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Fabricating highly efficient and robust oxygen reduction reaction (ORR) electrocatalysts is challenging but desirable for practical Zn-air batteries. As an early transition-metal oxide, zirconium dioxide (ZrO2) has emerged as an interesting catalyst owing to its unique characteristics of high stability, anti-toxicity, good catalytic activity, and small oxygen adsorption enthalpies. However, its intrinsically poor electrical conductivity makes it difficult to serve as an ORR electrocatalyst. Herein, we report ultrafine N-doped ZrO2 nanoparticles embedded in an N-doped porous carbon matrix as an ORR electrocatalyst (N-ZrO2/NC). The N-ZrO2/NC catalyst displays excellent activity and long-term durability with a half-wave potential (E1/2) of 0.84 V and a selectivity for the four-electron reduction of oxygen in 0.1 M KOH. Upon employment in a Zn-air battery, N-ZrO2/NC presented an intriguing power density of 185.9 mW cm−2 and a high specific capacity of 797.9 mA h gZn−1, exceeding those of commercial Pt/C (122.1 mW cm−2 and 782.5 mA h gZn−1). This excellent performance is mainly attributed to the ultrafine ZrO2 nanoparticles, the conductive carbon substrate, and the modified electronic band structure of ZrO2 after N-doping. Density functional theory calculations demonstrated that N-doping can reduce the band-gap of ZrO2 from 3.96 eV to 3.33 eV through the hybridization of the p state of the N atom with the 2p state of the oxygen atom; this provides enhanced electrical conductivity and results in faster electron-transfer kinetics. This work provides a new approach for the design of other enhanced semiconductor and insulator materials.

Aqueous zinc-ion batteries (ZIBs) have attracted great attention as the candidates for large-scale energy storage system, recently, because of their low cost, environment-friendly, high safety, and high theoretical energy densities. Among the numerous cathode materials, layered structure vanadium based polyanionic compounds, such as VOPO4, exhibit high specific capacity for Zn ion storage. However, the low Zn ion diffusion coefficient and limited interlayer spacing make the cathodes low reversible capacity and inferior cycling stability. Herein, K ions were pre-intercalated into the VOPO4 layers via ions exchange adopting VOPO4•2H2O as the precursor. When evaluated as the cathode for ZIBs, an excellent cycle stability of 400 cycles under a current density of 500 mA g−1 was achieved by the obtained KVOPO4 electrode, verifying the positive effect of intercalation engineering. Furtherly, a solid-solution reaction Zn ion storage mechanism was confirmed. This study provides a new insight to explore high performance cathode materials for ZIBs.

Bimetallic sulfides display good electroconductibility and more redox active sites for sodium ion storage, which are expected to realize fast charging/discharging of sodium ion hybrid capacitors (SIHCs) integration. Herein, Sb was introduced into SnS2 on graphene (ATS/GNS) to enhance the kinetics of Na+ storage. The introduction of Sb at Sn site in SnS2 leads to a residual delocalized s electron and forms a half-filled and delocalized intermediate band, which can effectively improve electroconductivity. ATS possesses a high adsorption energy (-3.13 eV) and low diffusion energy barrier (0.26 eV) of Na+ by density functional theory calculations. ATS/GNS with remarkable stability possesses a reversible capacity of 507 mAh g−1 at 1 A g−1 after 3000 cycles. The ATS/GNS//N, S doped porous carbon SIHC delivers high energy/power densities (115 Wh kg−1/351 W kg−1 and 41 Wh kg−1/18750 W kg−1), and an excellent capacity retention of 70% after 10000 cycles at 5 A g−1. This work may present a feasible approach to design high-rate and long-term stability of sodium-based devices.

Main-group (s- and p-block) metals are generally regarded as catalytically inactive due to the delocalized s/p-band. Herein, we successfully synthesized a p-block antimony single-atom catalyst (Sb SAC) with the Sb-N4 configuration for efficient catalysis of the oxygen reduction reaction (ORR). The obtained Sb SAC exhibits superior ORR activity with a half-wave potential of 0.86 V and excellent stability, which outperforms most transition-metal (TM, d-block) based SACs and commercial Pt/C. In addition, it presents an excellent power density of 184.6 mW cm-2 and a high specific capacity (803.5 mAh g-1 ) in Zn-air battery. Both experiment and theoretical calculation manifest that the active catalytic sites are positively charged Sb-N4 single-metal sites, which have closed d shells. Density of states (DOS) results unveil the p orbital of the atomically dispersed Sb cation in Sb SAC can easily interact with O2 -p orbital to form hybrid states, facilitating the charge transfer and generating appropriate adsorption strength for oxygen intermediates, lowering the energy barrier and modulating the rate-determining step. This work sheds light on the atomic-level preparing p-block Sb metal catalyst for highly active ORR, and further provides valuable guidelines for the rational design of other main-group-metal SACs.

The lower energy density and safety issues of liquid sodium-ion batteries have been unable to satisfy the ever-increasing demands for large-scale energy storage system. As a low-cost alternative, s...

Electrochemical water splitting is a fascinating technology for sustainable hydrogen production, and electrocatalysts are essential to accelerate the sluggish hydrogen and oxygen evolution reactions (HER and OER). Transition-metal-based electrocatalysts have attracted enormous interests due to the abundant resources, low cost, and comparable catalytic performance to noble metals. Among these studies, fibrous materials possess distinct advantages, such as unique structure, high active surface area, and fast electron transport. Herein, the most recent progress of nanofiber electrocatalysts on synthesis and application in HER and OER is summarized, with emphasis on iron-, cobalt-, and nickel-based materials. Moreover, the challenge and prospects of fibrous-structured electrocatalysts on water splitting is provided.

The intrinsically sluggish kinetics of the anodic oxygen evolution reaction (OER) is deemed to be the bottleneck for highly efficient electrocatalytic hydrogen production, and the by-product is less value-added oxygen. Herein, we report rational construction of Mo doped Co4N nanoarrays (Mo-Co4N) with an open skeleton structure as a robust bifunctional electrocatalyst for concurrent electrolytic high-purity hydrogen and value-added formate productions in the cathodic and anodic process. Benefitting from Mo doping, the unique structure characteristics of more exposed active sites, and optimized electronic synergy, Mo-Co4N exhibits intriguing hydrogen evolution reaction (HER) activity with an exceptionally small overpotential of 45 mV at 10 mA cm−2 and a low Tafel slope of 42 mV dec−1. Meanwhile, when the anodic partial methanol oxidation reaction (MOR) is used to replace the OER, the oxidation potential is significantly reduced to 1.356 V at 10 mA cm−2. In particular, a two-electrode electrolyzer employing Mo-Co4N as a bifunctional catalyst only requires an ultralow cell voltage of 1.427 V to achieve a current density of 10 mA cm−2, featuring low energy consumption in comparison to traditional overall water splitting. Furthermore, high Faraday efficiencies approaching 100% for hydrogen evolution and value-added formate production are achieved, as well as excellent 60 h long-term durability.

The interfacial instability between Ni-rich layered oxide cathodes and sulfide electrolytes is a serious problem, leading to poor electrochemical properties of all-solid-state lithium batteries (ASSLB). The chemical/electrochemical side reactions are considered to be the origin of the interfacial deterioration. However, the influence of chemical and electrochemical side reactions on the interfacial deterioration is rarely studied specifically. In this work, the deterioration mechanism of the interface between LiNi0.85-xCo0.15AlxO2 and Li10GeP2S12 is investigated in detail by combining in/ex-situ Raman spectra and Electrochemical Impedance Spectroscopy (EIS). It can be determined that chemical side reaction between LiNi0.8Co0.15Al0.05O2 and Li10GeP2S12 will occur immediately once contacted, and the interfacial deterioration becomes more serious after charge-discharge process under the dual effects of chemical and electrochemical side reactions. Moreover, our research reveals that the interfacial stability and the cycle performance of ASSLB can be greatly enhanced by increasing Al-substitution for Ni in LiNi0.85-xCo0.15AlxO2. In particular, the capacity retention of LiNi0.6Co0.15Al0.25O2 cathode after 200 cycles can reach 81.9%, much higher than that of LiNi0.8Co0.15Al0.05O2 cathode (12.5%@200 cycles). This work gives an insight to study the interfacial issues between Ni-rich layered oxide cathode and sulfide electrolyte for ASSLBs.

P2-type layered oxides suffer from an ordered Na+ /vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na+ extraction/insertion. The deficient sodium in the P2-type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na+ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau-free P2-type cathode-Na0.85 Li0.12 Ni0.22 Mn0.66 O2 (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na+ mobility (10-11 to 10-10 cm2 s-1 ) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g-1 , superior rate capability of 79.3 mA h g-1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realizing high-performance P2-type cathodes for sodium-ion batteries.

The sodium super ionic conductor (NASICON) structured Na3MnTi(PO4)3 is attractive due to the eco-friendly and low-cost Na–Mn–Ti–P–O system. However, Na3MnTi(PO4)3 suffers from low Coulombic efficiency, inferior electronic conductivity and limited specific capacity basing on two-sodium-exchange. To address these multifaceted issues, herein, an interpenetrating graphene encapsulated Na3MnTi(PO4)3 particles with carbon-shell covering material (rGO@NMTP-C) was synthesized. By regulating cut-off voltages, a three-electron reaction was realized and Coulombic efficiency of the rGO@NMTP-C was found to increase from

To realize high-rate and long-term performance of rechargeable batteries, the most effective approach is to develop an advanced hybrid material with a stable structure and more reaction active sites. Recently, 2D MXenes have become an up-and-coming electrode owing to their high conductivity and large redox-active surface area. In this work, we firstly prepared Ti3C2 MXenes through the selective etching of silicon from Ti3SiC2 (MAX) using HF and an oxidant for highly durable lithium-ion batteries (LIBs). The interlayer distance of Ti3C2 MXenes can be controlled with the oxidizability of the oxidant and etching temperature. In addition, Ti3C2@TiO2 MXene hybrids with further expanded interlayer spacing were purposefully fabricated by a simple hydrothermal method. The hierarchical N-doped Ti3C2@TiO2 MXene hybrids show that the in situ synthesized nanoscale TiO2 particles are loaded homogeneously on the layered N-doped Ti3C2 surface. The interlayer distance of N-doped Ti3C2@TiO2 MXene can reach 12.77 A when using HNO3 as the oxidant at room temperature. As an anode material, the N-doped Ti3C2@TiO2(HNO3-RT) hybrid displays a high reversible capacity of 302 mA h g−1 at 200 mA g−1 after 500 cycles and 154 mA h g−1 at 2000 mA g−1 after 1500 cycles, which indicates its long cycle lifetime and excellent stability in LIBs. This highly durable LIB anode performance is ascribed to synergetic contributions from the high capacitive contribution, high electrical conductivity, high-capacity of in situ formed nanoscale TiO2 and interlayer-expanded architecture of the N-doped Ti3C2@TiO2(HNO3-RT). This study provides a theoretical basis for the application of MXenes as high capacity anodes for advanced LIBs.

Aqueous alkali ion batteries attract increasing attention due to their merits of being safety, eco-friendly and low cost. Nevertheless, their development is hindered by the lack of suitable electrode materials with high capacity and cycling stability. As promising candidates, Prussian blue and its analogues (PBAs) are particularly attractive cathode materials in the energy storage field for their excellent electrochemical properties. Co-based PBAs (CoHCF) have relatively high discharge plateau, high theoretical capacity and good cycle performance. The potassium storage mechanism of CoHCF is still unclear and lacks study. Herein, a novel low-defect CoHCF was synthesized by a feasible coprecipitation method. When applied in aqueous potassium ion batteries (AKIBs), the two-electron-transfer process is observed clearly. The CoHCF electrode delivers a high reversible capacity of 83.6 mA h g−1 at a current density of 20 mA g−1 after 200 cycles. In addition, excellent rate performance and long cycling stability at 600 mA g−1 were obtained. The structural evolution and reaction mechanism of CoHCF upon K+ extraction/insertion were visibly characterized by ex situ X-ray diffraction and X-ray photoelectron spectroscopies. The results demonstrate a new strategy for the development of AKIB cathodes with excellent electrochemical performance.

Metallic antimony (Sb) is an attractive anode material for lithium-/sodium-ion batteries (LIBs/SIBs) because of its high theoretical capacity (660 mA h g–1), but it suffers from poor cycling performance caused by the huge volume expansion and the unstable solid electrolyte interphase (SEI). Here, we report a high-performing microsized Sb anode for both LIBs and SIBs by coupling it with fluoroethylene carbonate (FEC) containing electrolytes. The optimum amount of FEC (10 vol %) renders a stable LiF/NaF-rich SEI on Sb electrodes that can suppress the continuous electrolyte decomposition and accommodate the volume variation. The microsized Sb electrode gradually evolves into a porous integrity assembled by nanoparticles in FEC-containing electrolytes during cycling, which is totally different from that in the FEC-free counterpart. As a result, the microsized Sb electrodes exhibit a reversible capacity of 540 mA h g–1 with 85.3% capacity retention after 150 cycles at 1000 mA g–1 for LIBs and 605 mA h g–1 with...

In an attempt to develop low-cost, non-noble-metal bifunctional electrocatalysts for water elec-trolysis in alkaline media, cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate. Benefiting from the optimized electronic structure and enhanced mass and charge transport, as well as the 3D conducting pathway, MoxCoy@N-CNS /CNT shows superior performance towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. The optimal electrocatalyst is Mo2Co1@N-CNS /CNT , which reveals a current density of 10 mA cm-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER, respectively, and a relatively low cell voltage (1.63 V) for the overall water electrolysis. The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.

Sn is considered as a promising anode for lithium-ion batteries due to its low cost and high theoretical capacity (992 mA h g −1 with Li4.4Sn). However, the volume expansion (∼300%) during lithiation/delithiation process can result in the continuous pulverization of active materials and exfoliation from current collector, deteriorating the capacity and cycling performance. Here Co/Co3SnC0.7 N-doped carbon nanofibers are successfully synthesized by a feasible electrospinning method. And the materials as the self-standing anode for lithium-ion batteries reveal a high-rate performance as delivering reversible capacities of 480 mA h g−1 at 100 mA g−1 and 290 mA h g−1 at 2000 mA g−1. In addition, the specific capacity can still maintain 320 mA h g−1 at 500 mA g−1 even after 900 cycles, showing the outstanding cycling stability. The inactive metal Co and one-dimensional N-doped carbon nanofibers synergistically promote the electrochemical performance of the Sn-based anode by inhibiting the aggregation of the nanoparticles and buffering volume variation during lithiation/delithiation process.

Rechargeable lithium metal batteries (LMBs) are considered as promising candidates for high-energy storage systems, but their practical applications are plagued by the severe safety concerns and poor cyclability. Here we report a fire-retardant electrolyte consisting of 2.8 M lithium bis(trifluoromethanesulfonyl)imide in triethyl phosphate (TEP) with 10 vol % fluoroethylene carbonate (FEC) for high-performance LMBs. This concentrated system with almost no free solvent molecules and anions can alleviate the electrolyte reactivity toward Li anode and improve the anodic stability up to 5.0 V. FEC cosolvents as functional additives can enhance the ionic conductivity and reduce the viscosity of the concentrated electrolyte. Moreover, the presence of FEC in the TEP-based electrolyte favors to form a stable LiF-rich solid electrolyte interphase, suppressing the parasitic reactions between Li and TEP solvent and enabling a dendrite-free cycling of Li anode. A Li||LiFePO4 battery using this electrolyte shows a hig...

Developing low-cost and highly efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is attractive for overall water splitting. Herein, we firstly use the globally generated green cornstalks as the carbon source to prepare highly efficient bifunctional pure β-phase molybdenum carbide (β-Mo2C) electrocatalysts. Due to the highly intrinsic activity of β-Mo2C, high porosity of the resultant and synergistic effect between the Mo2C and carbon matrix, the as-prepared catalyst exhibits excellent electrocatalytic activities with low overpotentials of 130 mV and 274 mV to achieve a current density of 10 mA cm−2 for the HER and OER, respectively. As a bifunctional electrocatalyst for overall water splitting, the electrolyzer only needs a cell voltage of 1.65 V at 10 mA cm−2 in alkaline water, as well as long-term stability of 30 h. This intriguing preparation strategy will open up an exciting new avenue for the synthesis of other carbides.

Sn is a promising anode material for lithium-ion batteries (LIBs). However, the huge volume changes during lithiation/delithiation processes lead to the pulverization of electrodes, thus resulting in poor cycling stability and rate performance. An N-doped microporous carbon matrix (N-MCM) derived from ZIF-8 with highly porous structures and open frameworks can effectively buffer volume expansion, restrain the aggregation of Sn nanoparticles and accelerate the diffusion of electrons/Li ions, contributing to the improvement of the electrochemical performance. Herein, we firstly used a facile chemical vapor transformation (CVT) method to confine Sn (∼0.8 nm) in an N-doped microporous carbon matrix (Sn@N-MCM). The as-prepared Sn@N-MCM as an anode for LIBs displays a high specific capacity (814.3 mA h g−1 at 0.1 A g−1), an excellent rate capability (225.5 mA h g−1 even at 20 A g−1), and an outstanding cycling stability (470 mA h g−1 after 2500 cycles at 4 A g−1). This work may open up a new avenue to design energy storage materials by utilizing the facile CVT method.

Na2MnP2O7 has been considered as a promising cathode candidate for advanced sodium-ion batteries due to its high potential, low cost and non-toxicity. However, the low initial Coulombic efficiency, poor high-rate and unsatisfactory cycling ability originated from the intrinsic inferior electronic conductivity and manganese dissolution severely hinder its practical application. Herein, we report an approach based on a feasible high energy vibrating activation process to fabricate a robust graphene layers (GL) modified Na2MnP2O7 material (noted as NMP@GL) for the first time. The as-prepared NMP@GL could exhibit an ultrahigh initial Coulombic efficiency of 90%, and a high energy density over 300 Wh kg-1. In addition, rate performance and cycling stability were also improved, with high capacity retention of 83% after 600 cycles at 2 C. These impressive progresses should be ascribed to the enhanced electron transportation with distinctive framework through graphene layer modifying, and structural stability of triclinic Na2MnP2O7 with spacious 3D ion migration channels. Ex-situ XRD and GITT demonstrate a consecutive multi-phase reaction mechanism with facile sodium diffusion. Our design makes Na2MnP2O7@GL to achieve its potential for practical application.

Electrochemical devices, as renewable and clean energy systems, display a great potential to meet the sustainable development in the future. However, well-designed and highly efficient electrocatalysts are the technological dilemmas that retard their practical applications. Metal-organic frameworks (MOFs) derived electrocatalysts exhibit tunable structure and intriguing activity and have received intensive investigation in recent years. In this review, the recent progress of MOFs-derived carbon-based single atoms (SAs) and metal nanoparticles (NPs) catalysts for energy-related electrocatalysis is summarized. The effects of synthesis strategy, coordination environment, morphology, and composition on the catalytic activity are highlighted. Furthermore, these SAs and metal NPs catalysts for the applications of electrocatalysis (hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction) are overviewed. Finally, some current challenges and foresighted ideas for MOFs-derived carbon-based metal electrocatalysts are presented.

Room-temperature sodium-ion batteries (SIBs) are regarded as promising candidates for smart grids and large-scale energy storage systems (EESs) due to their significant benefits of abundant and low-cost sodium resource. Among the previously reported cathode materials for SIBs, layered transition-metal oxides and polyanion-type materials are considered to be the most attractive options. Although many layered transition-metal oxides can provide high capacity due to their small molecular weight, their further application is hindered by low output voltage (mostly lower than 3.5 V), irreversible phase transition as well as storage instability. Comparatively, polyanion-type materials exhibit higher operating potentials due to the inductive effect of polyanion groups. Their robust 3D framework significantly decreases the structural variations during sodium ion de/intercalation. Moreover, the effect of strong X-O (X = S, P, Si, etc.) covalent bonds can effectively inhibit oxygen evolution. These advantages contribute to the superior cycle stability and high safety of polyanion-type materials. However, low electronic conductivity and limited capacity still restrict their further application. This review summarizes the recent progress of polyanion-type materials for SIBs, which include phosphates, fluorophosphates, pyrophosphates, mixed phosphates, sulfates, and silicates. We also discuss the remaining challenges and corresponding strategies for polyanion-type materials. We hope this review can provide some insights into the development of polyanionic materials.

Designing the hydrogen evolution reaction (HER) electrocatalysts by tuning the micro/nano structure and optimizing composition to overcome the sluggish HER kinetics have fueled intensive research interests in recent years. Herein, the Co and CoP nanograins embedded in porous nitrogen-doped carbon nanofibers (Co/CoP@NC) are prepared by a controllable electrospinning method and subsequent thermal treatments as the wide-pH HER electrocatalysts. Owning to the prominent merits of strong synergistic relationships between Co and CoP nanoparticles, N-doped carbon configuration, and the interconnected three dimensional (3D) porous carbon network, the Co/CoP@NC nanofibers exhibit robust HER activity with affording an overpotential of 117 mV in acidic and 180 mV in alkaline media to deliver the current density of 10 mA cm-2. As a practical application, when integrated the Co/CoP@NC/Ni foam cathode with the NiFe layered double hydroxides/Ni foam anode (NiFe-LDH/Ni foam), the electrolyzer can afford the cell voltage of 1.62 V to deliver the current density of 10 mA cm-2, as well as ultralong lifetime of 60 h in alkaline medium, providing a viable alternative to the noble-metal electrocatalysts for water splitting.

Lithium alanate (LiAlH4 ) is of particular interest as one of the most promising candidates for solid-state hydrogen storage. Unfortunately, high dehydrogenation temperatures and relatively slow kinetics limit its practical applications. Herein, 3D flower-like nanocrystalline Ni/C, composed of highly dispersed Ni nanoparticles and interlaced carbon flakes, was synthesized in situ. The as-synthesized nanocrystalline Ni/C significantly decreased the dehydrogenation temperature and dramatically improved the dehydrogenation kinetics of LiAlH4 . It was found that the LiAlH4 sample with 10 wt % Ni/C (LiAlH4 -10 wt %Ni/C) began hydrogen desorption at approximately 48 °C, which is very close to ambient temperature. Approximately 6.3 wt % H2 was released from LiAlH4 -10 wt %Ni/C within 60 min at 140 °C, whereas pristine LiAlH4 only released 0.52 wt % H2 under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C under 4 MPa H2 . The synergetic effect of the flower-like carbon substrate and Ni active species contributes to the significantly reduced dehydrogenation temperatures and improved kinetics.

A metal-organic framework based on a longer linear ligand was rationally designed and evaluated as a novel anode material for sodium-ion batteries. It delivered a high specific capacity of 269 mA h g-1 with a desired voltage plateau and demonstrated excellent capacity retention (79.0% after 1000 cycles). In addition, its reaction kinetics was also investigated in detail by performing cyclic voltammetry and a predominantly diffusion-controlled process was clearly revealed.

Efficient hydrogen generation and storage is an essential prerequisite of a future hydrogen economy. Boron hydrides feature high volumetric density and high hydrogen generation, making them a promising candidate for chemical hydrogen storage. The development of efficient non-noble metal catalysts for on-demand hydrogen release through boron-hydride hydrolysis under mild conditions has received extensive interest. Transition-metal boride/phosphide based materials are attractive due to their advantages of earth-abundant elements, considerable catalytic activity, high stability and low cost. In this review, we summarize the recent progress in the synthesis of transition metal boride/phosphide based catalysts and their application in catalyzing hydrolysis of boron hydrides. We highlight a number of strategies to enhance the catalytic efficiency and stability of metal boride/phosphide catalysts, such as component optimizing, structure tailoring and substrate engineering. Remarkably, the supported Co–W–B catalyst enables a high H2 release rate of 15 000 mL min−1 g−1 and an activation energy lower than 30 kJ mol−1 towards the hydrolysis of NaBH4. Furthermore, the main concerns and issues like identifying a real catalytic activity center and revealing the catalytic mechanisms are also discussed, along with perspectives on future research in this field.

We here report on the preparation and Li-ion battery anode application of ultrasmall Sn nanoparticles (∼5 nm) uniformly embedded in spherical hollow carbon. The novel Sn–C composite shows a high Li-storage capacity (743 mA h g−1 at 0.5 A g−1) with unprecedentedly high cyclic stability (92.1% capacity retention after 6000 cycles at 4 A g−1).

Lithium borohydride (LiBH4 ) with a theoretical hydrogen storage capacity of 18.5 wt % has attracted intense interest as a high-density hydrogen storage material. However, high dehydrogenation temperatures and limited kinetics restrict its practical applications. In this study, mesoporous nickel- and cobalt-based oxide nanorods (NiCo2 O4 , Co3 O4 and NiO) were synthesized in a controlled manner by using a hydrothermal method and then mixed with LiBH4 by ball milling. It is found that the dehydrogenation properties of LiBH4 are remarkably enhanced by doping the as-synthesized metal oxide nanorods. When the mass ratio of LiBH4 and oxides is 1:1, the NiCo2 O4 nanorods display the best catalytic performance owing to the mesoporous rod-like structure and synergistic effect of nickel and cobalt active species. The initial hydrogen desorption temperature of the LiBH4 -NiCo2 O4 composite decreases to 80 °C, which is 220 °C lower than that of pure LiBH4 , and 16.1 wt % H2 is released at 500 °C for the LiBH4 -NiCo2 O4 composite. Meanwhile, the composite also exhibits superior dehydrogenation kinetics, which liberates 5.7 wt % H2 within 60 s and a total of 12 wt % H2 after 5 h at 400 °C. In comparison, pure LiBH4 releases only 5.3 wt % H2 under the same conditions.

Rational design of optimal bifunctional oxygen electrocatalyst with low cost and high activity is greatly desired for realization of rechargeable Zn–air batteries. Herein, we fabricate mesoporous thin-walled CuCo2O4@C with abundant nitrogen-doped nanotubes via coaxial electrospinning technique. Benefiting from high catalytic activity of ultrasmall CuCo2O4 particles, double active specific surface area of mesoporous nanotubes, and strong coupling with N-doped carbon matrix, the obtained CuCo2O4@C exhibits outstanding oxygen electrocatalytic activity and stability, in terms of a positive onset potential (0.951 V) for oxygen reduction reaction (ORR) and a low overpotential (327 mV at 10 mA cm–2) for oxygen evolution reaction (OER). Significantly, when used as cathode catalyst for Zn-air batteries, CuCo2O4@C also displays a low charge–discharge voltage gap (0.79 V at 10 mA cm–2) and a long cycling life (up to 160 cycles for 80 h). With desirable architecture and excellent electrocatalytic properties, the CuCo...

Sulfur is a promising alternative lithium battery cathode for its low cost, abundance, and high specific capacity. However, issues of rapid capacity decay and low coulombic efficiency hamper its practical application pace owing to polysulfides dissolution. Despite efforts on hybridizing sulfur with metal oxides to solve these issues are considered to be effective, the synthesis of hybrid materials is always tedious. Herein, S@MnO2 hybrid material was synthesized via a green method at room temperature. We encapsulate S spheres in poly-dopamine (PDA) by in-situ polymerization of dopamine. The formed PDA shell is served as reducing agent and sacrificial template to transform KMnO4 into δ-MnO2 shell without adding any other agents (such as acid). δ-MnO2 encapsulates the S spheres uniformly and succeeded in entrapping polysulfides when S@MnO2 used for Li–S battery, endowing the S@MnO2 cathode with high reversible capacity, improved cycling stability, and satisfied coulombic efficiency. Moreover, this method could be adopted for hybridizing δ-MnO2 with diverse materials (such as CNTs@MnO2) in mild reaction environment (ambient pressure and temperature), exhibiting an extensive application on constructing Mn-based oxide hybrid functional materials.

Metal cobalt has infinite potential for super performance aqueous alkaline batteries. But it is a high degree of requirements to design and synthesize composites to solve the common problems than Co materials. Hence towards that end, Co@N-rich carbon hybrids (CoNC) have been designed and prepared via an in-situ, facile and effective method. By doping abundant nitrogen (about 5 wt%), the mesoporous carbon shells provide more active sites, enhanced electrical conductivity and electrode infiltration, and avoid the Co nanoparticles agglomeration and serious electrode dissolution. When used as the electrode for the aqueous alkaline battery, the CoNC hybrids deliver outstandingly higher discharge capacity, superior high-rate ability, and stable cycling ability. A high discharge capacity of 625 mAh g −1 has been delivered at 500 mA g −1 and reduced to 455.7 mAh g −1 after 150 cycles for the CoNC electrode. Even the current increases up to 5 A g −1 , the capacity still remains at 461.3 mAh g −1 , manifesting the fascinating high-rate discharge ability. Importing the rich nitrogen species makes a significant difference to give full play a positive role on the aqueous alkaline battery, which as well guides a new direction towards high-rate power batteries.

The dehydrogenation behavior of LiBH4 has been investigated when confined into porous NiMnO3 microsphere via a wet chemical impregnation method. The confinement of LiBH4 in the pores of NiMnO3 nanoparticles leads to a significant decrease of the onset and the maximum desorption temperatures. The composites begin to release hydrogen at 150 °C and the maximum desorption temperature is 300 °C, which are much lower compared to the raw LiBH4. Also, the hydrogen release amount is found to be increased. Moreover, the LiBH4@NiMnO3 composites exhibit excellent dehydrogenation kinetics, with 2.8 wt% hydrogen released in 1 h at 300 °C. X-ray diffraction and Fourier transform infrared spectroscopy are used to deduce the desorption mechanism of NiMnO3.

Potassium-ion batteries (KIBs) are considered to be promising energy-storage-systems in the post-Li-ion batteries. Conversion and alloy reaction anode materials draw much attention owing to high theoretical capacities. However, their inherent volume expansions always block the K-ion diffusion or interrupt electron transfer to a degree, resulting in degraded performances at high rates. It is supposed that the rate capability of the anode would be improved when the avenues for ion/electron are kept expedite simultaneously. Herein, SnS2 and carbon hybrid submicro-fibers with optimized channels were prepared as integrated KIBs electrodes to clarify the effect of the bi-continuous avenues on the rate capability. In this configuration, SnS2 nanosheets are confined by carbon and further crosslinked into 3D network. The 3D carbon submicro-fibers are adopted as a network for electron transfer, while the channels play the role of ion diffusion avenues. Owing to the stable and expedite bi-continuous electron/ion avenues, the rate capability of the SnS2@C–1V1 SMF electrode (137.5 mAh g−1 at 2.0 A g−1) is improved when compared to the counterparts (3.6 mAh g−1 and 94.5 mAh g−1 at the same condition). This work will offer an important reference for the optimization design and construction of KIBs anode materials with high rate capability.

Developing highly active electrocatalysts toward oxygen evolution reaction (OER) is critical for the application of water splitting for hydrogen production and can further alleviate the energy crisis problem, but still remaining challenging. Especially, unlocking the catalytic site, in turn, helps design the available catalysts. Herein, the nanorod cobalt telluride with sulfur incorporation grown on a carbon cloth (S-CoTe/CC) as catalysts for OER, which displays extraordinary catalytic activity, is reported. Significantly, the in situ formed CoOOH species on the surface of S-CoTe merited from the structure evolution during the OER process serves as the active species. Furthermore, density functional theory calculations demonstrate that sulfur incorporation can tailor the electronic structure of active species and substantially optimize the free energy, accelerating the OER kinetics. This work provides an in-depth understanding of enhanced OER mechanism through foreign elements incorporating into precatalysts and is beneficial for the guiding design of more efficient catalysts.

To enhance the electronic conductivity of TiO 2 , carbon-coating has been used as a simple and effective method for improving the electrochemical performances of TiO 2 in sodium ion batteries. In this work, considering the internal connection between TiO 2 and the coated carbon-layer, we synthesized carbon-coated TiO 2 composites (TiO 2 /C) via hydrothermal method and subsequent calcination, assisted with different types of surfactant as carbon sources. Due to strong electrostatic attraction, cationic surfactant CTAB (cetyltrimethyl ammonium bromide) generates a uniformly-coated carbon layer onto TiO 2 surface, which enables good electronic conductivity and fast kinetics of the product. Therefore, TiO 2 /C assisted with CTAB as carbon source (TiO 2 /C-C) shows optimal sodium storage performance with excellent specific capacity (303 mA h g −1 at 0.1 C) and satisfying cycling stability, offering promising anode for constructing high capacity sodium ion batteries.

LiBH4@xZZCO composites are successfully synthesized by confining LiBH4 in hierarchical porous ZnO/ZnCo2O4 (ZZCO) nanoparticles via a chemical impregnation method, and the effect of ZZCO on the dehydrogenation performance is systematically investigated. It is found that dehydrogenation properties of LiBH4 are significantly improved, especially for the LiBH4@2ZZCO composite. The onset desorption temperature of LiBH4@2ZZCO is decreased to 169 °C, and the majority of hydrogen release occurs at 275 °C, much lower than raw LiBH4. In addition, 8.7 wt% H2 could be released below 500 °C. Moreover, the apparent activation energy (Ea) has been reduced from 146 kJ/mol (pure LiBH4) to 120.22 kJ/mol. The improved dehydrogenation properties are attributed to the synergistic effect of nanoconfinement and destabilization of ZZCO nanoparticles.

The core-shell Ni 3 N@N-doped carbon (Ni 3 N@NC) was synthesized by a facile sol-gel and heat-treatment process. The as-synthesized core-shell Ni 3 N@NC consisted of an approximately 16 nm Ni 3 N core and a 2 nm N-doped carbon shell. The MgH 2 -xwt%Ni 3 N@NC (x = 3, 5, 10 and 15) composites were prepared by ball-milling method. The hydrogen storage properties of the composites were investigated using isothermal dehydrogenation apparatus and temperature-programmed desorption system. It was found that the MgH 2 -5wt%Ni 3 N@NC composites exhibited the optimal hydrogen storage performance among all the composites. The onset desorption temperature of MgH 2 -5wt%Ni 3 N@NC composites decreased to 175 °C compared to 335 °C for the pure MgH 2 . Moreover, the MgH 2 -5wt%Ni 3 N@NC composites released 6.0 wt% H 2 (only 0.2 wt% H 2 for the pure MgH 2 ) within 20 min at 325 °C. The hydrogen desorption of MgH 2 -5wt%Ni 3 N@NC composites was controlled by a two-dimensional nucleation and growth mechanism.

Transition metal oxides (TMOs) based on conversion reactions are attractive candidate anode materials for lithium-ion batteries (LIBs) because of their high theoretical capacity and safety characteristics. In this review, we have summarized recent progress in the rational design and efficient synthesis of TMOs with controllable morphologies, compositions, and micro-/nanostructures, along with their Li storage behaviors. Single metal oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), chromium (Cr), molybdenum (Mo), and tungsten (W) and their common binary metal oxides have been discussed in this review. Finally, the less well-known merits of conversion reactions are put forward, and the design of metal oxide electrodes making full use of these merits has been proposed.

Graphene monolayers or bilayers highly scattered in porous carbon nanofibers (denoted as G/C) are first prepared by a feasible electrospinning technique. Meanwhile, G/C with the character of a flexible membrane adherent on copper foil is directly used as binder-free anode for Na-ion batteries, exhibiting fascinating electrochemical performance in terms of high reversible capacity (432.3 mA h g−1 at 100 mA g−1), exceptional rate capability (261.1 mA h g−1 even at 10 000 mA g−1), and ultra-long cycling life (91% capacity retention after 1000 cycles). This is due to the synergistic effect between the highly exfoliated graphene layers and the porous carbon nanofibers, which can provide massive active Na-storage sites, ensure sufficient electrolyte infiltration, offer open ionic diffusion channels and oriented electronic transfer pathways, and prevent graphene agglomeration as well as carbon nanofiber fracture upon prolonged cycling. The findings shed new insights into the quest for high-performance carbon-based anode materials of sodium-ion batteries.

Nitrogen-doped hierarchically porous carbon (NHPC) materials have been synthesized by using a zeolitic imidazolate framework, ZIF-8, as self-sacrificing template. The initial derived carbon (D-carbon) contains a 3-dimensional (3D) hierarchically porous carbon framework with rich nitrogen doping (11.22%). Chemical activation by KOH, the further activated carbon (Ac-carbon) shows a specific high surface area (2477 m 2 g −1 ), but lower N content (1.99%). LiBH 4 -(D-carbon)/(Ac-carbon) is prepared by ball-milling method and the dehydrogenation performance of LiBH 4 is significantly improved. More than 6.13 wt% H 2 can be released from either of the two mixtures within 100 min at 320 °C, respectively, showing better dehydrogenation performance than that of pure LiBH 4 . Additionally, the controlled experiments reveal that those improved dehydrogenation properties of LiBH 4 might be attributed to the synergetic contributions of high N heteroatom loading, large surface area and catalysis of carbon materials. We provided a simple method to prepare solely MOF-derived nitrogen-doped carbon materials, which might be a promising catalyst for the hydrogen storage materials.

Zinc-based battery chemistries have lately drawn great attention for grid-scale energy storage due to their material abundance and high safety. However, the low Coulombic efficiency (CE) and dendrite growth of zinc (Zn) anodes and the limited working voltage of current oxide cathodes are the major barriers hindering the development of rechargeable Zn-based batteries (RZBs). Here, we report an ultrafast and high-voltage Zn battery in a new cell configuration employing a graphite cathode, a Zn anode, and nonaqueous 1 M zinc bis(trifluoromethylsulfonyl)imide (Zn(TFSI)

Potassium-ion batteries (KIBs) are promising alternatives to lithium-ion batteries because of the abundance and low cost of K. However, an important challenge faced by KIBs is the search for high-capacity materials that can hold large-diameter K ions. Herein, copper oxide (CuO) nanoplates are synthesized as high-performance anode materials for KIBs. CuO nanoplates with a thickness of ≈20 nm afford a large electrode-electrolyte contact interface and short K+ ion diffusion distance. As a consequence, a reversible capacity of 342.5 mAh g-1 is delivered by the as-prepared CuO nanoplate electrode at 0.2 A g-1 . Even after 100 cycles at a high current density of 1.0 A g-1 , the capacity of the electrode remains over 206 mAh g-1 , which is among the best values for KIB anodes reported in the literature. Moreover, a conversion reaction occurs at the CuO anode. Cu nanoparticles form during the first potassiation process and reoxidize to Cu2 O during the depotassiation process. Thereafter, the conversion reaction proceeds between the as-formed Cu2 O and Cu, yielding a reversible theoretical capacity of 374 mAh g-1 . Considering their low cost, easy preparation, and environmental benignity, CuO nanoplates are promising KIB anode materials.

As indispensable components of potassium ion batteries (KIBs), anode materials are on the focus and their developments are important for boosting the application of KIBs. Tin sulfide (SnS2) is considered as an ideal KIBs anode material owing to its high theoretical capacity (733 mAh g−1) and the unique layered structure. However, the huge volume deformation and potassium polysulfide intermediates dissolution hinder the enhancement of the electrochemical performance of SnS2 anode. Herein, SnS2 nanosheets supported by N, S-doped carbon (N, S-C/SnS2 nanosheets) were synthesized by an in-situ carbonization and sulfuration method with one step. In the formed architecture, the N, S-doped carbon not only works as matrix to stabilize the microstructure of the hybrid material, but also serves as the reservoir to trap polysulfides for alleviating the loss of sulfur element in SnS2. Thanks to these merits, a high reversible capacity (614.8 mAh g−1 at 0.1 A g−1), as well as good rate capability (104.5 mAh g−1 at 2.0 A g−1) are achieved by the N, S-C/SnS2 nanosheets electrode. This work offers a concise method to construct SnS2 hybrid material, and demonstrates that K+ ion storage property of conversion-alloy reaction mechanism sulfide anodes can be remarkably enhanced by elegant structure design.

Ball-milled Ti–B-doped sodium aluminum hydride was directly synthesized via mechanical ball-milling of a NaH/Al mixture. The mixture was completely hydrogenated to NaAlH4 after 70 h under hydrogen pressure of 1 MPa. And higher hydrogen pressure is beneficial for the conversion from NaH/Al mixture to NaAlH4. The dehydrogenation properties of the as-synthesized Ti–B-doped sodium aluminum were systematically investigated. The result shows that ball-milled Ti–B has a remarkable catalytic effect on the enhanced dehydrogenation properties of NaAlH4. As-synthesized Ti–B-doped NaAlH4 sample releases hydrogen at the temperature of about 100 °C. Approximately 4.15 wt% H2 is released from ball-milled Ti–B-doped NaAlH4 at 233.7 °C. Even at 110 °C, it also releases about 2.83 wt% hydrogen. The apparent activation energy (E a) for the first step is estimated to be 83.97 kJ·mol−1 using Arrhenius equation. Thus, utilization of ball-milled Ti–B as catalyst would substantially enhance the practical applications of NaAlH4 for hydrogen storage.

We report on the strategy of Cu doping inducing the nanosize effect of CoO and their application as anode for lithium ion batteries. With an increase of Cu-doped amount, the structures and morphologies of CoO have special changes. The 0.05 mol Cu-doped CoO shows straw-like bundle structure assembled by nanorods, and the nanorods consist of ultra small nanoparticles (about 6–8 nm). Meanwhile, it shows an excellent rates performance and cycle life. The capacity of 800 mA h g−1 is obtained at 0.5 C after 80 cycles. The highest discharge capacity is 580 mA h g−1 at 10 C and the discharge capacities are relatively stable for 1000 cycles as an anode for Li-ion battery. Therefore, the controllable Cu-doped CoO composite could be deemed to be a potential candidate as an anode material.