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p-Block Metal Oxide Noninnocence in the Oxygen Evolution Reaction in Acid: The Case of Bismuth Oxide
The Pourbaix diagrams of p-block Pb, Sb, and Bi establish a robust stability for their oxides in acidic solutions. Such oxides have found utility as stable frameworks to support metals that are active for oxygen evolution reaction (OER) catalysis, but they also possess two-electron redox couples, which can potentially engender OER activity. Thus, the use of p-block oxide supports provides an imperative for understanding the OER activity of the unary oxides. Toward this end, we report BiO x films that are able to perform OER catalysis at moderate overpotentials for extended periods of operation (>110 h) in highly acidic solutions (pH 1.0–2.25) with no sign of decreased OER activity during operation at current densities of 1–5 mA cm –2 . X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and UV-vis spectroelectrochemistry reveal a change in the Bi oxidation state prior to OER catalysis, from predominantly Bi 3+ in the as-deposited films to primarily Bi 5+ in the catalytically active films. Furthermore, this transformation is accompanied by a prominent color change from orange to dark brown. Simulations of the cyclic voltammogram catalytic profiles suggest two OER pathways for BiO x involving Bi IV O x and Bi V O x catalysts with the Bi V O x pathway prevailing after catalyst activation. Together, these results demonstrate the ability of BiO x to facilitate OER in acid with high functional stability and underscore the noninnocent role that p-block metal oxides may play in OER catalysis in acidic media.
Chemical Challenges that the Peroxide Dianion Presents to Rechargeable Lithium–Air Batteries
Understanding the fundamental redox reactions and processes that occur in lithium–air and, more generally, metal–air batteries is important to the progress of this promising energy-storage technology. Knowledge of the chemistry of the peroxide dianion, O 2 2– , is especially crucial, as the dianion is at the nexus of the charge/discharge cycle of lithium–air batteries. The intrinsic electron transfer properties and redox chemistry of peroxide dianion are poorly defined because it is difficult to isolate the dianion free of protons and metal ions. We review the results of (i) the electron transfer kinetics and (ii) the redox reaction chemistry of isolated peroxide dianion encapsulated within the cavity of a hexacarboxamide cryptand. With regard to the former, electron transfer kinetics measurements provide fundamental Marcus parameters that will be useful for models that seek to disentangle the precise contributions of Li + ion-coupled electron transfer, electron transfer across the Li 2 O 2 solid particle interface, and charge hopping among Li 2 O 2 particles. With regard to the latter, an underappreciated chemistry of peroxide dianion with CO 2 produces peroxymonocarbonate (OOCO 2 2– ) and peroxydicarbonate (O 2 COOCO 2 2– ). An autocatalytic cycle will lead to oxidative degradation of traditional organic electrolytes and other vulnerable cell components employed in lithium–air batteries. Furthermore, this peroxycarbonate-derived chemistry, in addition to more commonly recognized solution-based oxidation chemistry, will need to be mitigated to realize the long-term cyclability of rechargeable lithium–air batteries.
Electrolyte-Induced Restructuring of Acid-Stable Oxygen Evolution Catalysts
Crystalline metal oxide catalysts operating under oxygen evolution reaction (OER) conditions invariably restructure, resulting in active sites with hydroxo/oxo species in an amorphous environment. An increase in the population of terminal hydroxo/oxo species (i.e., edge sites) facilitates proton-coupled electron-transfer (PCET) kinetics for oxygen generation and thus improves catalyst competency. While amorphous films benefit from a greater density of active sites, they suffer from diminished charge transport as compared to that of extended crystalline lattices. Managing this amorphous–crystalline dichotomy is essential when designing OER catalysts, which we highlight with the examination of electrodeposited PbO x materials, which historically are very poor OER catalysts. Along these lines, the presence of phosphate during PbO x electrodeposition truncates the growth of an extended lattice owing to its strong bonding to oxide surfaces to afford an amorphous catalyst film (A-PbO x ) with significant charge-transfer resistance (138 ± 42 Ω) and poor OER kinetics (420 ± 105 mV dec –1 Tafel slope). Conversely, electrodeposition of Pb 2+ in the presence of less coordinating electrolytes such as nitrate affords crystalline β-PbO2 with improved charge-transfer resistance (42.6 ± 1.1 Ω), though still poor OER kinetics (134 ± 36 mV dec –1 Tafel slope). By operating amorphous A-PbOx in less coordinating electrolytes, however, a new partially crystalline material can be generated (μc-PbO x ) with further reduced charge-transfer resistance (33.0 ± 1.4 Ω) and improved OER kinetics (70 ± 15 mV dec –1 Tafel slope). The enhanced OER activity of μc-PbO x is the result of coupling the high edge-site population of an amorphous PbOx phase with crystalline-like charge transport properties. Finally, the ability to use an electrolyte to induce OER activity in an inactive amorphous form of PbO x highlights the benefits of optimizing the amorphous–crystalline phase compositions in the design of active OER catalysts.
Toward an international practical pressure scale: A proposal for an IPPS ruby gauge (IPPS-Ruby2020)
At the 26 th AIRAPT conference in 2017, a task group was formed to work on an International Practical Pressure Scale (IPPS). This report summarizes the activities of the task group toward an IPPS ruby gauge. We have selected three different approaches to establishing the relation between pressure ( P ) and ruby R1-line shift ( Δλ ) with three groups of optimal reference materials for applying these approaches. Using a polynomial form of the second order, the recommended ruby gauge (referred as Ruby2020) is expressed by: P [ G P a ] = 1.87 ( ± 0.01 ) × 10 3 Δ λ λ 0 1 + 5.63 ( ± 0.03 ) Δ λ λ 0 , where λ 0 is the wavelength of the R1-line near 694.25 nm at ambient condition. In June of 2020, the Executive Committee of AIRAPT endorsed the proposed Ruby2020. Finally, we encourage high-pressure practitioners to utilize Ruby2020 within its applicable pressure range (up to 150 GPa), so that pressure data can be directly compared across laboratories and amended consistently as better scales emerge in the future.
Design and construction of a new detector to measure ultra-low radioactive-isotope contamination of argon
Large liquid argon detectors offer one of the best avenues for the detection of galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei. The liquid argon target allows exquisite discrimination between nuclear and electron recoil signals via pulse-shape discrimination of the scintillation signals. Atmospheric argon (AAr), however, has a naturally occurring radioactive isotope, 39Ar, a ß emitter of cosmogenic origin. For large detectors, the atmospheric 39Ar activity poses pile-up concerns. The use of argon extracted from underground wells, deprived of 39Ar, is key to the physics potential of these experiments. The DarkSide-20k dark matter search experiment will operate a dual-phase time projection chamber with 50 tonnes of radio-pure underground argon (UAr), that was shown to be depleted of 39Ar with respect to AAr by a factor larger than 1400. Assessing the 39Ar content of the UAr during extraction is crucial for the success of DarkSide-20k, as well as for future experiments of the Global Argon Dark Matter Collaboration (GADMC). This will be carried out by the DArT in ArDM experiment, a small chamber made with extremely radio-pure materials that will be placed at the centre of the ArDM detector, in the Canfranc Underground Laboratory (LSC) in Spain. The ArDM LAr volume acts as an active veto for background radioactivity, mostly ?-rays from the ArDM detector materials and the surrounding rock. This article describes the DArT in ArDM project, including the chamber design and construction, and reviews the background required to achieve the expected performance of the detector.
Effective field theory interactions for liquid argon target in DarkSide-50 experiment
We reanalize data collected with the DarkSide-50 experiment and recently used to set limits on the spin-independent interaction rate of weakly interacting massive particles (WIMPs) on argon nuclei with an effective field theory framework. The dataset corresponds to a total (16660 ± 270) kg d exposure using a target of low-radioactivity argon extracted from underground sources. We obtain upper limits on the effective couplings of the 12 leading operators in the nonrelativistic systematic expansion. For each effective coupling we set constraints on WIMP-nucleon cross sections, setting upper limits between 2.4×10-45 cm2 and 2.3×10-42 cm2 (8.9 ×10-45 cm2 and 6.0 ×10-42 cm2) for WIMPs of mass of 100 GeV/c2 (1000 GeV/c2) at 90% confidence level.
Calibration of the liquid argon ionization response to low energy electronic and nuclear recoils with DarkSide-50
DarkSide-50 has demonstrated the high potential of dual-phase liquid argon time projection chambers in exploring interactions of WIMPs in the GeV=c 2 mass range. The technique, based on the detection of the ionization signal amplified via electroluminescence in the gas phase, allows us to explore recoil energies down to the sub-keV range. We report here on the DarkSide-50 measurement of the ionization yield of electronic recoils down to ~180 eV er , exploiting 37 Ar and 39 Ar decays, and extrapolated to a few ionization electrons with the Thomas-Imel box model. Further, we present a model-dependent determination of the ionization response to nuclear recoils down to ~500 eV nr , the lowest ever achieved in liquid argon, using in situ neutron calibration sources and external datasets from neutron beam experiments.
Application of a headspace GC–MS method to evaluate the product quality of alcohol‐based hand wipe sanitizers
Abstract The investigation of marketed hand wipe sanitizers presented an analytical challenge owing to the need for extraction from the solid matrix of the products. The present work describes the development of a new sample preparation method for the extraction of analytes from the hand wipe sanitizer matrix into dimethyl sulfoxide for analysis using headspace GCMS. Alcohol‐based hand sanitizer (ABHS) wipe products labeled to contain ethanol or isopropanol as active ingredients were tested, varying in the size and weight of the wipes. The spike recovery assay was confirmed using spiking solutions containing impurities at concentrations equivalent to 50, 100 and 200% of the interim concentration limits. All of the tested analytes showed recovery within the allowable limits (80–120%). Six marketed ABHS wipe products were tested and no impurities above the FDA interim limits were observed. One product contained ethanol below the 60% v/v limit and another product was mislabeled for isopropanol and was found to contain ethanol instead. Four of the six ABHS products did not meet the label claim, which may affect the product quality. The analytical method and sample preparation procedures will provide the FDA and ABHS manufacturers with the capability to conduct quality assurance testing of hand wipe sanitizers for active ingredient content and impurities.
Simple Analysis of Primary and Secondary Bile Salt Hydrolysis in Mouse and Human Gut Microbiome Samples by Using Fluorogenic Substrates
Animals produce bile to maximize absorption of lipophilic nutrients in the gut. The physical properties of bile are largely dictated by amphipathic bile salt molecules, which also act as signaling molecules that bind host receptors and modulate physiological processes. Upon excretion of bile salts into the gut, the gut microbiome can create metabolites that have modified signaling capabilities. The category and magnitude of bile salt metabolism can affect the host either positively or negatively. A key modification is bile salt hydrolysis, which is a prerequisite step for all additional microbial modification. Here, we have synthesized five different fluorogenic bile salts that report on hydrolysis activity using a simple, continuous assay. We profile activity in both murine and human fecal samples. Our data demonstrate that most gut microbiomes have the highest capacity for hydrolysis of host-produced bile salts, but some microbially modified bile salts also display significant turnover.
A comparative study on the physicochemical characteristics of nanoparticles released in vivo from CoCrMo tapers and cement–stem interfaces of total hip replacements
The good biocompatibility and corrosion resistance of the bulk CoCrMo alloy has resulted in it being used in the manufacture of implants and load bearing medical devices. These devices, however, can release wear and corrosion products which differ from the composition of the bulk CoCrMo alloy. The physicochemical characteristics of the particles and the associated in vivo reactivity are dictated by the wear mechanisms and electrochemical conditions at the sites of material loss. Debris released from CoCrMo hip bearings, taper junctions, or cement–stem interfaces can, therefore, have different chemical and morphological characteristics, which provide them with different in vivo toxicities. Here, we propose to assess and compare the characteristics of the particles released in vivo from CoCrMo tapers and cement–stem interfaces which have received less attention compared to debris originating from the hip bearings. The study uses state–of–art characterization techniques to provide a detailed understanding of the size, morphology, composition, and chemistry of the particles liberated from the wear and corrosion flakes from revised hip replacements, with an enzymatic treatment. The phase analyses identified Cr 2 O 3 nanoparticles released from tapers and cement–stem interfaces, whose composition did not vary with origin or particle morphology. The size distributions showed significantly smaller particles were released from the stems, compared to the particles originating from the corresponding tapers. Furthermore, the investigation demonstrates that the tribocorrosive processes occurring at the taper and stem interfaces both result in Cr 2 O 3 nanoparticle formation.
Identification and mapping of quantitative trait loci for Fusarium head blight resistance in a synthetic hexaploid × hard red spring wheat population
Abstract Fusarium head blight (FHB), caused byFusarium graminearumSchwabe, is one of the most devastating diseases in wheat (Triticum aestivumL.). The synthetic hexaploid wheat line Largo was developed from a cross between the durum wheat [T. turgidumssp.durum(Desf.) Husn.] variety Langdon and theAegilops tauschiiCosson accession PI 268210, and it was previously found to have a moderate level of FHB resistance. This study was conducted to identify quantitative trait loci (QTL) associated with FHB resistance using a population of 188 recombinant inbred lines (RILs) from a cross between Largo and the susceptible wheat line ND495. The RILs were evaluated for Type II resistance in two greenhouse and two field environments. The disease severity and 90K single‐nucleotide polymorphism marker data were used for QTL analysis, which revealed six QTL on chromosomes 1D, 2D, 5B, and 7D. Four QTL (QFhb.rwg‐1D,QFhb.rwg‐5B,QFhb.rwg‐7D.1, andQFhb.rwg‐7D.3) from Largo had minor effects, whereas two QTL (QFhb.rwg‐2DandQFhb.rwg‐7D.2) from ND495 showed large effects on FHB resistance. The result suggested that ND495 may possess suppressor or susceptibility gene(s) suppressing or masking FHB resistance controlled by the resistance QTL. Among these QTL, four coincided with previously reported QTL, includingFhb9, and two (QFhb.rwg‐1DandQFhb.rwg‐7D.1) are likely novel QTL. From the six QTL regions, 10 Kompetitive allele‐specific PCR markers were developed and validated for marker‐assisted selection. The QTL detected from the resistant and susceptible parents enhance our understanding of FHB resistance expression and provide new resources for improving FHB resistance in wheat.
The SuperCam Instrument Suite on the NASA Mars 2020 Rover: Body Unit and Combined System Tests
The SuperCam instrument suite provides the Mars 2020 rover, Perseverance, with a number of versatile remote-sensing techniques that can be used at long distance as well as within the robotic-arm workspace. These include laser-induced breakdown spectroscopy (LIBS), remote time-resolved Raman and luminescence spectroscopies, and visible and infrared (VISIR; separately referred to as VIS and IR) reflectance spectroscopy. A remote micro-imager (RMI) provides high-resolution color context imaging, and a microphone can be used as a stand-alone tool for environmental studies or to determine physical properties of rocks and soils from shock waves of laser-produced plasmas. SuperCam is built in three parts: The mast unit (MU), consisting of the laser, telescope, RMI, IR spectrometer, and associated electronics, is described in a companion paper. The on-board calibration targets are described in another companion paper. Here we describe SuperCam’s body unit (BU) and testing of the integrated instrument. The BU, mounted inside the rover body, receives light from the MU via a 5.8 m optical fiber. The light is split into three wavelength bands by a demultiplexer, and is routed via fiber bundles to three optical spectrometers, two of which (UV and violet; 245–340 and 385–465 nm) are crossed Czerny-Turner reflection spectrometers, nearly identical to their counterparts on ChemCam. The third is a high-efficiency transmission spectrometer containing an optical intensifier capable of gating exposures to 100 ns or longer, with variable delay times relative to the laser pulse. This spectrometer covers 535–853 nm ( $105\text{--}7070~\text{cm}^{-1}$ Raman shift relative to the 532 nm green laser beam) with $12~\text{cm}^{-1}$ full-width at half-maximum peak resolution in the Raman fingerprint region. The BU electronics boards interface with the rover and control the instrument, returning data to the rover. Thermal systems maintain a warm temperature during cruise to Mars to avoid contamination on the optics, and cool the detectors during operations on Mars.Results obtained with the integrated instrument demonstrate its capabilities for LIBS, for which a library of 332 standards was developed. Examples of Raman and VISIR spectroscopy are shown, demonstrating clear mineral identification with both techniques. Luminescence spectra demonstrate the utility of having both spectral and temporal dimensions. Finally, RMI and microphone tests on the rover demonstrate the capabilities of these subsystems as well.
Zeolite supported Pd catalysts for the complete oxidation of methane: A critical review
This review summarizes the recent literature reports on the development of zeolite supported Pd catalysts for the complete oxidation of methane. In-depth analysis reveals that different types of zeolite framework structures, regardless of the dimensionality, pore opening structure, and channel size, have little influence on the methane oxidation activity or the on-stream stability of the supported Pd catalysts. In contrast, the Si/Al ratio of a zeolite support plays a critical role. Both the catalytic activity and the on-stream stability of a Pd/zeolite catalyst increase with the increase of the Si/Al ratio. Catalysts supported on siliceous zeolites consistently show excellent light-off activity and remarkable on-stream stability whether in a dry or wet feed. Silanol nest defect sites in a siliceous zeolite are proposed to be the anchoring sites promoting the formation and minimizing the sintering of finely dispersed Pd nanoparticles. Remaining challenges in overcoming the sulfur poisoning effect are discussed.
A study of events with photoelectric emission in the DarkSide-50 liquid argon Time Projection Chamber
Finding unequivocal evidence of dark matter interactions in a particle detector is a major goal of research in physics. Liquid argon time projection chambers offer a path to probe Weakly Interacting Massive Particles scattering cross sections on nuclei down to the so-called neutrino floor, in a mass range from a few GeV to hundreds of TeV. Based on the successful operation of the DarkSide-50 detector at LNGS, a new and more sensitive experiment, DarkSide-20k, has been designed and is now under construction. A thorough understanding of the DarkSide-50 detector response and, therefore, of all types of events observed in the detector, is essential for the optimal design of the new experiment. In this article, we report on a specific set of events, namely, standard two-pulse scintillation–ionization signals with a third small amplitude pulse, occurring within the 440 μ s data acquisition window of standard events. Some of these events are due to the photoionization of the TPC cathode. We compare our results with those published by collaborations using liquid xenon time projection chambers, which observed a similar phenomenon, and, in particular, with a recent paper by the LUX Collaboration (D.S. Akerib et al. Phys.Rev.D 102, 092004 (2020)) From the measured rate of these events, we estimate for the first time the quantum efficiency of the tetraphenyl butadiene deposited on the DarkSide-50 cathode at wavelengths of around 128 nm, in liquid argon. Also, both experiments observe events likely related to the photoionization of impurities in the liquid. The probability of photoelectron emission per unit length turns out to be an order of magnitude lower in DarkSide-50 than in LUX.
Study of cosmogenic activation above ground for the DarkSide-20k experiment
The activation of materials due to exposure to cosmic rays may become an important background source for experiments investigating rare event phenomena. DarkSide-20k, currently under construction at the Laboratori Nazionali del Gran Sasso, is a direct detection experiment for galactic dark matter particles, using a two-phase liquid-argon Time Projection Chamber (TPC) filled with 49.7 tonnes (active mass) of Underground Argon (UAr) depleted in 39 Ar. Despite the outstanding capability of discriminating γ / β background in argon TPCs, this background must be considered because of induced dead time or accidental coincidences mimicking dark-matter signals and it is relevant for low-threshold electron-counting measurements. Here, the cosmogenic activity of relevant long-lived radioisotopes induced in the experiment has been estimated to set requirements and procedures during preparation of the experiment and to check that it is not dominant over primordial radioactivity; particular attention has been paid to the activation of the 120 t of UAr used in DarkSide-20k. Expected exposures above ground and production rates, either measured or calculated, have been considered in detail. From the simulated counting rates in the detector due to cosmogenic isotopes, it is concluded that activation in copper and stainless steel is not problematic. The activity of 39 Ar induced during extraction, purification and transport on surface is evaluated to be 2.8% of the activity measured in UAr by DarkSide-50 experiment, which used the same underground source, and thus considered acceptable. Other isotopes in the UAr such as 37 Ar and 3 H are shown not to be relevant due to short half-life and assumed purification methods.
Energy catalysis needs ligands with high oxidative stability
Replacing fossil fuel-based energy by renewable sources is a transition that society needs to make to meet future energy demand and simultaneously address climate change. Coupling renewable energy sources with electrochemical catalysis provides a promising path to carbon-neutral fuels and chemicals when the necessary reducing equivalents and protons are harvested from water. Developing highly active, stable, and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is accordingly a centerpiece of a renewable energy portfolio. Whereas viable OER catalysts are heterogeneous in nature, owing to their oxidative stability, the realization of stable molecular OER catalysts greatly expands the horizon of energy science with the ability to tune OER energetics and mechanisms with fidelity. In this perspective, current challenges in the field of molecular OER catalysis are addressed with promising lines of research that are directed to designing ligands that can withstand the harsh oxidizing environment of OER.
A finite difference informed random walker (FDiRW) solver for strongly inhomogeneous diffusion problems
In nature, many complex multi-physics coupling problems exhibit strong diffusivity inhomogeneity. For instance, in the context of radionuclide absorption by porous wasteform materials within a flowing waste stream, the difference of species’ diffusivity in solid and liquid phases spans by 3~8 orders of magnitude. To solve the diffusion equations with strongly inhomogeneous diffusivity, traditional discretization-based methods, such as the Finite Difference Method (FDM), require infinitesimally small time steps (<10 -10 ) as high spatial resolutions are employed in most microstructure evolution processes, leading to prohibitively high computational costs. Here, this work developed an integrated numerical approach (FDiRW: Finite Difference informed Random Walk) to tackle this challenge. The idea is that utilizing the Random Walk concept, the fast diffusion is modeled as a superposition of point source’s solution for a concentration distribution while FDM is used to obtain the point source’s solution at each node. A mesh-coarsening algorithm is developed to generate an exclusive coarse mesh for FDiRW approach to maximize its efficiency. The effectiveness of the coarse mesh-based FDiRW approach is validated by benchmarking Finite Difference solutions. Numerical results demonstrated that FDiRW achieves a remarkable 1000x computational efficiency improvement over FDM while preserving desired accuracy for a medium-sized model of 192 × 192 × 192 grids. Finally, as models scale up, a floating-point operations (PLOPs) analysis of the FDiRW algorithm reveals that its computational complexity grows quadratically in terms of the number of nodes employed in computation.