GENFIRE: A generalized Fourier iterative reconstruction algorithm for high-resolution 3D imaging

Tomography has made a radical impact on diverse fields ranging from the study of 3D atomic arrangements in matter to the study of human health in medicine. Despite its very diverse applications, the core of tomography remains the same, that is, a mathematical method must be implemented to reconstruct the 3D structure of an object from a number of 2D projections. In many scientific applications, however, the number of projections that can be measured is limited due to geometric constraints, tolerable radiation dose and/or acquisition speed. Thus it becomes an important problem to obtain the best-possible reconstruction from a limited number of projections. Here, we present the mathematical implementation of a tomographic algorithm, termed GENeralized Fourier Iterative REconstruction (GENFIRE). By iterating between real and reciprocal space, GENFIRE searches for a global solution that is concurrently consistent with the measured data and general physical constraints. The algorithm requires minimal human intervention and also incorporates angular refinement to reduce the tilt angle error. We demonstrate that GENFIRE can produce superior results relative to several other popular tomographic reconstruction techniques by numerical simulations, and by experimentally by reconstructing the 3D structure of a porous material and a frozen-hydrated marine cyanobacterium. Equipped with a graphical user interface, GENFIRE is freely available from our website and is expected to find broad applications across different disciplines.Comment: 18 pages, 6 figure

Multi‐Component PtFeCoNi Core‐Shell Nanoparticles on MWCNTs as Promising Bifunctional Catalyst for Oxygen Reduction and Oxygen Evolution Reactions

The development of commercially viable fuel cells and metal-air batteries requires effective and cheap bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Multi-component Pt−Fe−Co−Ni nanoparticles on multi-walled carbon nanotubes (MWCNTs) were synthesized by wet chemistry route via NaBH$_4$ reduction of metal salts, followed by sintering at different temperatures. The catalyst demonstrates an excellent ORR activity and a promising OER activity in 0.1 m KOH, with a bi-functional over-potential, ΔE of 0.83 V, which is comparable to the values of Pt/C or RuO$_2$. Furthermore, it shows outstanding long-term stability in ORR and OER, namely diffusion limited current density at a potential of 0.3 V decreased just by 5.5 % after 10000 cycles in ORR. The results of the PFCN@NT$^{300}$ indicate a significant effect of the substitution of Pt by the transition metal (TM) and the formation of nanoparticles on the catalytic performance, especially in the OER

Ionothermal synthesis of activated carbon from waste PET bottles as anode materials for lithium-ion batteries

Waste polyethylene terephthalate (PET) bottles have become a significant post-consumer plastic waste with attendant environmental problems. Hence, ionothermal synthesis has been used to prepare activated carbon (AC) anode materials from waste PET for both high performance and sustainable lithium-ion batteries (LIB). Particularly, using choline chloride deep eutectic salts (CU-DES) does not require post-synthesis washing and thereby reduces the complexity of the process and produces materials with unique low-surface area, higher levels of graphitization/ordering, and high nitrogen doping in the obtained ACs. The results show that the AC produced using CU-DES (PET-CU-A-ITP2) gave good electrochemical performance. Even though the material possesses a low surface area (∼23 m2 g−1), it displays a gravimetric capacity (GC) of ∼460 mA h g−1 and a coulombic efficiency (CE) of ∼53% in the 1st cycle and very good cycling performance with a capacity retention of 98% from the 2nd to the 100th cycle. The superior electrochemical performance of the PET-CU-A-ITP2 anode was found to be due to its better graphitization/ordering and dense structure which results in higher capacity, formation of less solid electrolyte interphase, and higher CE. These results show that dense carbons can be exploited as high-performance anodes in LIBs. Also, this research presents both a pathway for waste PET management and a waste-energy approach that could offer cheaper and greener LIBs to meet the sustainable development goals

Investigation of Structural and Electronic Changes Induced by Postsynthesis Thermal Treatment of LiNiO2_{2}

Postsynthesis thermal treatments at various temperatures in air have been applied to LiNiO2, and the induced structural and electronic changes have been uncovered. Except for the familiar decomposition process at higher temperatures, a series of transformations also take place under mild conditions. To identify such subtle changes, ex situ and in situ synchrotron radiation diffraction, ex situ7Li nuclear magnetic resonance spectroscopy, and ex situ measurements of magnetic properties have been performed. We show that the reaction between LiNiO2 and CO2 starts already at a temperature of 200 °C, forming Li1–zNi1+zO2 layers. If the thickness of this layer is well adjusted, the electrochemical performance of LiNO2 can be improved. A cation off-stoichiometry of [Li0.90Ni0.10]NiO2 is identified at 600 °C even before the decomposition occurs. We also investigate the interplay of the reaction between LiNiO2 and CO2 with the decomposition at 700 °C. The changes in the Ni oxidation state and local Li environments are also monitored during the whole process

The Impact of Microstructure on Filament Growth at the Sodium Metal Anode in All‐Solid‐State Sodium Batteries

In recent years, all-solid-state batteries (ASSBs) with metal anodes have witnessed significant developments due to their high energy and powerdensity as well as their excellent safety record. While intergranular dendriticlithium growth in inorganic solid electrolytes (SEs) has been extensively studied for lithium ASSBs, comparable knowledge is missing forsodium-based ASSBs. Therefore, polycrystalline Na-′′-alumina is employedas a SE model material to investigate the microstructural influence on sodiumfilament growth during deposition of sodium metal at the anode. The research focuses on the relationship between the microstructure, in particular grainboundary (GB) type and orientation, sodium filament growth, and sodium iontransport, utilizing in situ transmission electron microscopy (TEM) measurements in combination with crystal orientation analysis. The effect ofthe anisotropic sodium ion transport at/across GBs depending on theorientation of the sodium ion transport planes and the applied electric field on the current distribution and the position of sodium filament growth is explored. The in situ TEM analysis is validated by large field of viewpost-mortem secondary ion mass spectrometer (SIMS) analysis, in which sodium filament growth within voids and along grain boundaries is observed, contributing to the sodium network formation potentially leading to failure of batteries

High-entropy spinel-structure oxides as oxygen evolution reaction electrocatalyst

High-entropy oxides are an upcoming research topic due to their broad range of possible crystal structures and applications. In this work, we want to present the change in the catalytic properties when using different elements to create a high-entropy spinel. Therefore, we used the nebulized-spray pyrolysis to synthesize the high-entropy spinel (Mn$_{0.2}$Fe$_{0.2}$Ni$_{0.2}$Mg$_{0.2}$Zn$_{0.2}$)$_{3}$O$_{4}$ and later on exchanged the Mg or the Zn with elements with multiple possible oxidation states, in our example each with Cr or Co. The phase purity, morphology, microstructure and homogeneity were investigated by XRD, SEM and STEM-EDX. Their electrocatalytic performance and stability was measured via oxygen evolution reaction and cyclic voltammetry and compared to IrO$_{2}$, used as reference. The best performance of the synthesized materials was achieved by (Mn$_{0.2}$Fe$_{0.2}$Ni$_{0.2}$Mg$_{0.2}$Cr$_{0.2}$)$_{3}$O$_{4}$