Iridium-based catalysts remain the most reliable option for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWEs). However, their high cost and limited performance represent critical barriers to the commercialization of this green hydrogen production technology. Herein, we report the creation of a metallic Ir nanowire network (IrNWN), which exhibits superior OER performance through its in situ transition into an oxide structure with high intrinsic activity. At a low loading of 0.25 mgIr/cm2 in PEMWEs, IrNWN achieved a current density of 3.13 A/cm2 at a cell voltage of 1.8 V, outperforming the commercial Ir-based catalyst and surpassing the Department of Energy (DOE) 2026 technical target. Moreover, the high activity of IrNWN was maintained for 900 h in a durability test at 2 A/cm2, showing a low degradation rate of 0.042 mV/hour. Structural analysis of the electrochemically oxidized IrNWN revealed the presence of mixed Ir oxidation states and a high density of surface terminal oxygen groups (µ1-O), which contributed to a reduced energy barrier for the rate-determining O-O coupling step.

Metal-arene sandwich complexes are foundational to organometallic chemistry, yet analogous compounds of the f-elements remain rare, especially for the actinides. This scarcity has limited efforts to understand how this iconic metal-arene bonding motif changes when extended to actinide elements, where metal-carbon bonding, charge transfer, and ligand redox behaviour may depart from established d-block patterns. Here we report the first homoleptic tris(arenide) arenocenes of the felements, together with a related heteroleptic uranium arenocene, establishing a new class of actinide sandwich compounds supported by formally dianionic arene ligands. Crystallographic, spectroscopic, magnetic, X-ray absorption, and multireference computational analyses support their formulation as tetravalent uranium centres engaged in appreciable arene-to-uranium π-bonding interactions across varying coordination modes. The overall metal contribution to bonding decreases as the arene πsystem expands, while 5f-orbital participation becomes more pronounced in complexes bearing larger arene ligands. Direct comparison with the structurally related d-block complex [Hf(η4-C10H8)3]2− reveals greater orbital participation in the uranium system, providing comparative measure for 5f engagement in metal-arene interactions and establishing a new platform for investigating actinide valence orbital contributions to bonding.

To facilitate X-ray absorption spectroscopy (XAS) measurements of air-sensitive samples, we present a simple method in which materials are encased in common paraffin wax to protect them from air and moisture. We demonstrate the efficacy of this approach using a highly reducing, air- and moisture-sensitive uranium(iii) complex, the tris(amide) U[N(SiMe3)2]3 (1). When finely dispersed in a boron nitride matrix and subsequently encased in inert paraffin wax, samples of 1 remain stable with no visible or spectroscopic degradation after several days under ambient conditions. The viability of this method for XAS measurements was further evaluated across a series of uranium compounds, ranging from uranyl species to highly air- and moisture-sensitive molecular complexes, at the uranium L3-edge. Edge energy determinations were highly reproducible (+/- 0.1 eV between replicates) and, where available, showed excellent agreement with literature values. This low-cost, effective, and versatile method offers a viable solution for XAS studies of air-sensitive compounds and materials.

All-solid-state batteries hold greater promise for improving safety and energy density over conventional battery technology employing organic liquid electrolytes. One of the required features of a Li+ conducting solid electrolyte is electrochemical stability, attained thermodynamically or kinetically, within the targeted operating voltage and temperature ranges. Therefore, understanding of the oxidative or reductive degradation mechanism is important to allow the design of stable solid electrolyte materials. This work contributes to building an understanding of the oxidative degradation mechanism in lithium solid electrolytes at cell operating conditions. Here, we have focused on resolving the oxidative decomposition mechanism of Al-doped lithium garnet Li6.28Al0.24La3Zr2O12 (LLZO) as a state-of-the-art inorganic ceramic electrolyte. By combining experimental and computational analyses, we show that oxidation of LLZO occurs by simultaneous loss of oxygen and lithium from the structure, resulting in substoichiometric LLZO, at a moderate temperature (80 degrees C) and a high electrode potential (4.3 V vs Li/Li+). Based on X-ray absorption and diffraction analyses, we find that the zirconium coordination shells in LLZO contract while the crystal structure experiences positive chemical strain upon electrochemical oxidation. The results from ex situ structural characterization of both the local structure and crystal symmetry are supported by a substoichiometric LLZO with lithium and oxygen vacancies, modeled by density functional theory (DFT) calculations. These chemical and structural changes in LLZO suppress effective lithium-ion conductivity by an order of magnitude. Formation of lithium and oxygen vacancies in LLZO upon electrochemical oxidation is different from prior thermodynamic predictions of phase decomposition of LLZO. The difference here is that the experiments were conducted at near-room temperature, which can hinder the kinetics of phase separation, and thus, the resultant LLZO solid electrolyte is still single-phase but substoichiometric in Li and O. These findings contribute an important degradation mechanism of the electrolyte, relevant for practical operational conditions of solid-state batteries.

High entropy oxides (HEOs) have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)(0.167)(MnCr)(0.083)O, a composition based on the parent HEO (MgNiCuCoZn)(0.2)O. We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X-ray diffraction shows lattice parameters to decrease with increased pO(2) pressures until the onset of phase separation. X-ray absorption fine structure shows that specific atomic species in the composition dictate the global structure of the material as Cr, Co, and Mn shift to energetically favorable coordination with increasing pressure. Transmission electron microscopy analysis on a lower-pressure sample exhibits a rock salt structure, but the higher-pressure sample reveals reflections reminiscent of the spinel structure. In all, these findings give a more complete picture of how (MgNiCuCoZn)(0.167)(MnCr)(0.083)O forms with varying initial conditions and advances fundamental knowledge of cation behavior in high entropy oxides.

There is an urgent need for highly efficient sorbents capable of selectively removing 99TcO4- from concentrated alkaline nuclear wastes, which has long been a significant challenge. In this study, we present the design and synthesis of a high-performance adsorbent, CPN-3 (CPN denotes cationic polymeric nanotrap), which achieves excellent 99TcO4- capture under strong alkaline conditions by incorporating branched alkyl chains on the N3 position of imidazolium units and optimizing the framework anion density within the pores of a cationic polymeric nanotrap. CPN-3 features exceptional stability in harsh alkaline and radioactive environments as well as exhibits fast kinetics, high adsorption capacity, and outstanding selectivity with full reusability and great potential for the cost-effective removal of 99TcO4-/ReO4- from contaminated water. Notably, CPN-3 marks a record-high adsorption capacity of 1052 mg/g for ReO4- after treatment with 1 M NaOH aqueous solutions for 24 h and demonstrates a rapid removal rate for 99TcO4- from simulated Hanford and Savannah River Site waste streams. The mechanisms for the superior alkaline stability and 99TcO4- capture performances of CPN-3 are investigated through combined experimental and computational studies. This work suggests an alternative perspective for designing functional materials to address nuclear waste management.

Catalytic is a crucial reaction for environmental detoxication of pesticides and neutralization of various molecules classified as chemical warfare agents. Herein, we report on a series of tunable Ce-Zr-based metal oxides, (ZraCe1-aOx) prepared using a facile biomineralization technique, as catalysts for organophosphates dephosphorylation. Synchrotron scattering and spectroscopy methods showcase that ZraCe1-aOx catalysts are highly defective and exhibit an abundance of Ce3+ sites that promote oxygen vacancies needed for enhanced dephosphorylation reactions. The catalytic performance was assessed using a model para-nitrophenyl phosphate reaction and showcases a strong dependence on Zr dopant concentration and subsequent tuning of the Ce3+/Ce4+ ratio. Analysis of synchrotron datasets allowed structure-performance correlations between the Ce3+ concentration and associated oxygen vacancies, the dephosphorylation rate constant, and Zr concentration to be established, confirming that Ce3+ as active sites is positively correlated with the rate constant. We envision that similar biomineralization approaches can be used to fabricate Ce3+-rich Ce-Zr oxide for environmental application in dephosphorylation and other hydrolysis reactions.

Chalcogen environments tend to stabilize low oxidation states, thus making the +5 oxidation state in uranium chalcogenides extremely rare. Having one unpaired electron, the magnetism of U+5, 5f(1), is of significant interest; however, it is underexplored due to a scarcity of examples. Three related all-U+5 chalcogenides, Na2Cu5US6, Na3Cu4US6, and Na3Cu4USe6, were obtained as single crystals via the flux-assisted boron chalcogen mixture method as part of a broader investigation of the Na-Cu-U-Q (Q = S and Se) systems. To test the formation of the Se-analog of Na2Cu5US6, we performed in situ high-temperature powder X-ray diffraction using sealed capillaries; this approach demonstrated the formation and presence of only Na3Cu4USe6 and not "Na2Cu5US6" in the reaction mixture. In addition to assigning oxidation states using charge balance and the sample composition, oxidation states of copper, +1, and uranium, +5, in Na2Cu5US6 were also determined via X-ray absorption near edge spectroscopy. Magnetic properties were investigated on both bulk powder samples of Na2Cu5US6 and Na(3)Cu(4)UQ(6) (Q = S and Se) and millimeter-size single crystals of Na2Cu5US6, where magnetic susceptibility and magnetization vs field measurements revealed antiferromagnetic behavior of Na2Cu5US6 and Na(3)Cu(4)UQ(6) (Q = S and Se) with a T N of 4.7, 3.4, and 5.9 K, respectively. Finally, a broad discussion of the effective magnetic moment of U+5, which is significantly smaller, 1.06 mu B in Na2Cu5US6 and 1.08 mu B in Na(3)Cu(4)UQ(6), than predicted by spin-only (1.73 mu B) and total angular momentum (2.54 mu B) models. The fact that only about 20 compositions of such materials are currently known, highlights the need to explore additional compositions containing uranium in rare oxidation states before it will be possible to understand the magnetic properties of such materials more fully.

Metal-organic frameworks (MOFs) show remarkable potential in a broad array of applications given their physical and chemical versatility. Classical synthesis of MOFs is performed using solution chemistry at elevated temperatures to achieve reversible metal-ligand bond formation. These harsh conditions may not be suitable for chemical species sensitive to high temperature or prone to deleterious reactions with solvents. For instance, Pd(ii) is susceptible to reduction under solvothermal conditions and is not a common metal node of MOFs. We report a generic and facile mechanochemical strategy that directly incorporates a series of Pd(ii)-based heterobimetallic clusters into MOFs as metal nodes without Pd(ii) being reduced to Pd(0). Mechanochemistry features advantages of short reaction time, minimum solvent, high reaction yield, and high degree of synthetic control. Catalytic performances of lattice-confined heterobimetallic sites are examined for nitrene transfer reactions and we demonstrate that the chemoselectivity for allylic amination versus olefin aziridination is readily tuned by the identity of the first-row metal ion in Pd(ii)-based heterobimetallic clusters.

The study of high-entropy materials has attracted enormous interest since they could show new functional properties that are not observed in their related parent phases. Here, we report single crystal growth, structure, thermal transport, and magnetic property studies on a novel high-entropy oxide with the spinel structure (MgMnFeCoNi)Al2O4. We have successfully grown high-quality single crystals of this high-entropy oxide using the optical floating zone growth technique for the first time. The sample was confirmed to be a phase pure high-entropy oxide using x-ray diffraction and energy-dispersive spectroscopy. Through magnetization measurements, we found (MgMnFeCoNi)Al2O4 exhibits a cluster spin glass state, though the parent phases show either antiferromagnetic ordering or spin glass states. Furthermore, we also found that (MgMnFeCoNi)Al2O4 has much greater thermal expansion than its CoAl2O4 parent compound using high resolution neutron Larmor diffraction. We further investigated the structure of this high-entropy material via Raman spectroscopy and extended x-ray absorption fine structure spectroscopy (EXAFS) measurements. From Raman spectroscopy measurements, we observed (MgMnFeCoNi)Al2O4 to display a combination of the active Raman modes in its parent compounds with the modes shifted and significantly broadened. This result, together with the varying bond lengths probed by EXAFS, reveals severe local lattice distortions in this high-entropy phase. Additionally, we found a substantial decrease in thermal conductivity and suppression of the low temperature thermal conductivity peak in (MgMnFeCoNi)Al2O4, consistent with the increased lattice defects and strain. These findings advance the understanding of the dependence of thermal expansion and transport on the lattice distortions in high-entropy materials.

The recent breakthrough in confining five or more atomic species in nanocatalysts, referred to as high-entropy alloy nanocatalysts (HEAs), has revealed the possibilities of multielemental interactions that can surpass the limitations of binary and ternary electrocatalysts. The wide range of potential surface configurations in HEAs, however, presents a significant challenge in resolving active structural motifs, preventing the establishment of structure-function relationships for rational catalyst design and optimization. We present a methodology for creating sub-5 nm HEAs using an aqueous-based peptide-directed route. Using a combination of pair distribution function and X-ray absorption spectroscopy, HEA structure models are constructed from reverse Monte Carlo modeling of experimental data sets and showcase a clear peptide-induced influence on atomic-structure and chemical miscibility. Coordination analysis of our structure models facilitated the construction of structure-function correlations applied to electrochemical methanol oxidation reactions, revealing the complex interplay between multiple metals that leads to improved catalytic properties. Our results showcase a viable strategy for elucidating structure-function relationships in HEAs, prospectively providing a pathway for future materials design.

Selective uranium extraction from seawater by dopant engineered layered double hydroxide.

Relationship between d-metal active species (Co, Ni, & Cu) in Prussian blue analogue derived metal oxide/hydroxide films and the activation energy needed for full conversion of 5-HMF to 2,5-FDCA in alkaline solution.

In uranium endohedral metallofullerenes, cage isomer dependent oxidation states have been theoretically deter-mined for U3+@C2v(9)-C823- and U4+@C2(5)-C824+. Solution phase EPR supports this assessment; however, in the solid-state, EPR, SQUID magnetometry, and XANES suggest both isomers adopt a common metal-oxidation state. This inves-tigation shows the redox active uranium center may be sensitive to changes at the carbon cage, demonstrating that solution versus solid-state factors is a possible consideration when determining the electronic structure and reactivity of these unique systems.

Atomically dispersed heteroatom coordinated metal sites (ADMS) have been recognized as promising candidates for electrochemical conversion. Among a diverse range of molecular precursors for ADMS synthesis, framework materials are particularly interesting due to the presence of pre-formed heteroatoms coordinated active sites. Herein, we demonstrate that the copper boron imidazolate cage, BIF-29(Cu) can be an ideal precursor for nitrogen coordinated single site Cu catalyst for electrocatalytic carbon dioxide reduction (CO 2 RR). Although the pristine material exhibited moderate methane selectivity over hydrogen evolution reaction (HER), the methane selectivity is significantly enhanced by 2 times (55 % CH 4 at -1.25 V vs. RHE) after mild thermal activation. Extensive characterization methods indicate the transformation of crystalline BIF-29(Cu) into an amorphous carbonaceous material comprising isolated CuN x sites. Moreover, in situ X-ray absorbance spectroscopy further indicates stable CuN x sites that are reduced during CO 2 RR. This work encourages the discovery of single-site electrocatalytic systems through a rational selection of molecular precursor and calcination parameters for promoting electrocatalytic selectivity. atomically dispersed metal sites, conversion, situ observed catalytic enhancement in the BIF-29(Cu)-200C. work demonstrates the potential of coordination cage materials for the synthesis of single-site metal catalysts and avails new opportunities for rational materials design. was performed before the electrolysis to measure the solution resistance. At 10 4 Hz, the real component of the Nyquist plot was used as solution resistance and 85 % of that resistance was compensated using the software. The remaining 15 % resistance was compensated manually after electrolysis. Electrolysis experiments at each potential were repeated at least 3 times with separately prepared electrodes and the average and standard deviation are shown.

An unprecedented sandwich complex of the actinides is synthesized from the treatment of [UI2(HMPA)4]I (HMPA = OP(NMe2)3) (2) with 3 equiv. of K(C14H10) to give the neutral, bis(arenide) species U(η6-C14H10)(η4-C14H10)(HMPA)2 (1). Solid-state X-ray, SQUID magnetometry, and XANES analyses are consistent with tetravalent uranium supported by [C14H10]2- ligands. In one case, treatment of 1 with an equiv. of AgOTf led to the isolation of U(η6-C14H10)2(HMPA)(THF) (3), formed from ring migration and haptotropic rearrangement. Complete active space (CASSCF) calculations indicate the U-C bonding to solely consist of π-interactions, presenting a unique electronic structure distinct from classic actinide sandwich compounds.

Carbon electrodes chemically modified with molecular active sites are potent catalysts for key energy conversion reactions. Generally, it is assumed that these molecularly modified electrodes operate by the same redox mediation mechanisms observed for soluble molecules, in which electron transfer and substrate activation occur in separate elementary steps. Here, we uncover that, depending on the solvent, carbon-bound cobalt porphyrin can carry out electrolysis by the non-mediated mechanisms of metal surfaces in which electron transfer and substrate activation are concerted. We chemically modify glassy carbon electrodes with cobalt tetraphenylporphyrin units that are anchored by flexible aliphatic linkages to form CH-CoTPP. In acetonitrile, CH-CoTPP displays a clear outer-sphere Co(II/I) process which catalyzes the H2 evolution reaction by a step-wise, redox-mediated reaction sequence. In contrast, clear surface redox waves are not observed for CH-CoTPP in aqueous media and H2 evolution proceeds via a non-mediated, concerted proton-electron transfer reaction sequence over a wide pH range. The data suggest that, in aqueous electrolyte, the CoTPP fragments reside inside the electrochemical double layer and are electrostatically coupled to the surface. This coupling allows CH-CoTPP to carry out catalysis without being pinned to the redox potential of the molecular fragment. These studies highlight that the simple adsorption of molecules can lead to reaction mechanisms typically reserved for metal surfaces, ex-posing new principles for the design of molecularly-modified electrodes.

Bacterial reduction of Se(IV) is a significant component of the global selenium cycle, and hence affects the fate and transport of selenium in both natural and contaminated environments. However, it is unknown whether bacterially-produced exudates are capable of reducing selenium independent of bacterial cells. In this study, we measured the rate and extent of Se(IV) reduction by exudates from three bacterial species, and we determined the importance of exudate sulfhydryl sites by conducting parallel experiments after treatment of the exudates with a sulfhydryl-specific blocking molecule. We also conducted experiments with whole cell biomass for each of the three bacterial species to determine the importance of exudate-only reduction relative to whole biomass-promoted reduction. Under our experimental conditions, exudates from Bacillus subtilis and Pseudomonas putida remove Se(IV) from solution after an approximately 20-24 h lag period, but exudates from Shewanella oneidensis are ineffective at Se(IV) removal, except when the cells are grown in the presence of Se(IV). For both B. subtilis and P. putida, pretreatment blocking of the sulfhydryl sites on the exudate molecules dramatically decreases the rate and extent of Se (IV) removal, strongly suggesting that sulfhydryl groups on the exudate molecules play a key role in the Se(IV) reduction mechanism. The behavior of S. oneidensis exudates indicates that up-regulation of the Se (IV) reduction mechanism can occur in response to the Se content of the medium in which the cells grow. Our results demonstrate the capacity of some bacterial exudates to reduce Se(IV), and suggest that the activity of bacterial exudates should be accounted for when modeling selenium cycling in natural and engineered environments. (C) 2022 Published by Elsevier Ltd.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The electrocatalytic CO2 RR to produce value-added chemicals and fuels has been recognized as a promising means to reduce the reliance on fossil resources; it is, however, hindered due to the lack of high-performance electrocatalysts. The effectiveness of sculpturing metal/metal oxides (MMO) heterostructures to enhance electrocatalytic performance toward CO2 RR has been well documented, nonetheless, the precise synergistic mechanism of MMO remains elusive. Herein, an in operando electrochemically synthesized Cr2 O3 -Ag heterostructure electrocatalyst (Cr2 O3 @Ag) is reported for efficient electrocatalytic reduction of CO2 to CO. The obtained Cr2 O3 @Ag can readily achieve a superb FECO of 99.6% at -0.8 V (vs RHE) with a high JCO of 19.0 mA cm-2 . These studies also confirm that the operando synthesized Cr2 O3 @Ag possesses high operational stability. Notably, operando Raman spectroscopy studies reveal that the markedly enhanced performance is attributable to the synergistic Cr2 O3 -Ag heterostructure induced stabilization of CO2 •- /*COOH intermediates. DFT calculations unveil that the metallic-Ag-catalyzed CO2 reduction to CO requires a 1.45 eV energy input to proceed, which is 0.93 eV higher than that of the MMO-structured Cr2 O3 @Ag. The exemplified approaches in this work would be adoptable for design and development of high-performance electrocatalysts for other important reactions.