Highly Crystalline Iridium-Nickel Nanocages with Subnanopores for Acidic Bifunctional Water Splitting Electrolysis.

Developing efficient bifunctional materials is highly desirable for overall proton membrane water splitting. However, the design of iridium materials with high overall acidic water splitting activity and durability, as well as an in-depth understanding of the catalytic mechanism, is challenging. Herein, we successfully developed subnanoporous Ir3Ni ultrathin nanocages with high crystallinity as bifunctional materials for acidic water splitting. The subnanoporous shell enables Ir3Ni NCs optimized exposure of active sites. Importantly, the nickel incorporation contributes to the favorable thermodynamics of the electrocatalysis of the OER after surface reconstruction and optimized hydrogen adsorption free energy in HER electrocatalysis, which induce enhanced intrinsic activity of the acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Together, the Ir3Ni nanocages achieve 3.72 A/mgIr(η=350 mV) and 4.47 A/mgIr(η=40 mV) OER and HER mass activity, which are 18.8 times and 3.3 times higher than that of commercial IrO2 and Pt, respectively. In addition, their highly crystalline identity ensures a robust nanostructure, enabling good catalytic durability during the oxygen evolution reaction after surface oxidation. This work provides a new revenue toward the structural design and insightful understanding of metal alloy catalytic mechanisms for the bifunctional acidic water splitting electrocatalysis.

Symmetry-Induced Regulation of Pt Strain Derived from Pt3 Ga Intermetallic for Boosting Oxygen Reduction Reaction.

Pt-based fuel cell catalysts with excellent activity and stability for proton-exchange membrane fuel cells (PEMFCs) have been developed through strain regulation in recent years. Herein, this work demonstrates that symmetry-induced strain regulation of Pt surface of PtGa intermetallic compounds can greatly enhance the catalytic performance of the oxygen reduction reaction (ORR). With the strain environment varies derived from the lattice mismatch of analogous PtGa core but different symmetry, the Pt surface of the PtGa alloy and the Pt3 Ga (Pm 3 ¯ $\bar{3}$ m) precisely realize 0.58% and 2.7% compressive strain compared to the Pt3 Ga (P4/mmm). Experimental and theoretical results reveal that when the compressive stress of the Pt lattice increases, the desorption process of O* intermediates becomes accelerated, which is conducive to oxygen reduction. The Pt3 Ga (Pm 3 ¯ $\bar{3}$ m) with high symmetry and compressive Pt surface exhibit the highest mass and specific activities of 2.18 A mgPt -1 and 5.36 mA cm-2 , respectively, which are more than one order of magnitude higher than those of commercial Pt/C catalysts. This work demonstrates that material symmetry can be used to precisely modulate Pt surface stress to enhance the ORR, as well as provide a distinct platform to investigate the relationship between Pt compressibility and catalytic activity.

Layered Inorganic Silicate Aerogel Pillared by Nanoclusters for High Temperature Thermal Insulation.

Layered inorganic material, with large-area interlayer surface and interface, provides an essential material platform for constructing new configuration of functional materials. Herein, a layered material pillared with nanoclusters realizing high temperature thermal insulation performance is demonstrated for the first time. Specifically, systematic synchrotron radiation spectroscopy and finite element calculation analysis show that ZrOx nanoclusters served as "pillars" to effectively produce porous structures with enough boundary defect while maintaining the layered structure, thereby significantly reducing solid state thermal conductivity (≈0.32 W m-1  K-1 , 298-573 K). Moreover, the layered inorganic silicate material assembled aerogel also exhibits superior thermal insulation performance from room temperature (0.034 W m-1  K-1 , 298 K, air conditions) to high temperature (0.187 W m-1  K-1 , 1073 K, air conditions) and largely enhanced compressive strength (42 kPa at 80% compression), which is the best layered material-based aerogel that has achieved synergistic improvement in thermal and mechanical performance so far. Layered inorganic silicate aerogel pillared by nanoclusters will pave a new avenue for the design of advanced thermal insulation materials under extreme conditions.

Toward Highly Selective Heteroatom Dopants in Hard Carbon with Superior Lithium Storage Performance.

Hard carbons (HCs) have gained much attention for next-generation high energy density lithium-ion battery (LIB) anode candidates. However, voltage hysteresis, low rate capability, and large initial irreversible capacity severely affect their booming application. Herein, a general strategy is reported to fabricate heterogeneous atom (N/S/P/Se)-doped HC anodes with superb rate capability and cyclic stability based on a three-dimensional (3D) framework and a hierarchical porous structure. The obtained N-doped hard carbon (NHC) exhibits an excellent rate capability of 315 mA h g-1 at 10.0 A g-1 and a long-term cyclic stability of 90.3% capacity retention after 1000 cycles at 3 A g-1. Moreover, the as-constructed pouch cell delivers a high energy density of 483.8 W h kg-1 and fast charging capability. The underlying mechanisms of lithium storage are illustrated by electrochemical kinetic analysis and theoretical calculations. It is demonstrated that heteroatom doping imposes significant effects on adsorption and diffusion for Li+. The versatile strategy in this work opens an avenue for rational design of advanced carbonaceous materials with high performance for LIB applications.

Ultrafast Superfilling Construction of a Metal Artificial Interface for Long-Term Stable Zinc Anodes.

Zinc (Zn)-metal anodes are promising candidates for large-scale, highly safe energy-storage systems. However, their cycling life is associated with instability issues such as dendritic growth, corrosion, and hydrogen evolution. Introducing an artificial metal interface is expected to help overcome this challenge owing to the optimization of the absorption, nucleation, and growth of Zn2+ . In this study, an ultrafast, universal, and cost-effective superfilling approach is developed to construct a metal artificial interface decorated Zn anode in situ. Most zincophilic metals, including Sn, Cu, and Ag, can be used to construct a homogenous interface without any restrictions on the size, morphology, or curvature of the substrates. With Sn as a proof-of-concept demonstration, the as-obtained Sn@Zn anode is conducive for the homogenous Zn nuclei and 2D diffusion of Zn2+ ions. Symmetric cells with Sn@Zn electrodes can be operated for over 900 h at different current densities. This superior performance contributes to the attractive electrochemical characteristics of both coin and scaled-up Sn@Zn//ß-MnO2 cells. Given the facile and cost-effective fabrication and recyclability of the cells, this work enables the efficient design and exploration of Zn anodes for research, industrialization, and commercialization purposes.

Ultrasmall Co3O4 nanoparticles as a long-lived high-rate lithium-ion battery anode.

Herein, ultrasmall nanostructured Co3O4 particles have been prepared by a facile two-step synthetic method and furthermore applied to lithium-ion batteries. Benefitting from an increased specific surface area and improved tolerance for volume expansion, they deliver an extremely high specific capacity of 1432.7 mA h g-1 at 0.1 A g-1 and an outstandingly long cycle life with about 511.2 mA h g-1 at 10 A g-1 after 2000 cycles. This work will pave a new way to engineer advanced electrode materials for long-lived high-rate lithium-ion batteries.

Crystalline Order Propagates Across Thick Layers of Water in Solutions of Supramolecular Nanotubes.

3D crystalline order with 1 nm resolution is observed in aqueous solutions of supramolecular nanotubes containing 94 % water, at concentrations as low as 6 wt%. 50 of star-like organic ions arrange into supramolecular rings which, in turn, stack on top of each other to form long hollow tubes with 15 nm outer diameter. Cryo-TEM and X-ray diffraction show that the parallel nanotubes arrange on a perfect hexagonal lattice. Unexpectedly, fiber diffraction on sheared solutions revealed numerous hkl Bragg reflections on several layer lines indicating longitudinal interlock between the tubes and 3D crystalline order with molecular-scale details transferred across 10 nm thick layers of water. The observed high 3D order is attributed to long-range attraction between like-charged tubes and amplified charge modulation by the extremely high intra-tube correlation length.

Surface Anion Promotes Pt Electrocatalysts with High CO Tolerance in Fuel-Cell Performance.

Platinum reaches considerable activity and stability as an electrocatalyst but is not always capable of maintaining such performance under CO poisoning, particularly in CO residual fuels for practical proton-exchange membrane fuel cells (PEMFCs). In this work, we report that surface anions including a series of nonmetal elements on Pt nanoparticles result in outstanding CO tolerance for electrocatalysts in fuel cells. In particular, phosphorus surface-anion-modified Pt (denoted as P-Pt) possesses more than 10-fold enhancement of CO tolerance (only 8.4% decay) than commercial Pt/C, which can serve as a robust electrocatalyst both in CO poisoning half cells and full cells. Moreover, the general mechanism and principle were proposed, stating that surface anions should be selected preferentially to offer electron feedback to downshift the d-band center for the Pt surface, successfully weakening CO adsorption and leading to high-tolerance capability. We anticipate that surface anions on a Pt surface can bring robust electrocatalysts for practical PEMFCs and offer novel insights for high-performance Pt-based electrocatalysts.

Directional Manipulation of Electron Transfer by Energy Level Engineering for Efficient Cathodic Oxygen Reduction.

Electron transfer plays an important role in determining the energy conversion efficiency of energy devices. Nitrogen-coordinated single metal sites (M-N4) materials as electrocatalysts have exhibited great potential in devices. However, there are still great difficulties in how to directionally manipulate electron transfer in M-N4 catalysts for higher efficiency. Herein, we demonstrated the mechanism of electron transfer being affected by energy level structure based on classical iron phthalocyanine (FePc) molecule/carbon models and proposed an energy level engineering strategy to manipulate electron transfer, preparing high-performance ORR catalysts. Engineering molecular energy level via modulating FePc molecular structure with nitro induces a strong interfacial electronic coupling and efficient charge transfer from carbon to FePc-ß-NO2 molecule. Consequently, the assembled zinc-air battery exhibits ultrahigh performance which is superior to most of M-N4 catalysts. Energy level engineering provides a universal approach for directionally manipulating electron transfer, bringing a new concept to design efficient and stable M-N4 electrocatalyst.

N-Doped hollow Fe0.4Co0.6S2@NC nanoboxes derived from a Prussian blue analogue as a sodium ion anode.

Herein, a bimetallic sulfide Fe0.4Co0.6S2@NC nanobox was prepared via a simple two-step synthetic route. The N-doped carbon coated hollow nanobox was derived from a Prussian blue analogue (PBA) and applied for an SIB anode. As expected, it exhibits a high capacity (486.6 mA h g-1 at 0.1 A g-1) and displays an excellent cycling stability (230 mA h g-1 at 10 A g-1 after 900 cycles).

Epitaxial Growth of Ultrathin Highly Crystalline Pt-Ni Nanostructure on a Metal Carbide Template for Efficient Oxygen Reduction Reaction.

Structure engineering strategies such as core-shell and hollow nanostructures are effective pathways to improve the utilization of noble metals for catalysis. However, nowadays materials design based on these strategies still largely rely on precious metal templates. Herein, the epitaxial growth of highly crystalline Pt3 Ni overlayer on earth-abundant nickel carbide is reported, forming Ni3 C@Pt3 Ni core-shell nanoparticles with a well-defined interface through a new lattice-match-directed synthetic strategy. Derived from such core-shell nanostructures, ultrathin highly crystalline Pt3 Ni nanocages have an advantageous configuration of oxygen reduction reaction (ORR)-favored facets and inherently high active surface area for the ORR, bringing high mass activity and specific activity as much as 4.71 A mgPt -1 and 5.14 mA cm-2 , which are 26 and 20 times to that of commercial Pt/C, respectively. This novel epitaxial growth of platinum opens up new avenues to rationally design highly active and economical electrocatalysts.

In Situ Architecting Endogenous Heterojunction of MoS2 Coupling with Mo2 CTx MXenes for Optimized Li+ Storage.

Endogenous heterojunction of 2D MXenes with unique structure shows inspiring potential in energy applications, which is impeded by complex synthesis method and finite MAX materials. Herein, an in situ hydrothermal strategy is implemented to successfully synthesize unique endogenous hetero-MXenes of amorphous MoS2 coupling with fluoride-free Mo2 CTx (hetero-Mo2 C) directly from Mo2 Ga2 C MAX. The distinctive morphology and heterojunction structure caused by the introduction of MoS2 endow the hetero-MXenes with extraordinary structural stability and optimized Li+ storage mechanism with improved charge transport and lithium ion adsorption capabilities. As a result, hetero-Mo2 C exhibits excellent electrochemical performance with a high discharge specific capacity of 1242 mAh g-1 at 0.1 A g-1 and long cycle stability of 683.9 mAh g-1 after 1200 cycling. This work provides new insights into rational design of novel MXenes heterojunctions, practically important for the development of MXenes and their applications in high-performance energy storage systems.

Sub-2 nm Ultrasmall High-Entropy Alloy Nanoparticles for Extremely Superior Electrocatalytic Hydrogen Evolution.

The development of sufficiently effective catalysts with extremely superior performance for electrocatalytic hydrogen production still remains a formidable challenge, especially in acidic media. Here, we report ultrasmall high-entropy alloy (us-HEA) nanoparticles (NPs) with the best-level performance for hydrogen evolution reaction (HER). The us-HEA (NiCoFePtRh) NPs show an average diameter of 1.68 nm, which is the smallest size in the reported HEAs. The atomic structure, coordinational structure, and electronic structure of the us-HEAs were comprehensively clarified. The us-HEA/C achieves an ultrahigh mass activity of 28.3 A mg-1noble metals at -0.05 V (vs the reversible hydrogen electrode, RHE) for HER in 0.5 M H2SO4 solution, which is 40.4 and 74.5 times higher than those of the commercial Pt/C and Rh/C catalysts, respectively. Moreover, the us-HEA/C demonstrates an ultrahigh turnover frequency of 30.1 s-1 at 50 mV overpotential (41.8 times higher than that of the Pt/C catalyst) and excellent stability with no decay after 10 000 cycles. Operando X-ray absorption spectroscopy and theoretical calculations reveal the actual active sites, tunable electronic structures, and a synergistic effect among five elements, which endow significantly enhanced HER activity. This work not only engineers a general and scalable strategy for synthesizing us-HEA NPs and elucidates the complex structural information and catalytic mechanisms of multielement HEA system in depth, but also highlights HEAs as sufficiently advanced catalysts and accelerates the research of HEAs in energy-related applications.

Structural Transformation of Heterogeneous Materials for Electrocatalytic Oxygen Evolution Reaction.

Electrochemical water splitting for hydrogen generation is a promising pathway for renewable energy conversion and storage. One of the most important issues for efficient water splitting is to develop cost-effective and highly efficient electrocatalysts to drive sluggish oxygen-evolution reaction (OER) at the anode side. Notably, structural transformation such as surface oxidation of metals or metal nonoxide compounds and surface amorphization of some metal oxides during OER have attracted growing attention in recent years. The investigation of structural transformation in OER will contribute to the in-depth understanding of accurate catalytic mechanisms and will finally benefit the rational design of catalytic materials with high activity. In this Review, we provide an overview of heterogeneous materials with obvious structural transformation during OER electrocatalysis. To gain insight into the essence of structural transformation, we summarize the driving forces and critical factors that affect the transformation process. In addition, advanced techniques that are used to probe chemical states and atomic structures of transformed surfaces are also introduced. We then discuss the structure of active species and the relationship between catalytic performance and structural properties of transformed materials. Finally, the challenges and prospects of heterogeneous OER electrocatalysis are presented.

Subsize Pt-based intermetallic compound enables long-term cyclic mass activity for fuel-cell oxygen reduction.

Pt-based alloy catalysts may promise considerable mass activity (MA) for oxygen reduction but are generally unsustainable over long-term cycles, particularly in practical proton exchange membrane fuel cells (PEMFCs). Herein, we report a series of Pt-based intermetallic compounds (Pt3Co, PtCo, and Pt3Ti) enclosed by ultrathin Pt skin with an average particle size down to about 2.3 nm, which deliver outstanding cyclic MA and durability for oxygen reduction. By breaking size limitation during ordered atomic transformation in Pt alloy systems, the MA and durability of subsize Pt-based intermetallic compounds can be simultaneously optimized. The subsize scale was also found to enhance the stability of the membrane electrode through preventing the poisoning of catalysts by ionomers in humid fuel-cell conditions. We anticipate that subsize Pt-based intermetallic compounds set a good example for the rational design of high-performance oxygen reduction electrocatalysts for PEMFCs. Furthermore, the prevention of ionomer poisoning was identified as the critical parameter for assembling robust commercial membrane electrodes in PEMFCs.

Intrinsic Room-Temperature Ferromagnetism in V2C MXene Nanosheets.

Two-dimensional (2D) materials with intrinsic magnetic properties are intensively explored due to their potential applications in low-power-consumption electronics and spintronics. To date, only a handful of intrinsic magnetic 2D materials have been reported. Here, we report a realization of intrinsic ferromagnetic behavior in 2D V2C MXene nanosheets through layer mismatch engineering. The V2C MXene nanosheets with a small-angle twisting show a robust intrinsic ferromagnetic response with a saturation magnetic moment of 0.013 emu/g at room temperature. An in-depth study has been performed by X-ray absorption spectroscopy as well as electron paramagnetic resonance (EPR) and photoelectron spectroscopy analyses. It has been revealed that the symmetry-broken interlayer twisting reduced the degeneracy of V 3d states and the van Hove singularity. This led to a redistribution of the density of electronic states near the Fermi level and consequently activated the Stoner ferromagnetism with improved density of itinerant d electrons. This work highlights V2C MXene as a promising intrinsic room-temperature ferromagnetic material with potential applications in spintronics or spin-based electronics.

Rational design of hierarchical FeSe2 encapsulated with bifunctional carbon cuboids as an advanced anode for sodium-ion batteries.

Earth-abundant transition-metal selenides (TMSs) have aroused great interest towards their application in sodium-ion batteries (SIBs). Herein, we present Fe-based Prussian blue analogs (PBA) modified by graphene oxide as precursors to synthesize FeSe2 nanoparticles within a nitrogen-doped carbon (NC) matrix and graphene layer (FeSe2/NC@G). The bifunctional carbon wrapped FeSe2/NC@G shows excellent sodium-storage performance with a large reversible capacity of 331 mA h g-1 at 5.0 A g-1 and a high cyclability of 323 mA h g-1 at the current density of 2.0 A g-1 after 1000 cycles (82% capacity retention). Furthermore, full SIBs are also fabricated and exhibit superior capacities and stabilities. The remarkable electrochemical properties result from the formation of an Fe-O-C chemical bond in the composite with enhanced electronic/ionic diffusion kinetics and structural integrity. This study paves the way for the successful synthesis of novel nanostructural TMSs which can be utilized in energy storage system application.

Inhibition of oxygen dimerization by local symmetry tuning in Li-rich layered oxides for improved stability.

Li-rich layered oxide cathode materials show high capacities in lithium-ion batteries owing to the contribution of the oxygen redox reaction. However, structural accommodation of this reaction usually results in O-O dimerization, leading to oxygen release and poor electrochemical performance. In this study, we propose a new structural response mechanism inhibiting O-O dimerization for the oxygen redox reaction by tuning the local symmetry around the oxygen ions. Compared with regular Li2RuO3, the structural response of the as-prepared local-symmetry-tuned Li2RuO3 to the oxygen redox reaction involves the telescopic O-Ru-O configuration rather than O-O dimerization, which inhibits oxygen release, enabling significantly enhanced cycling stability and negligible voltage decay. This discovery of the new structural response mechanism for the oxygen redox reaction will provide a new scope for the strategy of enhancing the anionic redox stability, paving unexplored pathways toward further development of high capacity Li-rich layered oxides.

Nanopore Confinement of Electrocatalysts Optimizing Triple Transport for an Ultrahigh-Power-Density Zinc-Air Fuel Cell with Robust Stability.

Metal-air fuel cells with high energy density, eco-friendliness, and low cost bring significantly high security to future power systems. However, the impending challenges of low power density and high-current-density stability limit their widespread applications. In this study, an ultrahigh-power-density Zn-air fuel cell with robust stability is highlighted. Benefiting from the water-resistance effect of the confined nanopores, the highly active cobalt cluster electrocatalysts reside in specific nanopores and possess stable triple-phase reaction areas, leading to the synergistic optimization of electron conduction, oxygen gas diffusion, and ion transport for electrocatalysis. As a result, the as-established Zn-air fuel cell shows the best stability under high-current-density discharging (>90 h at 100 mA cm-2 ) and superior power density (peak power density: >300 mW cm-2 , specific power: 500 Wgcat -1 ) compared to most reported non-noble-metal electrocatalysts. The findings will provide new insights in the rational design of electrocatalysts for advanced metal-air fuel cell systems.

Surface Nitrogen-Injection Engineering for High Formation Rate of CO2 Reduction to Formate.

In this study, we highlight that surface nitrogen-injection engineering brings a high formation rate for CO2 reduction to formate, which is high level among the reported electrocatalysts. Surface nitrogen-injection engineering can increase the amounts of active sites and optimize the electronic structure simultaneously. Taking an example of SnS2 precursors, the final-obtained surface N-enriched Sn(S) nanosheets (denoted as N-Sn(S) nanosheets) exhibit a 5-fold of current density and 2.45-fold of Faradaic efficiency than pristine SnS2 derived Sn(S) nanosheets (denoted as Sn(S) nanosheets). On account of high activity and selectivity, the formation rate of formate is 14 times than that of pristine samples and reaches up to 1358 µmol h-1 cm-2. Moreover, this strategy is proven to be general to other metal sulfides, such as CuS and In2S3. We anticipate that surface nitrogen-injection engineering offers new avenues to rational design of advanced electrocatalysts for CO2 reduction reaction.