that the non invasive approach of dual neutron and X ray tomography is capable of detecting and localizing microplastics embedded in soil environments with organic components, here tested with peat, charcoal, and bark mulch additions. We explored how the number of microplastic particles can be determined on intact samples, even accompanied by add on information on the size, shape and distribution of microplastic particles. For some combinations of plastic types and organic material amendments, the basic approach was not successful, but could be enhanced by soaking the sample in hydrogen peroxide solution while largely preserving the integrity of the microstructure, or by including shape parameters into the image analysis. By segmenting images using region growing, we were able to identify all microplastic particles without false positives, even in the presence of organic material. We also succeeded in analyzing small sized microplastic particles, such as film or fibers, embedded in natural sandy soil. 3D visualization of plastic film fragments together with the soil matrix made it obvious that larger fragments can have a significant impact on soil hydraulic properties. It has also been shown that a group of microplastic fibers can induce a planar crack in the soil matrix. Finally, roots and microplastics could be differentiated and visualized in a soil sample, demonstrating the leeway for the non invasive study of potential interactions between roots and microplastic
A Metal Organic Framework Derived Strategy for Constructing Synergistic N Doped Carbon Encapsulated NiCoP N C Based Anodes toward High Efficient Lithium Storage
No full textTransition metal phosphides TMPs have been regarded as the prospective anodes for lithium ion batteries LIBs . However, their poor intrinsic conductivity and inevitable large volume variation result in sluggish redox kinetics and the collapse of electrode structure during cycling, which substantially hinders their practical use. Herein, an effective composite electrodes design strategy of assembly and phosphorization is proposed to construct synergistic N doped carbon encapsulated NiCoP N C based composites, employing a metal organic frameworks MOFs as sacrificial hosts. Serving as the anodes for LIBs, one representative P NCP NC 600 electrode exhibits high reversible capacity 858.5 mAh g amp; 8722;1, 120 cycles at 0.1 A g amp; 8722;1 and superior long cycle stability 608.7 mAh g amp; 8722;1, 500 cycles at 1 A g amp; 8722;1 . The impressive performances are credited to the synergistic effect between its unique composite structure, electronic properties and ideal composition, which achieve plentiful lithium storage sites and reinforce the structural architecture. By accompanying experimental investigations with theoretical calculations, a deep understanding in the lithium storage mechanism is achieved. Furthermore, it is revealed that a more ideal synergistic effect between NiCoP components and N doped carbon frameworks is fundamentally responsible for the realization of superb lithium storage properties. This strategy proposes certain instructive significance toward designable high performance TMP based anodes for high energy density LIB
Metastable nickel oxygen species modulate rate oscillations during dry reforming of methane
No full textWhen a heterogeneous catalyst is active, it forms metastable structures that constantly transform into each other. These structures contribute differently to the catalytic function. Here we show the role of different metastable oxygen species on a Ni catalyst during dry reforming of methane by combining environmental scanning electron microscopy, near ambient pressure X ray photoelectron spectroscopy, on line product detection and computer vision. We highlight the critical role of dissociative CO2 adsorption in regulating the oxygen content of the catalyst and in CH4 activation. We also discover rate oscillations during dry reforming of methane resulting from the sequential transformation of metastable oxygen species that exhibit different catalytic properties atomic surface oxygen, subsurface oxygen and bulk NiOx. The imaging approach allowed the localization of fluctuating surface regions that correlated directly with catalytic activity. The study highlights the importance of metastability and operando analytics in catalysis science and provides impetus towards the design of catalytic system
High efficiency multilayer coated laminar gratings with high line density for tender X ray region
Get PDFDriven by the demand of high efficiency and high resolution monochromators and spectrometers in the tender X ray range, high line density multilayer coated laminar gratings MLLG were designed, manufactured, and analyzed. Theoretical simulations displayed that a 5000 l mm MLLG could realize high resolution at 3 keV and 40 times higher diffraction efficiency than the single layer coated grating. For the first demonstration of the high line density MLLGs, two 3000 l mm laminar gratings were fabricated and coated by Cr C multilayers with different periodic thicknesses to achieve high efficiency HE and high resolution HR performance. For MLLGHE, a maximum efficiency of 54.5 was achieved at 4.4 keV. For MLLG HR, relatively high efficiency of 23.1 38.6 were demonstrated with much stronger asymmetric diffraction in 2 4 keV, which can significantly increase the energy resolution of the syste
Electrodeposition of copper on niobium for cryocooler application
Get PDFThe electrodeposition of copper onto niobium using commercial acidic and alkaline electrolytes was tested. The continuous dense polycrystalline copper films were successfully obtained in aqueous alkaline type bath containing copper sulphate, sodium hydroxide and sodium gluconate. The effect of benzotriazole and sodium lauryl sulphate additives on the morphology and crystal structure of the deposited copper was investigated by optical and scanning electron microscopy, and X ray diffraction. No copper oxides were found in the grown films. Copper films had moderate adhesion properties that would be insufficient for cryocooler application. We are currently exploring different compositions of electrolyte baths for obtaining the coatings on niobium with improved adhesio
Solid Electrolyte Interphase Formation on Anatase TiO2 Nanoparticle Based Electrodes for Sodium Ion Batteries
Get PDFCarbon coated anatase TiO2 nanoparticles are a promising anode material for sodium ion batteries, theoretically providing a satisfactory capacity combined with a relatively low cost, environmental friendliness, and high rate capability. Nondestructive, depth resolved hard X ray photoelectron spectroscopy HAXPES is exploited to reveal the composition profile of the solid electrolyte interphase SEI that forms during the first sodiation discharge cycle and that has been determined to be on average 6 nm thick. Sodium chloride NaCl , sodium fluoride NaF , sodium carbonate Na2CO3 , sodium alkyl carbonates NaCO3 R , poly ethylene oxide PEO , sodium hydroxide NaOH , sodium ions, and hydrocarbons have been identified as the major species within the SEI, with a higher hydrocarbon concentration near the SEI electrode interface and a higher sodium ion concentration at the SEI surface. These findings give detailed insights into the complex interplay taking place at the electrolyte TiO2 nanoparticle interface during the sodiation desodiation discharging charging processes, paving the way for a deliberate optimizatio