Deforming lanthanum trihydride for superionic conduction.

With strong reducibility and high redox potential, the hydride ion (H-) is a reactive hydrogen species and an energy carrier. Materials that conduct pure H- at ambient conditions will be enablers of advanced clean energy storage and electrochemical conversion technologies1,2. However, rare earth trihydrides, known for fast H migration, also exhibit detrimental electronic conductivity3-5. Here we show that by creating nanosized grains and defects in the lattice, the electronic conductivity of LaHx can be suppressed by more than five orders of magnitude. This transforms LaHx to a superionic conductor at -40 °C with a record high H- conductivity of 1.0 × 10-2 S cm-1 and a low diffusion barrier of 0.12 eV. A room-temperature all-solid-state hydride cell is demonstrated.

Spontaneous Reconstruction of Copper Active Sites during the Alkaline CORR: Degradation and Recovery of the Performance.

Understanding the reconstruction of electrocatalysts under operational conditions is essential for studying their catalytic mechanisms and industrial applications. Herein, using spatiotemporally resolved Raman spectroscopy with CO as a probe molecule, we resolved the spontaneous reconstruction of Cu active sites during cathodic CO reduction reactions (CORRs). Quasi-in situ focused ion beam transmission electron microscopy (FIB-TEM) revealed that under prolonged electrolysis, the Cu surface can reconstruct to form nanometer-sized Cu particles with (111)/(100) facets and abundant grain boundaries, which strongly favor the formation of an inactive *CObridge binding site and deteriorate the CORR performance. A short period of anodic oxidation can efficiently remove these reconstructed nanoparticles by quick dissolution of Cu, thus providing an effective strategy to regenerate the Cu catalysts and recover their CORR performance. This study provides real-time in situ observations of Cu reconstruction and changes in the binding of key reaction intermediates, highlighting the decisive role of the local active site, rather than the macroscopic morphology, on adsorption of key reaction intermediates and thus CORR performance.

One-Step Synthesis of Light Metal Nanoparticle from Metastable Complex.

Metal nanoparticles have attracted considerable scientific and technological interest in recent years, most related explorations and reports are focused on transition and noble metals. However, the synthesis and application of light metal nanoparticles represented by Mg have not been fully exploited, limited by their ultrahigh reactivity in air and preparation in harsh conditions. In this work, a simple and effective one-step organic solvent-assisted ball-milling process is developed to synthesize Mg and Li nanoparticles, which permits the formation of MgH2 in a hydrogen atmosphere in a one-step reaction process at ambient temperature. Further studies suggest that acetone chemisorbs on defects/surfaces of Mg during ball milling leading to the formation of a metastable magnesium complex, which significantly alters the physical and chemical characteristics of Mg grains. The formation of metastable complexes provides an attractive strategy to produce light metal nanoparticles and inspires the authors to study the interaction of organic solvents with light metals.

CuCeOx/CuO Catalyst Derived from the Layered Double Hydroxide Precursor: Catalytic Performance in NO Reduction with CO in the Presence of Water and Oxygen.

Valencies of metal species and lattice defects, such as oxygen vacancies, play a pivotal role in metal oxide-catalyzed reactions. Herein, we report a promising synthetic strategy for preparing CuO-supported CuCeOx catalysts (CuCeOx/CuO) by calcination of a hydrotalcite precursor [Cu6Ce2(OH)16]CO3·nH2O. The structural and chemical properties of catalysts were characterized by XRD, ICP-AES, TEM, TPR, NH3-TPD, XPS, Raman spectroscopy, and N2 adsorption, which revealed that the thermal pretreatment in an oxidative atmosphere caused segregation and reconstitution processes of the precursor, resulting in a mesoporous catalyst consisting of well-dispersed CuO-supported CuCeOx clusters of 1.8-3.2 nm in size with a high population of oxygen vacancies. The as-prepared catalyst shows excellent catalytic performance in the reduction of NO by CO in the absence as well as in the presence of water and oxygen. This behavior is attributed to its high oxygen defect concentration facilitating the interplay of the redox equilibria between Cu2+ and reduced copper species (Cu+/Cu0) and (Ce4+/Ce3+). The high surface population of oxygen vacancies and in situ-generated metallic copper species have been evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. The layered double hydroxide-derived CuCeOx/CuO also showed good water tolerance and long-term stability. In situ infrared spectroscopy investigations indicated that adsorbed hyponitrite species are the main reaction intermediates of the NO conversion as also corroborated by theoretical simulations.

Atomic Insight into the Local Structure and Microenvironment of Isolated Co-Motifs in MFI Zeolite Frameworks for Propane Dehydrogenation.

Embedding metal species into zeolite frameworks can create framework-bond metal sites in a confined microenvironment. The metals sitting in the specific T sites of zeolites and their crystalline surroundings are both committed to the interaction with the reactant, participation in the activation, and transient state achievement during the whole catalytic process. Herein, we construct isolated Co-motifs into purely siliceous MFI zeolite frameworks (Co-MFI) and reveal the location and microenvironment of the isolated Co active center in the MFI zeolite framework particularly beneficial for propane dehydrogenation (PDH). The isolated Co-motif with the distorted tetrahedral structure ({(≡SiO)2Co(HO-Si≡)2}, two Co-O-Si bonds, and two pseudobridging hydroxyls (Co···OH-Si) is located at T1(7) and T3(9) sites of the MFI zeolite. DFT calculations and deuterium-labeling reactions verify that the isolated Co-motif together with the MFI microenvironment collectively promotes the PDH reaction by providing an exclusive microenvironment to preactivate C3H8, polarizing the oxygen in Co-O-Si bonds to accept H* ({(≡SiO)CoHδ- (Hδ+O-Si≡)3}), and a scaffold structure to stabilize the C3H7* intermediate. The Co-motif active center in Co-MFI goes through the dynamic evolutions and restoration in electronic states and coordination states in a continuous and repetitive way, which meets the requirements from the series of elementary steps in the PDH catalytic cycle and fulfills the successful catalysis like enzyme catalysis.

Potential-Driven Restructuring of Cu Single Atoms to Nanoparticles for Boosting the Electrochemical Reduction of Nitrate to Ammonia.

Restructuring is ubiquitous in thermocatalysis and of pivotal importance to identify the real active site, yet it is less explored in electrocatalysis. Herein, by using operando X-ray absorption spectroscopy in conjunction with advanced electron microscopy, we reveal the restructuring of the as-synthesized Cu-N4 single-atom site to the nanoparticles of ∼5 nm during the electrochemical reduction of nitrate to ammonia, a green ammonia production route upon combined with the plasma-assisted oxidation of nitrogen. The reduction of Cu2+ to Cu+ and Cu0 and the subsequent aggregation of Cu0 single atoms is found to occur concurrently with the enhancement of the NH3 production rate, both of them are driven by the applied potential switching from 0.00 to -1.00 V versus RHE. The maximum production rate of ammonia reaches 4.5 mg cm-2 h-1 (12.5 molNH3 gCu-1 h-1) with a Faradaic efficiency of 84.7% at -1.00 V versus RHE, outperforming most of the other Cu catalysts reported previously. After electrolysis, the aggregated Cu nanoparticles are reversibly disintegrated into single atoms and then restored to the Cu-N4 structure upon being exposed to an ambient atmosphere, which masks the potential-induced restructuring during the reaction. The synchronous changes of the Cu0 percentage and the ammonia Faradaic efficiency with the applied potential suggests that the Cu nanoparticles are the genuine active sites for nitrate reduction to ammonia, which is corroborated with both the post-deposited Cu NP catalyst and density functional theory calculations.

Switchable Tuning CO2 Hydrogenation Selectivity by Encapsulation of the Rh Nanoparticles While Exposing Single Atoms.

The switch of CO2 hydrogenation selectivity from CH4 to CO over TiO2 supported Rh catalysts is accomplished via selective encapsulation of Rh nanoparticles while exposing Rh single atoms by high-temperature reduction (HTR) according to their different strong metal-support interaction (SMSI) occurrence conditions, which can be reversed by subsequent oxidation treatment.

Synthesis of Nickel Nitride-Based 1D/0D Heterostructure via a Morphology-Inherited Nitridation Strategy for Efficient Electrocatalytic Hydrogen Evolution.

The fabrication of heterostructures has inspired extensive interest in promoting the performance of solar cells or solar fuel production, but it is still challenging for nitrides to prepare structurally ordered heterostructures. Herein, one nickel nitride-based heterostructure composed of 1D Ni0.2 Mo0.8 N nanorods and 0D Ni3 N nanoparticles (denoted as NiMoN/NiN) is reported to exhibit significantly promoted hydrogen evolution reaction performance in both alkaline and neutral media. In particular, the optimal overpotential of the NiMoN/NiN sample at 10 mA cm-2 in 1 m KOH is 49 mV. The successful fabrication of 1D/0D heterostructures is mainly ascribed to morphology-inherited nitridation of 1D oxide precursor (denoted as NiMoO-NRs) in situ grown on Ni foam surface, and attributed to strong Lewis acid-base interaction that renders the Ni2+ ions emitted from the oxide precursor to well coordinate with NH3 for the formation of Ni3 N nanoparticles during the nitridation process. It is theoretically and experimentally demonstrated that the special 1D/0D heterostructure provides tandem active phases Ni0.2 Mo0.8 N and Ni3 N for synergistic promotion in lowering the activation energy of H2 O dissociation and optimizing the adsorption energy of H, respectively. This work may open a new avenue for developing highly active tandem electrocatalysts for promising renewable energy conversion.

Enhancement of Mass Transport for Oxygen Reduction Reaction Using Petal-Like Porous Fe-NC Nanosheet.

Nitrogen-coordinated single-atom catalysts (SACs) have emerged as a new frontier for accelerating oxygen reduction reaction (ORR) owing to the optimal atom efficiency and fascinating properties. However, augmenting the full exposure of active sites is a crucial challenge in terms of simultaneously pursuing high metal loading of SACs. Here, petal-like porous carbon nanosheets with densely accessible Fe-N4 moieties (FeNC-D) are constructed by combining the space-confinement of silica and the coordination of diethylenetriaminepentaacetic acid. The resulted FeNC-D catalyst possesses an enhanced mesoporosity and a balanced hydrophobicity/hydrophilicity, which can facilitate mass transport and advance the exposure of inaccessible Fe-N4 sites, resulting in efficient utilization of active sites. By virtue of the petal-like porous architecture with maximized active site density, FeNC-D demonstrates superior ORR performance in a broad pH range. Remarkably, when utilized as the air cathode in Zn-air battery (ZAB) and microbial fuel cell (MFC), the FeNC-D-based device displays a large power density (356 mW cm-2 for ZAB and 1041.3 mW m-2 for MFC) and possesses remarkable stability, substantially outperforming the commercial Pt/C catalyst.

Unraveling the High-Activity Origin of Single-Atom Iron Catalysts for Organic Pollutant Oxidation via Peroxymonosulfate Activation.

Single-atom catalysts (SACs) have emerged as efficient materials in the elimination of aqueous organic contaminants; however, the origin of high activity of SACs still remains elusive. Herein, we identify an 8.1-fold catalytic specific activity (reaction rate constant normalized to catalyst's specific surface area and dosage) enhancement that can be fulfilled with a single-atom iron catalyst (SA-Fe-NC) prepared via a cascade anchoring method compared to the iron nanoparticle-loaded catalyst, resulting in one of the most active currently known catalysts in peroxymonosulfate (PMS) conversion for organic pollutant oxidation. Experimental data and theoretical results unraveled that the high-activity origin of the SA-Fe-NC stems from the Fe-pyridinic N4 moiety, which dramatically increases active sites by not only creating the electron-rich Fe single atom as the catalytic site but also producing electron-poor carbon atoms neighboring pyridinic N as binding sites for PMS activation including synchronous PMS reduction and oxidation together with dissolved oxygen reduction. Moreover, the SA-Fe-NC exhibits excellent stability and applicability to realistic industrial wastewater remediation. This work offers a novel yet reasonable interpretation for why a small amount of iron in the SA-Fe-NC can deliver extremely superior specific activity in PMS activation and develops a promising catalytic oxidation system toward actual environmental cleanup.

Highly active and stable Ir nanoclusters derived from Ir1/MgAl2O4 single-atom catalysts.

Single-atom catalysts (SACs) prepared by the atom trapping method often possess high stability yet have limited advantages regarding catalytic performance due to the strong metal-support interaction. Using these SACs as seeds to develop supported nanoclusters or nanoparticles has, however, been proven to be effective in improving the catalysts' intrinsic activity. Herein, we have prepared extremely stable Ir SACs supported by MgAl2O4 via atomic trapping and used them as seeds to fabricate highly active and stable Ir nanocluster catalysts by high-temperature reduction. The activity toward N2O decomposition increased by more than ten times compared with that of the parent Ir SACs. This study provides a new avenue to design and develop highly active and stable catalysts for industrial use.

Exceptional Electrochemical HER Performance with Enhanced Electron Transfer between Ru Nanoparticles and Single Atoms Dispersed on a Carbon Substrate.

Precisely regulating the electronic structures of metal active species is highly desirable for electrocatalysis. However, carbon with inert surface provide weak metal-support interaction, which is insufficient to modulate the electronic structures of metal nanoparticles. Herein, we propose a new method to control the electrocatalytic behavior of supported metal nanoparticles by dispersing single metal atoms on an O-doped graphene. Ideal atomic metal species are firstly computationally screened. We then verify this concept by deposition of Ru nanoparticles onto an O-doped graphene decorated with single metal atoms (e.g., Fe, Co, and Ni) for hydrogen evolution reaction (HER). Consistent with theoretical predictions, such hybrid catalysts show outstanding HER performance, much superior to other reported electrocatalysts such as the state-of-the-art Pt/C. This work offers a new strategy for modulating the activity and stability of metal nanoparticles for electrocatalysis processes.

Engineering Sensitized Photon Upconversion Efficiency via Nanocrystal Wavefunction and Molecular Geometry.

Triplet energy transfer from inorganic nanocrystals to molecular acceptors has attracted strong attention for high-efficiency photon upconversion. Here we study this problem using CsPbBr3 and CdSe nanocrystals as triplet donors and carboxylated anthracene isomers as acceptors. We find that the position of the carboxyl anchoring group on the molecule dictates the donor-acceptor coupling to be either through-bond or through-space, while the relative strength of the two coupling pathways is controlled by the wavefunction leakage of nanocrystals that can be quantitatively tuned by nanocrystal sizes or shell thicknesses. By simultaneously engineering molecular geometry and nanocrystal wavefunction, energy transfer and photon upconversion efficiencies of a nanocrystal/molecule system can be improved by orders of magnitude.

Stable Potential Windows for Long-Term Electrocatalysis by Manganese Oxides Under Acidic Conditions.

Efficient, earth-abundant, and acid-stable catalysts for the oxygen evolution reaction (OER) are missing pieces for the production of hydrogen via water electrolysis. Here, we report how the limitations on the stability of 3d-metal materials can be overcome by the spectroscopic identification of stable potential windows in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. We demonstrate the benefits of this approach using gamma manganese oxide (γ-MnO2 ), which shows no signs of deactivation even after 8000 h of electrolysis at a pH of 2. This stability is vastly superior to existing acid-stable 3d-metal OER catalysts, but cannot be realized if there is a deviation as small as 50-mV from the stable potential window. A stable voltage efficiency of over 70 % in a polymer-electrolyte membrane (PEM) electrolyzer further verifies the availability of this approach and showcases how materials previously perceived to be unstable may have potential application for water electrolysis in an acidic environment.

A 3D Covalent Organic Framework with Exceptionally High Iodine Capture Capability.

Using porous materials to cope with environmental issues is promising but remains a challenge especially for removing the radioactive vapor wastes in fission because of harsh adsorption conditions. Here we report a new, stable covalent organic framework (COF) as a porous platform for removing iodine vapor-a major radioactive fission waste. The three-dimensional COF consists of a diamond topology knotted by adamantane units, creates ordered one-dimensional pores and are highly porous. The COF enables the removal of iodine vapor via charge transfer complex formation with the pore walls to achieve exceptional capacity. Moreover, the 3D COF is "soft" to trigger structural fitting to iodine while retaining connectivity and enables cycle use for many times while retaining high uptake capacity. These results set a new benchmark for fission waste removal and suggest the great potential of COFs as a designable porous material for challenging world-threatening pollution issues.

Small-Protein-Stabilized Semiconductor Nanoprobe for Targeted Imaging of Cancer Cells.

Recently, semiconductor nanoparticles such as quantum dots (QDs) have attracted significant attention for bioimaging. Complex chemical functionalization, surface modification, and bioconjugation chemistry are generally required to tag biomolecules to QDs for imaging of different biomarkers. In this study, we report a simple method for production of QDs stabilized by the small protein, Affibody (AF-QDs) for fluorescent imaging of the human epidermal growth factor receptor type 2 (HER2) in human A549 lung cancer cells. This one-pot synthesis of AF-QDs avoids complex chemical conjugation procedures and demonstrates a promising approach for the preparation of fluorescent nanoprobes for imaging of cancer targets.

Origin of the high performance in GeTe-based thermoelectric materials upon Bi2Te3 doping.

As a lead-free material, GeTe has drawn growing attention in thermoelectrics, and a figure of merit (ZT) close to unity was previously obtained via traditional doping/alloying, largely through hole carrier concentration tuning. In this report, we show that a remarkably high ZT of ∼1.9 can be achieved at 773 K in Ge0.87Pb0.13Te upon the introduction of 3 mol % Bi2Te3. Bismuth telluride promotes the solubility of PbTe in the GeTe matrix, thus leading to a significantly reduced thermal conductivity. At the same time, it enhances the thermopower by activating a much higher fraction of charge transport from the highly degenerate Σ valence band, as evidenced by density functional theory calculations. These mechanisms are incorporated and discussed in a three-band (L + Σ + C) model and are found to explain the experimental results well. Analysis of the detailed microstructure (including rhombohedral twin structures) in Ge0.87Pb0.13Te + 3 mol % Bi2Te3 was carried out using transmission electron microscopy and crystallographic group theory. The complex microstructure explains the reduced lattice thermal conductivity and electrical conductivity as well.

Single Atom Iridium Decorated Nickel Alloys Supported on Segregated MoO2 for Alkaline Water Electrolysis.

Hetero-interface engineering has been widely employed to develop supported multicomponent catalysts for water electrolysis, but it still remains a substantial challenge for supported single atom alloys. Herein a conductive oxide MoO2 supported Ir1 Ni single atom alloys (Ir1 Ni@MoO2 SAAs) bifunctional electrocatalysts through surface segregation coupled with galvanic replacement reaction, where the Ir atoms are atomically anchored onto the surface of Ni nanoclusters via the Ir-Ni coordination accompanied with electron transfer from Ni to Ir is reported. Benefiting from the unique structure, the Ir1 Ni@MoO2 SAAs not only exhibit low overpotential of 48.6 mV at 10 mA cm-2 and Tafel slope of 19 mV dec-1 for hydrogen evolution reaction, but also show highly efficient alkaline water oxidation with overpotential of 280 mV at 10 mA cm-2 . Their overall water electrolysis exhibits a low cell voltage of 1.52 V at 10 mA cm-2 and excellent durability. Experiments and theoretical calculations reveal that the Ir-Ni interface effectively weakens hydrogen binding energy, and decoration of the Ir single atoms boost surface reconstruction of Ni species to enhance the coverage of intermediates (OH*) and switch the potential-determining step. It is suggested that this approach opens up a promising avenue to design efficient and durable precious metal bifunctional electrocatalysts.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic.

The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)Ox, and (NiZr)Ox, we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an "encapsulated exsolution" phenomenon observed upon reducing the metastable porous (Ni0.07Al0.93)Ox to create ultra-stable Ni nanoparticles embedded within the walls of porous Al2O3 nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO2 reforming of methane, maintaining constant 96% CH4 and CO2 conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.

Atomically dispersed hexavalent iridium oxide from MnO2 reduction for oxygen evolution catalysis.

Hexavalent iridium (IrVI) oxide is predicted to be more active and stable than any other iridium oxide for the oxygen evolution reaction in acid; however, its experimental realization remains challenging. In this work, we report the synthesis, characterization, and application of atomically dispersed IrVI oxide (IrVI-ado) for proton exchange membrane (PEM) water electrolysis. The IrVI-ado was synthesized by oxidatively substituting the ligands of potassium hexachloroiridate(IV) (K2IrCl6) with manganese oxide (MnO2). The mass-specific activity (1.7 × 105 amperes per gram of iridium) and turnover number (1.5 × 108) exceeded those of benchmark iridium oxides, and in situ x-ray analysis during PEM operations manifested the durability of IrVI at current densities up to 2.3 amperes per square centimeter. The high activity and stability of IrVI-ado showcase its promise as an anode material for PEM electrolysis.