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In situ imaging of LiO2 dynamics in LOBs with Au/CNT cathode was conducted by ETEM. During discharge, LiO2 formed from Li15Au4 seeds with stability for several minutes. The de-activation of Lifacilitates the nucleation and stabilization of LiO2.

A nanoscale Li-ion battery was constructed with a single MnO@C nanorod and the lithiation process during electrochemical reaction were in situ visualized in an aberration-corrected environmental transmission electron microscope.

As a refractory transition-metal diboride, monolithic TiB2 oxidizes at temperatures below 400 °C. Here, we performed detailed microstructural investigations to study the low-temperature oxidation mechanism of monolithic TiB2. An anomalous rapid oxidation behavior is observed at ∼ 500 °C, where the oxidation rate is much higher than that at a higher temperature of 650 °C. The anomalous rapid oxidation behavior originates from an unreported bi-layer oxide scale consisting of outer homogeneous B2O3/TiO2 mixed layer with a supra-nanometre-sized dual-phase amorphous-crystal microstructure and inner unstable Ti-B-O amorphous layer. By contrast, the oxide scale changes from homogeneous mixed microstructure to a laminated configuration at 650 °C, restoring the superior oxidation resistance. Our experimental results indicate that it is the configuration of the oxide scale that determines primarily the oxidation behavior of TiB2, which has been seldom envisaged in previous studies.

Rechargeable lithium-carbon dioxide (Li-CO2) batteries have attracted much attention due to their high theoretical energy densities and capture of CO2. However, the electrochemical reaction mechanisms of rechargeable Li-CO2 batteries, particularly the decomposition mechanisms of the discharge product Li2CO3 are still unclear, impeding their practical applications. Exploring electrochemistry of Li2CO3 is critical for improving the performance of Li-CO2 batteries. Herein, in-situ environmental transmission electron microscopy (ETEM) technique was used to study electrochemistry of Li2CO3 in Li-CO2 batteries during discharge and charge processes. During discharge, Li2CO3 was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes (CNTs) and Ag nanowires (Ag NWs), but it was hard to decompose during charging at room temperature. To promote the decomposition of Li2CO3, the charge reactions were conducted at high temperatures, during which Li2CO3 was decomposed to lithium with release of gases. Density functional theory (DFT) calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li2CO3. This study not only provides a fundamental understanding to the high temperature Li-CO2 nanobatteries, but also offers a valid technique, i.e., discharging/charging at high temperatures, to improve the cyclability of Li-CO2 batteries for energy storage applications.

Summary Developing outstanding radiation-resistant materials with excellent thermal and mechanical properties and self-healing ability remains a great challenge for advanced nuclear energy systems. Here, we incorporate three-dimensional (3D) carbon nanotube (CNT) networks into iron nanocrystals (Fe NCs) to obtain functional bulk Fe-CNT nanocomposites, exhibiting much higher thermal conductivity and mechanical properties than the Fe NCs without sacrificing strength. Irradiations by energetic helium (He) and krypton ions show that 3D CNT networks act as gigantic-capacity “nano-dustbins” to collect and store He atoms and defects via a “loading-transporting-unloading” mechanism in the grain boundary-CNT (GB-CNT) configuration, thus greatly enhancing their radiation tolerance compared with the Fe NC counterparts. The energetic landscape of interactions of He/defects with the GBs and the Fe-CNT interfaces in the nanocomposites are revealed by first-principles calculations. This work offers a promising strategy for material design of high-performance structural materials for future advanced nuclear reactors.

Single-atom catalysts (SACs) have attracted much attention due to their outstanding catalytic performance in heterogeneous catalysis. Here, we report a template sacrificial method to fabricate an a...

Akin to Li, Na deposits in a dendritic form to cause short circuit in Na metal batteries. However, the growth mechanisms and related mechanical properties of Na dendrites remain largely unknown. He...

High-entropy carbides (HECs) are novel advanced materials composed of covalently bonded multicomponent transition metals and carbon. The transition metal atoms of all the precursor components are randomly distributed at the cation sublattice. Recently, a series of HECs with a non-stoichiometric compound (NSC) as one of the precursors have been synthesized. However, the effect of vacancies on the formation of HECs has not been addressed well. In this paper, NbC0.5 was selected as the NSC to study the interfacial diffusion behavior of NbC0.5 and other covalent transition metal compounds (MCs: M represents one of V, Ti, Ta, and W). The presence of vacancies resulted in a carbon concentration gradient, reduced the diffusion activation energy of metal atoms in NbC0.5–MC and increased the diffusion driving force. In addition, the diffusion process of WC in NbC0.5 was analyzed. Phase transformation of WC to W2C was found during diffusion. The experiment proves that HECs may be easily prepared with the participation of the NSCs, and this work provides the theoretical basis for the alloying of covalent transition metal compounds.

Lithium metal is considered the ultimate anode material for future rechargeable batteries1,2, but the development of Li metal-based rechargeable batteries has achieved only limited success due to uncontrollable Li dendrite growth3–7. In a broad class of all-solid-state Li batteries, one approach to suppress Li dendrite growth has been the use of mechanically stiff solid electrolytes8,9. However, Li dendrites still grow through them10,11. Resolving this issue requires a fundamental understanding of the growth and associated electro-chemo-mechanical behaviour of Li dendrites. Here, we report in situ growth observation and stress measurement of individual Li whiskers, the primary Li dendrite morphologies12. We combine an atomic force microscope with an environmental transmission electron microscope in a novel experimental set-up. At room temperature, a submicrometre whisker grows under an applied voltage (overpotential) against the atomic force microscope tip, generating a growth stress up to 130 MPa; this value is substantially higher than the stresses previously reported for bulk13 and micrometre-sized Li14. The measured yield strength of Li whiskers under pure mechanical loading reaches as high as 244 MPa. Our results provide quantitative benchmarks for the design of Li dendrite growth suppression strategies in all-solid-state batteries. Lithium whisker growth and mechanical properties can be studied in situ using a combination of two microscopies.

Li–CO2 batteries are promising energy storage devices owing to their high energy density and possible applications for CO2 capture. However, still some critical issues, such as high charging overpotential and poor cycling stability caused by the sluggish decomposition of Li2CO3 discharge products, need to be addressed before the practical applications of Li–CO2 batteries. Exploring highly efficient catalysts and understanding their catalytic mechanisms for the CO2 reduction reaction (CORR) and evolution reaction (COER) are critical for the application of Li–CO2 batteries. However, the direct imaging of electrocatalysis during CORR and COER is still elusive. Herein, we report the in situ imaging of electrocatalysis during CORR and COER in a Li–CO2 nanobattery using a Ni–Ru-coated α-MnO2 nanowire (Ni–Ru/MnO2) cathode in an advanced aberration corrected environmental transmission electron microscope. During the CORR, a thick Li2CO3 and carbon mixture layer was formed on the surface of the Ni–Ru/MnO2 nanowires via 4Li+ + 3CO2 + 4e− → 2Li2CO3 + C. During the COER, the as-formed Li2CO3 decomposed via 2Li2CO3 → 2CO2 + O2 + 4Li+ + 4e−, while the as-formed amorphous carbon remained. In contrast, the decomposition of Li2CO3 on bare MnO2 nanowires was difficult, underscoring the important Ni–Ru bimetal electrocatalytic role in facilitating the COER. Our results provide an important understanding of the CO2 chemistry in Li–CO2 batteries, possibly helping in the designing of Li–CO2 batteries for energy storage applications.

It is a highly relevant topic concerning how to improve the electrochemical performance of anode materials for the next generation lithium-ion batteries (LIBs). Herein, for the first time, we report a facile and controllable approach to modify MoS2 nanosheets, a typical 2D material, as an anode material for advanced LIBs via oxygen plasma engineering. An oxygen plasma treatment not only generates vacancies/defects but also incorporates heteroatom doping to form Mo–O–C bonds. This unique hybrid specialty enables the oxygen-plasma-treated MoS2 to achieve superior electrochemical performance with high reversible capacities, a long-term cycle life, and good rate capabilities. The plasma-assisted modification is believed to be applicable for other 2D materials as an efficient anode for energy storages.

Metal-air batteries have much higher theoretical energy density than metal ion batteries, however, their application is hampered by the sluggish oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). As such, electrocatalysis is employed to facilitate the ORR and OER. Despite enormous efforts, real time imaging of the electrocatalysis during the ORR and OER processes remain elusive. Furthermore, it is controversial whether or not electrocatalysis is necessary in the Na-O2 battery. Here we show the first in-situ imaging of the operation of the electrocatalysis in a Na-O2 battery in an advanced aberration corrected environmental transmission electron microscopy (ETEM). In the Au-coated MnO2 nanowire air cathode, the ORR is characterized by the formation of NaO2 nano bubbles nucleated from the Au catalysts, causing an 18 times volume increase on the surface of the MnO2 nanowires; the NaO2 quickly disproportionated to Na2O2 and O2, causing collapse of the NaO2 nano bubbles. In contrast, no ORR took place in the bare MnO2 nanowire cathode; instead, the MnO2 nanowires only swelled 217% as a result of the Na+ intercalation. The results provide not only new insight into the Au-catalyzed oxygen chemistry in the Na-O2 battery, but also an atom-level characterization technique to evaluate the electrocatalysis in the metal air batteries.

Ultra-fine-grained (UFG) metals and alloys have unique mechanical properties at room temperature. However, their grains grow rapidly even at low and mediate temperatures due to the high density of grain boundaries which largely increase their Gibbs free energy. Thus, improving the thermal stability of UFG metals and alloys should be critical to their processing and application at elevated temperatures. In this report, the thermal stability of UFG Ni alloys is studied by changing the type and content of such solutes as Fe, Cr and V. The thermal stability is theoretically predicted by the change in free energy due to solute segregation and by the normalized grain boundary free energy. The thermal stability is also experimentally examined by the change in microhardness after annealing. The experimental results agree well with the theoretical predictions. The thermal stability of UFG Ni is significantly improved by the grain boundary segregation of V and moderately improved by the grain boundary segregation of Cr and Fe. Furthermore, increasing the content of solute improves the thermal stability of UFG Ni(Cr) alloys. Our study should help design UFG Ni alloys with improved thermal stability for practical applications.

Improving the radiation resistance of structural materials in the presence of helium is significant for the development of advanced nuclear power systems. Nanostructured materials reduce the grain size and significantly increase the grain boundary density. Hence, it is considered to be an effective method to improve the radiation resistance of materials. In this work, we studied the radiation resistance of nanocrystalline (NC) and coarse grained (CG) 304 austenitic stainless steel (304-SS) by helium ion irradiations. The mean grain sizes of NC and CG 304-SS are ∼45 nm and ∼30 μm, respectively. The results of positron annihilation Doppler broadening spectroscopy and transmission electron microscopy indicate that NC 304-SS not only has better swelling resistance than CG 304-SS, but also has better helium effect resistance. And the swelling of NC 304-SS is reduced by a factor of ∼5.7 compared with CG 304-SS under the irradiation of 170 keV He+ to 2 × 1020 ions m−2 at 723 K. The mechanisms for the excellent swelling resistance of NC 304-SS are discussed.

Austenitic stainless steel has high potential as nuclear and engineering materials, but it is often coarse grained and has relatively low yield strength, typically 200–400 MPa. We prepared a bulk nanocrystalline lanthanum-doped 304L austenitic stainless steel alloy by a novel technique that combines mechanical alloying and high-pressure sintering. The achieved alloy has an average grain size of 30 ± 12 nm and contains a high density (~1024 m−3) of lanthanum-enriched nanoprecipitates with an average particle size of approx. 4 nm, leading to strong grain boundary strengthening and dispersion strengthening effects, respectively. The yield strength of nano-grained and nano-precipitated stainless steel reaches 2.9 GPa, which well exceeds that of ultrafine-grained (100–1000 nm) and nano-grained (

Low-cost metal sulfides are promising anode materials for sodium-ion batteries (SIBs); however, they suffer from sluggish kinetics and large volume expansion upon cycling. Here, a strategy to grow FeS2 on turbostratic carbon (t-carbon) assisted by chemical interactions between Fe and C electrons was realized via a simple and scalable mechanical alloying (MA) approach with a trace amount of CNTs. The structural change in CNTs synchronized with the in situ growth of FeS2 on the transformed t-carbon during the MA process, forming localised FeS2 nanocrystals wrapped in the frameworks of t-carbon. This intertwined structure within a grain consisted of chemical bonding by electronic hybridization between FeS2 and its adjacent carbon layer, resulting in enhanced structural stability upon cycling. Moreover, the localised FeS2 nanocrystals with an ultrasmall diameter of 10 nm encapsulated in the nanoframeworks of t-carbon could effectively shorten the diffusion paths of electrons/ions and withstand the volume expansion. The as-synthesized FeS2–C hybrid composite electrode exhibited a pseudocapacitive diffusion behavior with high specific capacity, good cycling stability, and remarkable rate capability. This strategy is a facile, scalable, and low-cost route toward high-performance metal sulfide anode materials for the commercial utilization of SIBs.

It is a challenge to obtain high specific capacitance and high energy density for carbon materials applied in energy storage. In this work, a metal-organic framework (MOF) with high surface area (1149 m2 g−1) is used for the design of Co/C nanocomposites. Ni(OH)2@Co/C nanocomposites with core/shell structure are synthesized by carbonizing MOF nanoparticles to form the cores of Co/C and growing 2-dimensional Ni(OH)2 nanosheets on the surfaces, as the shells. The Ni(OH)2@Co/C nanocomposites exhibit excellent electrochemical properties, including high specific capacitance (952 F g−1, 0.5 A g−1), high-rate dischargeability (692 F g−1, 20 A g−1), and good cycle stability (84%, 10000th cycles), being ascribed to the combined effect of the components and the structure characteristics, i.e., Ni(OH)2 ultrathin nanosheets for high capacitance, Co nanoparticles for high rate dischargeability and nanoporous carbon for excellent cycle life. The asymmetric supercapacitor assembled with the Ni(OH)2@Co/C materials and active carbon presents a higher energy density of 33.6 Wh kg−1 at 516.3 W kg−1. The simple but powerful design routine will be beneficial to the application of MOF in such energy storage filed as battery and supercapacitor.

Nitride materials are of considerable interest due to their fundamental importance and practical applications. However, synthesis of transition metal nitrides often requires extreme conditions, e.g., high temperature and/or high pressure, slowing down the experimental discovery. Using global structure search methods in combination with first-principles calculations, we systematically explore the stoichiometric phase space of iron–nitrogen compounds on the nitrogen-rich side at ambient and high pressures up to 100 GPa. Diverse stoichiometries in the Fe–N system are found to emerge in the phase diagram at high pressures. Significantly, FeN4 is found to be stable already at ambient pressure. It undergoes a polymerization near 20 GPa which results in a high energy density. Accompanying the polymerization, FeN4 transforms from a direct band gap semiconductor to ferromagnetic metal. We also predict several phase transitions in FeN and FeN2 at high pressure, and the results explain the previous experimental obse...

Coarse-grained high-entropy alloys (HEAs) have such excellent mechanical properties as high hardness and strength. The well-known Hall-Petch relation suggests that this high hardness should be further increased if the crystallite size of HEAs is decreased to nanometer scale. We prepared single-phased nanocrystalline (NC) refractory VNbMoTaW HEAs powders by mechanical alloying (MA). The achieved NC HEAs have a body-centered cubic (BCC) structure and an average grain size of approx. 6 nm. We further used a high-pressure/high-temperature (HPHT) technique to consolidate the NC powders to achieve bulk NC HEAs. The evolution of phases, microstructure and mechanical properties of the consolidated bulk NC HEAs were studied as a function of consolidating temperature. The bulk NC VNbMoTaW HEAs consolidated at an optimized temperature of 1150 °C have an average grain size of ∼30 nm and a hardness of 11.4 GPa, ∼ twice that of coarse-grained refractory HEAs. This ultrahigh hardness has three origins: solid solution, grain boundary and dislocation hardening.

Carbon dioxide (CO2) as a greenhouse gas causes globe warming. Recent studies have shown that CO2 can be harnessed to make an energy storage device through the operation of metal-CO2 batteries. While the Li-CO2 and Na-CO2 batteries showing high capacity and good cycle life have been demonstrated, the possibility of creating a K-CO2 battery has not been realized. Here we report the creation of a K-CO2 battery by using CO2 as the cathode in an advanced aberration corrected environmental transmission electron microscope, and in-situ observation of the discharge and charge processes of the nanobattery. During discharge, K2CO3 was generated in the cathode, which converted back to metal K during charge, and the K-CO2 nanobattery demonstrates a good cyclability. Moreover, it is evident that CO gas was released during discharge and the carbon cathode was consumed continuously during charge. Our study provides a fundamental understanding of the K-CO2 battery, which may aid the designing of K-CO2 based energy storage devices.

Annealing often causes softening in conventional large-grained materials. However, annealing has been found to cause hardening in many nanocrystalline metals and alloys. This abnormal hardening by annealing has been explained by such factors as solute segregation at grain boundaries, grain boundary relaxation, grain boundary pinning by second phase particles, etc. In the present work, a homogenous single-phase nanocrystalline Ni(Fe) alloy prepared by electrodeposition was investigated. This alloy is with approx. 1 at% Fe and composed of a solid solution of Fe in Ni without any precipitated phase. The goal is to shed light on which mechanism dominates annealing hardening. Microhardness of the alloy was found to increase slightly just before the grains started to grow during annealing. In addition, long time annealing at the hardening temperature resulted in the decrease of hardness due to grain growth. Both lattice parameter and atom probe tomography studies suggest that the annealing hardening is caused by the segregation of solute and impurity atoms on grain boundaries in the nanocrystalline Ni(Fe) alloy.

We report real time imaging of the oxygen reduction reactions (ORRs) in all solid state sodium oxygen batteries (SOBs) with CuO nanowires (NWs) as the air cathode in an aberration-corrected environmental transmission electron microscope under an oxygen environment. The ORR occurred in a distinct two-step reaction, namely, a first conversion reaction followed by a second multiple ORR. In the former, CuO was first converted to Cu2O and then to Cu; in the latter, NaO2 formed first, followed by its disproportionation to Na2O2 and O2. Concurrent with the two distinct electrochemical reactions, the CuO NWs experienced multiple consecutive large volume expansions. It is evident that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter one-electron-transfer ORR, leading to the formation of NaO2. Remarkably, no carbonate formation was detected in the oxygen cathode after cycling due to the absence of carbon source in the whole battery setup. These results provide fundamental unde...

At room temperature, a large negative out-of-plane magnetoresistance (MR), [R(H)-R(0)]/R(0), with a value of −35.76% at magnetic field of 9 T has been obtained in the cobalt ferrite (CoFe2O4)/polyaniline (PANI) nanocomposites with CoFe2O4 loading of 40.0 wt% prepared by surface initiated polymerization (SIP) method, which is strongly related to the weak localization (WL) model in the weak disordered system. The negative MR at room temperature in the CoFe2O4/PANI nanocomposites exhibits the obvious nanoparticle loading and magnetic field dependent properties. Both thermal activated transport model and Mott variable range hopping (VRH) model are applied to express the electrical transport mechanism for the temperature regimes of 180–290 K and 50–180 K, accordingly. The electrical transport in the CoFe2O4/PANI nanocomposites obeys the 3D VRH transport mechanism at low temperature range of 50–180 K. The estimated activation energy Eg for the CoFe2O4/PANI nanocomposites with different CoFe2O4 nanoparticle loadings of 10.0, 20.0, 40.0, and 60.0 wt% is 61, 63, 65, and 87 meV, respectively. The coating of PANI on the surface of CoFe2O4 nanoparticle reveals the significant effect on both the remanence and coercivity of CoFe2O4 nanoparticle.

Using surface photovoltaic and electric-field-induced surface photovoltaic techniques, as well as a CASTEP simulation method, we have studied the photo-excited and field-induced charge transfer (CT) behaviors of anatase nano-TiO2 particles adsorbed by O2, N2, and water vapor. Our results suggest that the photo-generated carriers transport process is strongly influenced by the adsorbates on the TiO2 nanoparticles. Oxygen molecules enhance the main-band-gap CT transition at 345 nm and inhibit the sub-band-gap CT transition at 419 nm. This can be explained by the 1 π g electrons in adsorbed O2 and the widened bandgap after adsorbing O2. Nitrogen molecules inhibit the main-band-gap and the sub-band-gap CT transitions differently. This can be explained by the 3 σ g and 1 π g electrons of adsorbed N2, which may cause more new surface states in between the bandgap and decrease the valence band edge of nano-TiO2, as suggested by the CASTEP simulation. The influence of adsorbed water molecule on the main-band-gap CT transition is much stronger than that on the sub-band-gap CT transition.

As one of the most promising first wall/blanket structure materials in fusion reactors, oxide dispersion strengthened (ODS) ferritic steel has been extensively studied in past decades. However, the grain size of ODS steels is often ultrafine-grained (UFG, between 200 and 1000 nm). Refining their grain size, if possible, should further enhance their radiation tolerance. In the present work, we report on a novel zirconium-doped nanocrystalline (NC) 14YWTZ ODS steel composed of a ferritic matrix with an average grain size of 50 nm and high-density oxide nanoprecipitates with an average diameter of 3.3 nm. Both NC and UFG 14YWT ODS steels were irradiated with helium ions at 450 °C. Abnormal lattice shrinking and narrowing of X-ray diffraction peaks are found in irradiated NC ODS steel. The NC ODS steel has an extremely high sink strength of ∼ 3 × 1016 m−2, which is mainly contributed by grain boundaries and effectively inhibits the aggregation of He atoms and the growth of He bubbles. The bubble size, void swelling, and irradiation hardening in NC ODS steel irradiated at a high dose, when compared to those in UFG ODS steel, are significantly smaller. The underlying mechanisms for the high irradiation tolerance in the NC ODS steel are discussed. This work provides an approach to further enhancing the radiation resistance of conventional UFG ODS steels by refining their grain size to nanoscale dimensions.

Oxide dispersion strengthened (ODS) alloys containing high-density nano-oxides show excellent mechanical properties and irradiation tolerance. However, ODS alloys are often ultrafine-grained materials since the grain size of matrix is located between 100 and 1000 nm. Here, nanocrystalline and ultrafine-grained ODS alloys with different grain sizes (50 nm and 300 nm) were prepared by mechanical alloying and high-pressure consolidation techniques, which show exceptional thermal stability. To understand their irradiation response, the two alloys were irradiated with 400 keV helium ions to a fluence of 1 × 1017He+ /cm2 at 350 ℃, 400 ℃ and 450 ℃. The results show that the size and volume fraction of helium bubbles in nanocrystalline ODS alloys increase when the irradiation temperature increases from 350 ℃ to 450 ℃. Grain boundaries (GBs) play a key role in bubble formation and evolution. We identified the bubble denuded zone (BDZ) near the GBs, but the width of the denuded zone narrowed and finally vanished with increasing helium concentration. Nanocrystalline ODS alloy with 50 nm grains (Y50) can disperse helium into much finer bubbles than ultrafine-grained ODS alloy with 300 nm grains (Y300) because of the extremely high density of GBs and oxide-matrix boundaries. To our best knowledge, Y50 alloy presents the best helium bubble suppression ability among all studied ODS and nanostructured ferritic alloys (NFA), which makes it a promising candidate material for using in fission and fusion nuclear reactors.

Multicomponent vanadium-based alloys (MVAs), often considered as conventional coarse-grained alloys, have been extensively studied in past decades as important metal hydride electrodes and solid state hydrogen storage materials. A micron-scale microstructure composed of a V-based main phase and a TiNi-based secondary phase has been often used to explain the electrochemical performance of MVAs, where the micron-scale TiNi-based secondary phase with a three-dimensional network is considered as a catalyst for electrochemical reaction and/or a current collector. However, the atomic-scale microstructure of MVAs has been largely unknown to date. Here, using advanced aberration corrected electron microscopy, we have found micron-/nano-scale hierarchical structures in an as-cast MVA, V0.35Cr0.1Ti0.25Ni0.3. The micron-scale TiNi-phase contains VCr nanoprecipitates whereas the micron-scale VCr-phase contains TiNi nanoprecipitates and Ni-rich nanoclusters. In addition, we have found that the nanoprecipitates plays an essential role in the hydrogen storage, namely, TiNi nanoprecipitates with a diameter of approx. 30 nm absorb hydrogen faster than their VCr-matrix. Our studies revise conventional understanding on the microstructures in MVAs and the hydrogen storage mechanism, which may guide the development of nanostructured hydrogen storage materials for practical applications

Designing low-cost oxygen reduction reaction (ORR) electrocatalysts to replace platinum group metal holds great promise for boosting the wide use of metal-air batteries. Herein, atomically dispersed iron supported on nitrogen-doped carbon (A-Fe-NC) was fabricated via an effective ligand-stabilized pyrolysis strategy. Owing to the high density of the active sites and the two-dimensional (2-D) nanosheet structure, the as-prepared A-Fe-NC electrocatalyst delivers excellent ORR performance with a positive half-wave potential of 0.865 V in alkaline solution, which is superior to that of Pt/C (0.82 V vs RHE). Moreover, the primary Zn-air battery assembled with the A-Fe-NC delivered an ultrahigh specific power of 132.2 mW cm−2 and stable long-term operation. It also displayed robust charging-discharging cycling performance with voltage gap of 0.83 V after 240 h, lower than that of the Pt/C + RuO2 electrode (0.95 V). To reveal the catalytic mechanism of A-Fe-NC, density functional theory calculation was conducted and the results revealed that the interaction between Fe and nitrogen regulated the electronic structure of active sites, thus improving charge transfer and further promoting the electrocatalytic reactivity for ORR. This work provided a facile and effective strategy for constructing Fe/N codoped 2-D carbon nanocomposite as high performance electrocatalysts for energy conversion.

Nanocrystalline metals, e.g., Mg, are often strong but with a low thermal stability. In this study, six solute elements, Ti, Zr, Ta, Co, Cr, La, which are immiscible in Mg under equilibrium conditions, are mechanically alloyed with Mg to study the extension of solid solubility, the thermal stability and the mechanical properties of nanocrystalline Mg. Extended solid solubility of Ti and Zr solutes in Mg matrix is achieved after mechanical alloying. The nanocrystalline Mg is largely stabilized by Ti, moderately stabilized by Zr, and not stabilized by Ta, Co, Cr and La. The onset temperature for a rapid grain growth increases from 100 °C (0.4 Tm) for nanocrystalline Mg to ~ 350 °C (0.68 Tm) for nanocrystalline Mg0.95Ti0.05 (defined as Mg-5Ti). A relatively small grain size of ~ 145 nm is achieved in Mg-5Ti at 350 °C. The enhanced thermal stability of nanocrystalline Mg-Ti alloy can be attributed to the segregation of Ti atoms at grain boundaries. In addition, an abnormal grain growth is also observed because of the inhomogeneous distribution of solute/impurity atoms. The high thermal stability of nanocrystalline Mg-5Ti alloy enables us to degass the mechanically alloyed powders at a high temperature of 300 °C and achieve a porosity-free nanocrystalline bulk with a compressive yield strength of 183 MPa and a fracture strain of above 0.6.

Nanoparticles have great potentials to improve the strength of metal matrix composites, but unfortunately, they tend to grow at high temperatures and are difficult to disperse uniformly with a high content, limiting the improvement in thermal stability and mechanical properties. Here we show the synthesis and performance of Mg–MgO in situ nanocomposites with a fraction of up to 40 vol% MgO nanoparticles. Our synthetic strategies include reactively cryomilling Mg with oxygen and subsequently consolidating the cryomilled powders under a high pressure of 6 GPa. Dispersed MgO nanoparticles with a fine particle size of 7.8 ± 1.7 nm are mainly situated at grain boundaries and exhibit a strong interfacial bonding with Mg matrix. Because of the strong Zener pinning effect of in situ formed MgO nanoparticles, the thermal stability is largely enhanced from ~ 100 °C for nanocrystalline Mg to 400 °C for Mg–10vol%MgO. The high thermal stability of Mg–MgO enables us to consolidate the cryomilled powders at a high temperature of 500 °C under a pressure of 6 GPa and achieve bulk Mg–MgO nanocomposites with a high compressive yield strength: 562 and 688 MPa for Mg–10vol%MgO and Mg–20vol%MgO, respectively. Meanwhile, the room-temperature hardness of the Mg–MgO nanocomposites increases linearly with the content of MgO nanoparticles and reaches 3.65 GPa for Mg–40vol%MgO. Furthermore, the MgO nanoparticles significantly improve the high-temperature hardness of nanocrystalline Mg.

In this work, nano-structured Mn3O4 particles with spongy-morphology were synthesized through vesicle templating, where hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as cationic-anionic surfactants. The Mn3O4 electrode materials exhibited a high specific capacitance (451 F g−1) at a current density of 0.5 A g−1 in 1 mol L−1 Na2SO4 electrolyte, and retained 333 F g−1 when the current density was increased to 5 A g−1. Its capacitance retention is also high (up to 92%) after 10,000 cycles at a current density of 5 A g−1.

Improving the high-temperature oxidation resistance of steels by excessive Si addition to form a continuous silica healing layer would deteriorate the mechanical, welding and irradiation properties. Here, we report a thermally stable nanocrystalline 304 (NC-304) austenitic stainless steel with a low Si content (less than 1 wt.%) and superior high-temperature oxidation resistance. The segregated Si at the grain boundaries (GBs) of NC-304 presets a nanoscale Si-enriched network for the formation of a continuous SiO2 GB network during the high-temperature oxidation. Besides, the high-density La-Si-O-rich nanoprecipitates can serve as heterogeneous formation sites for SiO2, promoting the formation of a continuous SiO2 phase along the GB network. The unique nanocrystalline microstructure and element distribution feature of Si in NC-304 accelerate the construction of a continuous SiO2 healing layer, which effectively eliminates the breakaway oxidation found in coarse-grained 304 counterpart and significantly reduces the high-temperature oxidation rate at least to 1000 °C.

A local structure determines the properties in disordered solid solutions with simple crystal structure. Introducing a weak enthalpy-interaction-element will change the local structure evolution of refractory high-entropy alloy films, thereby bringing effects for the properties. Herein series of (NbMoTaW)100-xVx (x = 0 ~ 30.5, at%) thin films were prepared by radio frequency magnetron sputtering, and systematic investigations of the films are carried out through combining the underlying microstructure, mechanical properties, and resistivity-temperature behavior. Furtherly, in accordance with the cluster-plus-glue-atom model, the present paper interpreted the local structure evolution with the film components changing. The results reveal that the excellent thermal stability of the films is originate from the enthalpy interaction, and the high stability of the refractory element itself. The V addition is free of crystal structure variation in the films, but bringing two-fold effects. The main one is the enhancement of the microstructural homogeneity by increasing the disorder degree. The other is weakening interatomic interactions as well as enabling the films more unstable due to the increasing system energy. The refractory high-entropy films can be promising candidates for high temperature, high hardness, and wear-resistance applications, e.g., high-temperature-bearing structures, heat-protection systems, diffusion barriers, and film resistors.

The photogenerated carriers’ transport and microstructure of self-assembled core–shell ZnSe/ZnS/L-Cys quantum dots (QDs), which was synthesized at room temperature, are studied via the surface photovoltaic and transient photovoltaic techniques, X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible absorption spectra. The results suggest that the ZnSe nanocrystals prepared at room temperature prefer to nucleate at (111) and (220) faces, and grow a shell–ZnS at (220) face rather than at (311) face. The quantum well depth in some interface space charge region (SCR) of the QDs prepared at room temperature is smaller than that prepared at 90 °C. The evolution of the band bending from a depletion layer to an accumulation layer may occur in the graded-band-gap and at the side of the interface SCR, as compared the QDs with p-type photovoltaic characteristic synthesized at room temperature to that at 90 °C. This electron structural shift may be ascribed to the reduced quantum well depth and then an obvious resonance quantum tunneling of the QDs synthesized at room temperature.

One of the fundamental magnetic properties – the low-temperature magnetization as well as the exchange interactions derived by using a spin-wave excitation theory – has been well studied in glassy ribbons rather than bulk metallic glasses. The paper studies the temperature-dependent magnetization of a bulk Fe 40 Ni 40 P 14 B 6 alloy, derives the range and fluctuation of exchange interactions, and compares these magnetic behaviors with those of well-studied glassy ribbons. The low-temperature magnetization of our bulk glass can be well expressed by a spin-wave excitation theory, which has been widely utilized to study the temperature-dependent magnetization of ferromagnetic glassy ribbons. Moreover, both the derived spin-wave stiffness coefficient and the derived range and fluctuation of exchange interactions in our bulk metallic glass are very similar to those in glassy ribbons, indicative of the similarity in magnetic exchange interaction between bulk metallic glasses and glassy ribbons.