Stable anchoring of single rhodium atoms by indium in zeolite alkane dehydrogenation catalysts.

Maintaining the stability of single-atom catalysts in high-temperature reactions remains extremely challenging because of the migration of metal atoms under these conditions. We present a strategy for designing stable single-atom catalysts by harnessing a second metal to anchor the noble metal atom inside zeolite channels. A single-atom rhodium-indium cluster catalyst is formed inside zeolite silicalite-1 through in situ migration of indium during alkane dehydrogenation. This catalyst demonstrates exceptional stability against coke formation for 5500 hours in continuous pure propane dehydrogenation with 99% propylene selectivity and propane conversions close to the thermodynamic equilibrium value at 550°C. Our catalyst also operated stably at 600°C, offering propane conversions of >60% and propylene selectivity of >95%.

Alkali metal bilayer intercalation in graphene.

Alkali metal (AM) intercalation between graphene layers holds promise for electronic manipulation and energy storage, yet the underlying mechanism remains challenging to fully comprehend despite extensive research. In this study, we employ low-voltage scanning transmission electron microscopy (LV-STEM) to visualize the atomic structure of intercalated AMs (potassium, rubidium, and cesium) in bilayer graphene (BLG). Our findings reveal that the intercalated AMs adopt bilayer structures with hcp stacking, and specifically a C6M2C6 composition. These structures closely resemble the bilayer form of fcc (111) structure observed in AMs under high-pressure conditions. A negative charge transferred from bilayer AMs to graphene layers of approximately 1~1.5×1014 e-/cm-2 was determined by electron energy loss spectroscopy (EELS), Raman, and electrical transport. The bilayer AM is stable in BLG and graphite superficial layers but absent in the graphite interior, primarily dominated by single-layer AM intercalation. This hints at enhancing AM intercalation capacity by thinning the graphite material.

Molybdenum Chloride Nanostructures with Giant Lattice Distortions Intercalated into Bilayer Graphene.

The nanospace of the van der Waals (vdW) gap between structural units of two-dimensional (2D) materials serves as a platform for growing unusual 2D systems through intercalation and studying their properties. Various kinds of metal chlorides have previously been intercalated for tuning the properties of host layered materials, but the atomic structure of the intercalants remains still unidentified. In this study, we investigate the atomic structural transformation of molybdenum(V) chloride (MoCl5) after intercalation into bilayer graphene (BLG). Using scanning transmission electron microscopy, we found that the intercalated material represents MoCl3 networks, MoCl2 chains, and Mo5Cl10 rings. Giant lattice distortions and frequent structural transitions occur in the 2D MoClx that have never been observed in metal chloride systems. The trend of symmetric to nonsymmetric structural transformations can cause additional charge transfer from BLG to the intercalated MoClx, as suggested by our density functional theory calculations. Our study deepens the understanding of the behavior of matter in the confined space of the vdW gap in BLG and provides hints at a more efficient tuning of material properties by intercalation for potential applications, including transparent conductive films, optoelectronics, and energy storage.

Misoriented high-entropy iridium ruthenium oxide for acidic water splitting.

Designing an efficient catalyst for acidic oxygen evolution reaction (OER) is of critical importance in manipulating proton exchange membrane water electrolyzer (PEMWE) for hydrogen production. Here, we report a fast, nonequilibrium strategy to synthesize quinary high-entropy ruthenium iridium-based oxide (M-RuIrFeCoNiO2) with abundant grain boundaries (GB), which exhibits a low overpotential of 189 millivolts at 10 milliamperes per square centimeter for OER in 0.5 M H2SO4. Microstructural analyses, density functional calculations, and isotope-labeled differential electrochemical mass spectroscopy measurements collectively reveal that the integration of foreign metal elements and GB is responsible for the enhancement of activity and stability of RuO2 toward OER. A PEMWE using M-RuIrFeCoNiO2 catalyst can steadily operate at a large current density of 1 ampere per square centimeter for over 500 hours. This work demonstrates a pathway to design high-performance OER electrocatalysts by integrating the advantages of various components and GB, which breaks the limits of thermodynamic solubility for different metal elements.

Unraveling the Reaction Mystery of Li and Na with Dry Air.

Li and Na metals with high energy density are promising in application in rechargeable batteries but suffer from degradation in the ambient atmosphere. The phenomenon that in terms of kinetics, Li is stable but Na is unstable in dry air has not been fully understood. Here, we use in situ environmental transmission electron microscopy combined with theoretical simulations and reveal that the different stabilities in dry air for Li and Na are reflected by the formation of compact Li2O layers on Li metal, while porous and rough Na2O/Na2O2 layers on Na metal are a consequence of the different thermodynamic and kinetics in O2. It is shown that a preformed carbonate layer can change the kinetics of Na toward an anticorrosive behavior. Our study provides a deeper understanding of the often-overlooked chemical reactions with environmental gases and enhances the electrochemical performance of Li and Na by controlling interfacial stability.

Bottom-up evolution of perovskite clusters into high-activity rhodium nanoparticles toward alkaline hydrogen evolution.

Self-reconstruction has been considered an efficient means to prepare efficient electrocatalysts in various energy transformation process for bond activation and breaking. However, developing nano-sized electrocatalysts through complete in-situ reconstruction with improved activity remains challenging. Herein, we report a bottom-up evolution route of electrochemically reducing Cs3Rh2I9 halide-perovskite clusters on N-doped carbon to prepare ultrafine Rh nanoparticles (~2.2 nm) with large lattice spacings and grain boundaries. Various in-situ and ex-situ characterizations including electrochemical quartz crystal microbalance experiments elucidate the Cs and I extraction and Rh reduction during the electrochemical reduction. These Rh nanoparticles from Cs3Rh2I9 clusters show significantly enhanced mass and area activity toward hydrogen evolution reaction in both alkaline and chlor-alkali electrolyte, superior to liquid-reduced Rh nanoparticles as well as bulk Cs3Rh2I9-derived Rh via top-down electro-reduction transformation. Theoretical calculations demonstrate water activation could be boosted on Cs3Rh2I9 clusters-derived Rh nanoparticles enriched with multiply sites, thus smoothing alkaline hydrogen evolution.

Pyridinium-derived polycationic covalent organic polymers for aromatic C-H bond photocatalytic oxidation.

Using oxygen in the air as the sole oxidant to oxidize hydrocarbons into high value-added compounds is a highly promising synthesis strategy with economic advantages. However, the oxidation of hydrocarbons with molecular oxygen under mild conditions is challenging due to the large C-H bond energy in hydrocarbons. Herein, a metal-free two-dimensional covalent organic polymers (COP) functionalized by photoactive pyridinium units has been developed for heterogeneous photocatalytic oxidation of hydrocarbons. This is the first kind of COPs material that can achieve photocatalytic oxidation of hydrocarbons without any additives or stoichiometric oxidants except for the oxygen in the air.

Three-dimensional carbon foam decorated with SnO2 as multifunctional host for lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries with high theoretical capacity and abundant sulfur resources are potential energy storage systems. Nevertheless, there are several roadblocks that strongly limit the commercial application of Li-S batteries, including the insulating nature of sulfur and Li2S, large volume change and the shuttle effect of lithium polysulfides. Herein, a three-dimensional carbon foam (CF) decorated with SnO2 (SnO2/CF) is fabricated by the simple electrodeposition and used as a sulfur host to resolve the bottleneck issues in Li-S batteries. Thanks to the synergetic effect of the polar SnO2 and conductive carbon framework, the SnO2/CF framework is endowed with multifunctionalities such as providing three-dimensional conductive framework, inhibiting the migration of polysulfides and improved reaction kinetics. Consequently, durable cycle performance with a capacity of 458.2 mAh g-1 after 1000 cycles at 1 C is achieved. Furthermore, a high capacity of 749.5 mAh g-1 at a high rate of 5 C is attained. Remarkably, under high sulfur loading of 8.84 mg cm-2, the S@SnO2/CF cathode can still deliver a high specific capacity of 389.8 mAh g-1 after 300 cycles at 0.5 C. This work demonstrates a novel strategy to improve the performance of Li-S batteries for energy storage applications.

Electrochemical Sensor Made with 3D Micro-/Mesoporous Structures of CoNi-N/GaN for Noninvasive Detection of Glucose.

Noninvasive detection of glucose (NGD) is important because ∼10% of the global population is suffering from diabetes. Herein, a three-dimensional (3D) micro-/mesoporous structure, i.e., a CoNi-N nanosheet-coated GaN 3D scaffold (CoNi-N@GaN-3S), was proposed for detecting saliva glucose, where the GaN scaffold can provide a large open surface for nanosheet decoration, while the catalytic nanosheets can increase the surface area and prevent the GaN-3S from anodic corrosion. Moreover, it was found that high-temperature ammoniation of CoNi can lead to dense atomic holes and an N-terminated surface (CoNi-N), which promoted the ionization of CoNi with a higher catalytic activity. It is the first time that dense atomic holes have been observed in CoNi to our knowledge. The designed CoNi-N@GaN-3S sensor was applied to the electrochemical detection of glucose with a low limit of detection (LOD) of 60 nM and a high sensitivity, selectivity, and stability. In addition, detection of human-saliva glucose was realized with an LOD of 5 µM, which was more than 4-fold lower than reported reliable LODs. An integrated sensor with a low consumption of saliva sample was demonstrated for NGD.

Enabling Long Cycle Life and High Rate Iron Difluoride Based Lithium Batteries by In Situ Cathode Surface Modification.

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer-derived carbon (FeF2 @PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod-shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2 @PDC enables a reversible capacity of 500 mAh g-1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2 @PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g-1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3 O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium-ion battery applications.

Two-Dimensional Palladium Phosphoronitride for Oxygen Reduction.

Two-dimensional (2D) catalysts often show extraordinary activity at low mass loading since almost all their atoms are exposed to electrolyte. Palladium (Pd) holds great promise for catalyzing oxygen reduction reaction (ORR) but 2D Pd-based ORR catalyst has rarely been reported. Herein, 2D ternary palladium phosphoronitride (Pd3P2Nx) is synthesized, for the first time, for ORR catalysis. The synthesis is guided by a rational design using first-principles density functional theory calculations, and then realized via a postsynthesis substitutional doping of ternary palladium thiophosphate (Pd3P2S8), which almost completely replaces sulfur atoms by nitrogen atoms without destroying the 2D morphology. The doping process exposes the interlocked Pd atoms of Pd3P2S8 and introduces ligands that improve the affinity of oxygen intermediates, resulting in greater kinetics and lower activation energy for ORR. The mass activity of the pristine Pd3P2S8 is dramatically increased as much as 5-fold (from 0.03 to 0.151 mA µg-1 Pd in Pd3P2Nx). The ORR diffusion-limited current density of Pd3P2Nx (6.2 mA cm-2) exceeds that of commercial Pt/C, and it shows fast kinetics and robust long-term stability. Our theoretical calculations not only guide the experimental doping process, but also provides insights into the underlying mechanism of the outstanding ORR activity and stability.

In Situ Visualization of Lithium Penetration through Solid Electrolyte and Dead Lithium Dynamics in Solid-State Lithium Metal Batteries.

The two biggest promises of solid-state lithium (Li) metal batteries (SSLMBs) are the suppression of Li dendrites by solid-state electrolyte (SSE) and the realization of a high-energy-density Li anode. However, LMBs have not met their expectations due to Li dendrite growth causing short-circuiting. In fact, Li dendrites grow even more easily in SSE than in liquid electrolyte, but the reason for this remains unclear. Here we report in situ transmission electron microscopy observations of Li dendrite penetration through SSE and "dead" Li formation dynamics in SSLMBs. We show direct evidence that large electrochemomechanical stress generates cracks in the SSE and drives Li through the SSE directly. We revealed that fresh Li nucleation sites emerged in every discharge cycle, creating new "dead" Li in the following charging cycle and becoming the dominant Coulombic efficiency decay mechanism in SSLMBs. These results indicate that engineering flaw size and reducing electronic conductivity in SSEs are essential to improve the performance of SSLMBs.

Ultrastable Anode/Electrolyte Interface in Solid-State Lithium-Metal Batteries Using LiCux Nanowire Network Host.

High interfacial resistance and uncontrollable lithium (Li) dendrite are major challenges in solid-state Li-metal batteries (SSLMBs), as they lead to premature short-circuiting and failure of SSLMBs. Here, we report the synthesis of a composite anode comprising a three-dimensional LiCux nanowire network host infiltrated with Li (Li* anode) with low interfacial impedance and superior electrochemical performance. The Li* anode is fabricated by dissolving Cu foil into molten Li followed by solidification. The Li* anode exhibits good wettability with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and high mechanical strength, rendering low Li*/LLZTO interfacial impedance, homogeneous deposition of Li, and suppression of Li dendrites. Consequently, the Li* anode-based symmetric cells and full cells with LiNi0.88Co0.1Al0.02O2 (NCA), LiFePO4 (LFP), and FeF2 cathodes deliver remarkable electrochemical performance. Specifically, the Li*/LLZTO/Li* symmetrical cell achieves a remarkably long cycle lifetime of 10 000 h with 0.1 mA·cm-2; the Li*/LLZTO/NCA full cell maintains capacity retention of 73.4% after 500 cycles at 0.5C; and all-solid-state Li*/LLZTO/FeF2 full cell achieves a reversible capacity of 147 mAh·g-1 after 500 cycles at 100 mA·g-1. This work demonstrates potential design tactics for an ultrastable Li*/garnet interface to enable high-performance SSLMBs.

In Situ Measurements of the Mechanical Properties of Electrochemically Deposited Li2CO3 and Li2O Nanorods.

Solid-electrolyte interface (SEI) is "the most important but least understood (component) in rechargeable Li-ion batteries". The ideal SEI requires high elastic strength and can resist the penetration of a Li dendrite mechanically, which is vital for inhibiting the dendrite growth in lithium batteries. Even though Li2CO3 and Li2O are identified as the major components of SEI, their mechanical properties are not well understood. Herein, SEI-related materials such as Li2CO3 and Li2O were electrochemically deposited using an environmental transmission electron microscopy (ETEM), and their mechanical properties were assessed by in situ atomic force microscopy (AFM) and inverse finite element simulations. Both Li2CO3 and Li2O exhibit nanocrystalline structures and good plasticity. The ultimate strength of Li2CO3 ranges from 192 to 330 MPa, while that of Li2O is less than 100 MPa. These results provide a new understanding of the SEI and its related dendritic problems in lithium batteries.

Tailoring P2/P3 Biphases of Layered Nax MnO2 by Co Substitution for High-Performance Sodium-Ion Battery.

P-type layered oxide is a promising cathode candidate for sodium-ion batteries (SIBs), but faces the challenge of simultaneously realizing high rate capability and long cycle life. Herein, Co-substituted Nax MnO2 nanosheets with tunable P2/P3 biphase structures are synthesized by a novel dealloying-annealing strategy. The optimized P2/P3-Na0.67 Mn0.64 Co0.30 Al0.06 O2 cathode delivers an excellent rate capability of 83 mA h g-1 at a high current density of 1700 mA g-1 (10 C), and an outstanding cycling stability over 500 cycles at 1000 mA g-1 . This excellent performance is attributed to the unique P2/P3 biphases with stable crystal structures and fast Na+ diffusion between open prismatic Na sites. Moreover, operando X-ray diffraction is applied to explore the structural evolution of Na0.67 Mn0.64 Co0.30 Al0.06 O2 during the Na+ extraction/insertion processes, and the P2-P2' phase transition is effectively suppressed. Operando Raman technique is utilized to explore the structural superiority of P2/P3 biphase cathode compared with pure P2 or P3 phase. This work highlights precisely tailoring the phase composition as an effective strategy to design advanced cathode materials for SIBs.

Direct Growth of Polycrystalline GaN Porous Layer with Rich Nitrogen Vacancies: Application to Catalyst-Free Electrochemical Detection.

It has been demonstrated that defect engineering is an effective strategy to enhance the activity of materials. Herein, a polycrystalline GaN porous layer (PGP) with high catalytic activity was grown by self-assembly on GaN-coated sapphire substrate by using low-temperature (LT) MOCVD growth. Without doping, LT growth can significantly improve the activity and electrical conductivity of PGP, owing to the presence of rich N-vacancies (∼1020 cm-3). Identification of rich N-vacancies in the PGP material was realized by using atomically resolved STEM (AR-STEM) characterization. The optimized PGP was applied to catalyst-free electrochemical detection of H2O2 with a limit of detection (LOD) of 50 nM, a fast response speed of 3 s, a wide linear detection range (50 nM to 12 mM), and a high stability. The LOD is exceeding 40 fold lower than that of reported metal-catalyst decorated GaN. Moreover, a quantitative relationship between the sensing performances and N-vacancy of PGP was established. To our knowledge, it is the first time that intrinsic GaN materials can exhibit high catalytic activity.

In Situ Electrochemical Study of Na-O2/CO2 Batteries in an Environmental Transmission Electron Microscope.

Metal-air batteries are potential candidates for post-lithium energy storage devices due to their high theoretical energy densities. However, our understanding of the electrochemistry of metal-air batteries is still in its infancy. Herein we report in situ studies of Na-O2/CO2 (O2 and CO2 mixture) and Na-O2 batteries with either carbon nanotubes (CNTs) or Ag nanowires as the air cathode medium in an advanced aberration corrected environmental transmission electron microscope. In the Na-O2/CO2-CNT nanobattery, the discharge reactions occurred in two steps: (1) 2Na+ + 2e- + O2 → Na2O2; (2) Na2O2+ CO2 → Na2CO3 + O2; concurrently a parasitic Na plating reaction took place. The charge reaction proceeded via (3) 2Na2CO3 + C → 4Na+ + 3CO2 + 4e-. In the Na-O2/CO2-Ag nanobattery, the discharge reactions were essentially the same as those for the Na-O2/CO2-CNT nanobattery; however, the charge reaction in the former was very sluggish, suggesting that direct decomposition of Na2CO3 is difficult. In the Na-O2 battery, the discharge reaction occurred via reaction 1, but the reverse reaction was very difficult, indicating the sluggish decomposition of Na2O2. Overall the Na-O2/CO2-CNT nanobattery exhibited much better cyclability and performance than the Na-O2/CO2-Ag and the Na-O2-CNT nanobatteries, underscoring the importance of carbon and CO2 in facilitating the Na-O2 nanobatteries. Our study provides important understanding of the electrochemistry of the Na-O2/CO2 and Na-O2 nanobatteries, which may aid the development of high performance Na-O2/CO2 and Na-O2 batteries for energy storage applications.

Lithium whisker growth and stress generation in an in situ atomic force microscope-environmental transmission electron microscope set-up.

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.

Air-Stable Lithium Spheres Produced by Electrochemical Plating.

Lithium metal is an ideal anode for next-generation lithium batteries owing to its very high theoretical specific capacity of 3860 mAh g-1 but very reactive upon exposure to ambient air, rendering it difficult to handle and transport. Air-stable lithium spheres (ASLSs) were produced by electrochemical plating under CO2 atmosphere inside an advanced aberration-corrected environmental transmission electron microscope. The ASLSs exhibit a core-shell structure with a Li core and a Li2 CO3 shell. In ambient air, the ASLSs do not react with moisture and maintain their core-shell structures. Furthermore, the ASLSs can be used as anodes in lithium-ion batteries, and they exhibit similar electrochemical behavior to metallic Li, indicating that the surface Li2 CO3 layer is a good Li+ ion conductor. The air stability of the ASLSs is attributed to the surface Li2 CO3 layer, which is barely soluble in water and does not react with oxygen and nitrogen in air at room temperature, thus passivating the Li core.

In Situ Imaging the Oxygen Reduction Reactions of Solid State Na-O2 Batteries with CuO Nanowires as the Air Cathode.

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 understanding into the oxygen chemistry in the carbonless air cathode in all solid state Na-O2 batteries.