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Capping agents are frequently used in the chemical synthesis of materials, to precisely tailor the size, shape, and composition, with the expectation of high-performance catalysis. However, the adsorbed capping agents also serve as a physical barrier to restrict the interaction between reactants and catalytically active sites on the material surface. In this article, an in situ tailored interface strategy is introduced for effectively removing capping agents (long-chain oleylamine) from the surface of copper sulfide, to maximize the catalytic activity. The interface long-chain molecules of oleylamine are replaced by the inorganic S2− ion via a facile stirring approach without harsh processing conditions or the need for additional non-commercial materials. The as-cleaned copper sulfide shows greatly enhanced activity toward lithium–sulfur batteries, with an impressive current rate, excellent cycling stability, and great rate capability. These "clean surface" strategies using interface engineering provide a significant insight into the structure–activity relationships to support advancements in electrocatalysis technology in lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

The electrochemical nitrogen reduction reaction (NRR) over single‐atom catalysts (SACs) anchored on Mo vacancies of Mo2CO2 MXene nanosheets under ambient conditions suffers from poor selectivity, low yield, and low Faradaic efficiency because of their sluggish kinetics and the competing hydrogen evolution reaction. Herein, density functional theory calculations are performed to improve the understanding of the selectivity and yielding of ammonia through NRR over various isolated SACs, that is, from Sc to Au, anchored on the Mo vacancy of the Mo2CO2 MXene nanosheet (denoted as MO2CO2‐MSA). The potential‐determining step of the NRR shows that eight candidates (i.e., Y, Zr, Nb, Hf, Ta, W, Re, and Os) confined on the defective Mo2CO2 layer could promote the electroreduction from N2 to NH3. Among these, Mo2CO2‐YSA presented the lowest reported reaction Presents the lowest reported reaction energy barrier (0.08 eV) through the distal pathway and high selectivity to NRR compared with the previously synthesized Mo2CO2‐RuSA with a relatively high energy barrier (0.65 eV) and poor selectivity. In addition, the formation energy of Mo2CO2‐YSA is more negative than that of the Mo2CO2‐RuSA catalyst, suggesting that the experimental preparation of the Mo2CO2‐YSA catalyst is highly feasible. This work lays a solid foundation for improving the rational design of MXene‐based systems as efficient electrocatalysts for the synthesis of ammonia. [ABSTRACT FROM AUTHOR]

Fabrication of binder‐free electrodes is an effective way to increase the performance of electrochemical energy storage (EES) devices, such as rechargeable batteries and supercapacitors. In traditional electrodes, the binder is usually electrochemically inert and has weak interactions and interfaces between binder and the active material, which increase "dead mass" and directly affect the performance of energy storage system. The binder‐free electrode can provide well‐designed electrode material structure enables well connection between active materials themselves and current collectors. In addition, without insulating binder, electron and electrolyte ions can transfer more efficiently within the electrode materials. Here, we reviewed research efforts in using various techniques involving chemical, physical and electrical methods to fabricate binder‐free electrodes. For every technique, we first briefly describe their principle and involved factors that influence the performance of as‐fabricated binder‐free electrodes and summarize advantages and disadvantages. Next, we reviewed several works which have used this technique to fabricate binder‐free electrodes. Further, the effect of well‐crafted structure design on the properties of energy storage performances including rate capability, and cycle stability was highlighted. Last, we offer our perspectives on the challenges and potential future research directions in this area. We hope this review can stimulate more research to design and synthesize the binder‐free materials for EES devices. [ABSTRACT FROM AUTHOR]

The well‐matched technology of cathode and anode in Na‐ion full batteries is highly challenging yet critically important in practical applications. Here, the high‐performance Na‐ion full batteries are developed by using NaTi2(PO4)3/N‐doped mesoporous hard carbon hybrid anode and porous Na3V2(PO4)3 cathode. The different anodes are designed for well‐matched Na‐ion full batteries. The unique sandwich and mesoporous structural features endow the hybrid anode with a high reversible capacity (240 mAh g−1 at 1 C), high rate performance (109.7 mAh g−1 at 100 C), ultrahigh energy/power densities (76.56 Wh kg−1/5104 W kg−1) and a long cycle‐life (capacity retention of 92.1 % after 1000 cycles at 100 C) in a half cell. In a full battery this hybrid anode can also deliver a higher capacitive contribution (79.5–87.7 %) and high energy/power densities (104 Wh kg−1/5256 W kg−1). This design provides a promising pathway for developing high performance and low‐cost Na‐ion full batteries. [ABSTRACT FROM AUTHOR]

Cobaltite systems with spinel structures are promising cathode materials for next-generation high-performance electrochemical capacitors because of their high electrochemical stability. However, increasing the mass loading of active materials without sacrificing the geometry of the nanostructures remains a challenge. In this study, we propose vertically stacked bilayer spinel heterostructures constructed from hierarchical CuCo2O4/MnCo2O4 on graphite paper as highly capable supercapacitor electrodes. A two-step hydrothermal method with post annealing treatment is used in the preparation of the heterostructures. The CuCo2O4/MnCo2O4 electrode delivers a remarkable specific capacitance of 1434 F g−1 at 0.5 A g−1, considerable high-rate capability (810 F g−1 at 15 A g−1), and an excellent cycling stability, maintaining 81.4% at 10 A g−1 after 5000 cycles. An electrochemical capacitor device operating at 1.6 V is also constructed using CuCo2O4/MnCo2O4 and graphene as positive and negative electrodes, respectively. The device shows a high energy density of 42.1 W h kg−1 at a power density of 400 W kg−1, as well as good cycling stability (88.4% retention after 10 000 cycles). The concept of stacking heteronanostructures can potentially enrich the electrochemical performance of metal oxides for next-generation electrochemical capacitors. [ABSTRACT FROM AUTHOR]

We have developed a high performance supercapacitor cathode electrode composed of well dispersed MnCO3 quantum dots (QDs, ∼1.2 nm) decorated on nickel hydrogen carbonate–manganese carbonate (Ni(HCO3)2–MnCO3) hedgehog-like shell@needle (MnCO3 QDs/NiH–Mn–CO3) composites directly grown onto a 3D macro-porous nickel foam as a binder-free supercapacitor electrode by a facile and scalable hydrothermal method. The MnCO3 QDs/NiH–Mn–CO3 composite electrode exhibited a remarkable maximum specific capacitance of 2641.3 F g−1 at 3 A g−1 and 1493.3 F g−1 at 15 A g−1. Moreover, the asymmetric supercapacitor with MnCO3 QDs/NiH–Mn–CO3 composites as the positive electrode and graphene as the negative electrode showed an energy density of 58.1 W h kg−1 at a power density of 900 W kg−1 as well as excellent cycling stability with 91.3% retention after 10 000 cycles, which exceeded the energy densities of most previously reported nickel or manganese oxide/hydroxide-based asymmetric supercapacitors. The ultrahigh capacitive performance is attributed to the presence of the high surface area core–shell nanostructure, the well dispersed MnCO3 quantum dots, and the high conductivity of MnCO3 quantum dots as well as the synergetic effect between multiple transition metal ions. The superior supercapacitive performance of the MnCO3 QDs/NiH–Mn–CO3 composites makes them promising cathode materials for high energy density asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

A 3D hybrid nickel-aluminum layered double hydroxide (NiAl-LDH)–graphene nanosheets (GNS) composite as a supercapacitor material has been fabricated by in situ deposition of LDH nanosheets on graphene oxide (GO) through a liquid phase deposition method. The results reveal that NiAl-LDH homogeneously grew on the surface of GNS as spacers to keep the neighboring sheets separate. Optimum effects could be achieved when feeding ratio, reaction time and temperature are tuned. The obtained porous GNS/NiAl-LDH composite exhibited high-capacitance performance with a specific capacitance of 1255.8 F g−1 at a current density of 1 A g−1 and 755.6 F g−1 at 6 A g−1, respectively. Moreover, the composite exhibited excellent cycling performance with an increase of 6% capacitance compared with the initial capacitance after 1500 cycle tests. Such high specific capacitance, rate capability and exceptional cycling ability of the composite offered great promise in energy storage device applications. [ABSTRACT FROM AUTHOR]

Defects in nanocarbon materials can trigger their intriguing electrochemical properties and potential applications, but their synthesis is challenging. Herein, we report the synthesis of ultrathin nitrogen-doped carbon nanosheets with intrinsic defects through the pyrolysis of ZIF-8 with linker vacancies. The as-synthesized electrocatalyst exhibits excellent oxygen reduction reaction (ORR) activity with an onset potential and half-wave potential of 1.05 and 0.873 V vs. RHE, respectively, outperforming the reported metal-free ORR electrocatalysts. It also shows a commercial Pt/C-comparable performance in zinc–air battery with a power density of 154.4 mW cm−2. Characterization and DFT calculation results suggest the adjacent sp3-carbon in carbon pentagon can significantly strengthen the adsorption and activation of oxygen molecules on sp2-carbon, hence the potential determining step is altered and ORR overpotential is lowered. This work highlights a promising green synthesis strategy of MOF-derived metal-free nanocarbon materials for wide application in advanced energy technologies. [Display omitted] • Hydrothemal synthesis of ZIF-8 with linker vacancies by addition of boric acid. • Rich edge sites, carbon pentagon and sp3 hybrization in derived metal-free carbon. • Superior ORR and zinc–air battery performance among reported metal-free materials. • Synergistic effect of topological defect and hybrization state. [ABSTRACT FROM AUTHOR]

• TiO 2 nanosheets and RGO layers modify MoS 2 layers to realize porous hierarchical. • The porous hierarchical architecture improves electrons and ions transport for SIBs. • The synergistic effect among TiO 2 , MoS 2 and RGO improves electrochemical performance. To enhance the reversible capacity and cycle stability of MoS 2 as anode materials for sodium ion batteries (SIBs), we constructed a hybrid architecture composed of MoS 2 and TiO 2 nanosheets, linking with reduced graphene oxide (RGO) to another TiO 2 /MoS 2 to form a nanoflower structure. Owing to layered RGO coupled with TiO 2 /MoS 2 hybrid, such a composite offered interconnected conductive channels to short shuttle path of Na+ ions and favorable transport kinetics under charge/discharge cycling. Moreover, this unique structure showed a porous and hierarchical architecture, which not only buffered volume changes but also provided more electrochemical active sites during insertion/deintercalation processes of Na ions. Outstanding electrochemical performances were identified by the component matching effect among TiO 2 , MoS 2 and RGO with a three-dimensional (3D) interconnected network, exhibiting a good reversible capacity of 616 mA h g−1 after 100 cycles at 0.1 A g−1, an excellent rate capability of 250 mA h g−1 even at 5A g−1 and a long cycling stability of 460 mA h g−1 with a capacity fluctuation of 0.03% per cycle within 350 cycles at 1 A g−1. [ABSTRACT FROM AUTHOR]

NaSn2(PO4)3 has open framework, high ionic conductivity, low working potential, high theoretical capacity more than twice of graphite. However, its commercial application is limited by its low electrical conductivity and rapid capacity fading. To overcome this challenge, we synthesize NaSn 2 (PO 4) 3 submicro-particles (around 100–300 nm in size) by hydrothermally assisted pyrolysis reactions. The synthesized NaSn 2 (PO 4) 3 anode for Na/Li mixed-ion batteries delivers an ultrahigh initial discharge capacities, excellent rate performance and superior cycling stability. This design provides a promising pathway for developing high performance mixed-ion batteries. Image 1 • NaSn 2 (PO 4) 3 submicro-particles are synthesized by hydrothermally assisted pyrolysis reactions. • The submicro-particle anode exhibits an ultrahigh discharge capacity of 1868.5 mAh g−1 at 0.1 A g−1. • This anode has excellent cycling stability (capacity retention of 106% after 200 cycles at 5 A g−1). • The synthesis mechanism of NaSn 2 (PO 4) 3 submicro-particles is evaluated. [ABSTRACT FROM AUTHOR]

Na 2 FeSiO 4 (NFS)/H–N-doped hard carbon nanospheres (HN-HCNSs) hybrid cathodes have been synthesized by using ferrous gluconate as template and carbon source via sol-gel method for the first time. In the structure of this hybrid cathode, the ultrathin NFS nanosheets are uniformly anchored in the mesoporous network structure of HN-HCNSs coating, forming the fast conductive transport pathways for electrons and Na+-ions. The NFS/HN-HCNSs hybrid cathode shows a hybrid energy storage mechanism with high initial discharge capacity of 218.4 mAh g−1 at 0.1 C and in the voltage range of 1.2–4.6 V versus Na/Na+. It also shows excellent long-term cycling stability (the capacity retention rates of 73.8% at 1 C after the 3300 cycles and 56.8% at 5 C after the 750 cycles in the voltage range of 1.5–4.6 V). Moreover, the unique mesoporous carbon-coated structural features endow the hybrid cathode with a maximum energy density of 331.99 W h kg−1 and a maximum power density of 2431.87 W kg−1 within working voltage range of 1.5–4.6 V. Image 1 • Na 2 FeSiO 4 /H–N-doped mesoporous hard carbon nanosphere hybrid cathodes was synthesized. • Ferrous gluconate template controlled the formation of mesoporous carbon-coated structure. • This structure gives a remarkable synergic effect of Na-ion battery-supercapacitor. • This hybrid electrode delivers high energy and power densities. [ABSTRACT FROM AUTHOR]