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Electrochemical water splitting is the most direct and popular method to obtain hydrogen. However, the high activation barrier for water splitting greatly hinders large-scale hydrogen production, inspiring the necessity of using catalysts for the hydrogen evolution reaction and oxygen evolution reaction. Materials from precious metals to earth-abundant transition metals and their composites have been widely developed, in which transition metal selenides display a more outstanding bifunctional catalytic performance. This review aims to focus on the design strategies of transition metal selenide based catalysts from modification methods, including morphological control, anion substitution and cation substitution, as well as using composite materials modified by constructing heterostructures and the synergistic effect of different components. Finally, it provides guidance for the research status, and future development directions of multifunctional electrocatalytic selenide based materials are also suggested.

Zeolitic imidazolate frameworks (ZIF)-derived catalysts are being extensively investigated for the oxygen reduction reaction (ORR) due to its low cost, high tunability, and facile fabrication. However, an understanding of the critical role of temperature during pyrolysis remains lacking, which makes the design of catalysts by thermal activation rely on empirical engineering. In this work, we use ZIF-67 as a model material to study the impact of temperature on microstructural evolution by in situ transmission electron microscopy. Microstructural features of cobalt precipitation, nitrogen loss, and porous carbon support formation were investigated and semi-quantified. A tradeoff between the microstructural features is revealed and confirmed by the ORR performance. By understanding the temperature–microstructure–ORR performance relationship, we further design a simple low-temperature pyrolysis strategy and achieve outstanding ORR activity. Although demonstrated on ZIF-67, the critical role of temperature as disclosed by this work is beneficial for all ZIF-related materials to further boost ORR performance. Meanwhile, our one-step strategy is easy to implement and allows for scaling up for industrial application.

Layered ternary lithium-ion batteries LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) have become mainstream power batteries due to their large specific capacity, low cost, and high energy density. However, these layered ternary lithium-ion batteries still have electrochemical cycling problems such as rapid capacity decline and poor thermal stability. These problems are mainly caused by (1) irreversible phase transition, (2) crack and pulverization of cathode electrode material particles, (3) dissolution of transition metal elements, (4) oxidative decomposition of electrolyte and (5) repeated growth and thickening of the SEI film on the anode electrode. In order to solve these problems, various strategies based on doping and coating of the cathode material, design of electrolyte, and anode coating have been studied to effectively stabilize the NCM/NCA cathode and achieve the purpose of improving its electrochemical cycling performance. This review briefly describes the working principle of lithium-ion batteries, the composition and structure of NCM/NCA cathode materials and the roles of transition metal elements. The capacity degradation mechanism of layered ternary lithium-ion batteries is reviewed from the perspectives of cathode, electrolyte and anode, and the research progress in the modification of cathode materials is emphatically discussed. Advances in the modification of anode materials and electrolyte design are also briefly introduced. Finally, some challenges and prospects are proposed for the future development of layered ternary lithium-ion batteries.

Lithium (Li) metal is a promising anode for high-performance secondary lithium batteries with high energy density due to its highest theoretical specific capacity and lowest electrochemical potential among anode materials. However, the dendritic growth and detrimental reactions with electrolyte during Li plating raise safety concerns and lead to premature failure. Herein, we report that a homogeneous nanocomposite protective layer, prepared by uniformly dispersing AlPO4 nanoparticles into the vinylidene fluoride-co-hexafluoropropylene matrix, can effectively prevent dendrite growth and lead to superior cycling performance due to synergistic influence of homogeneous Li plating and electronic insulation of polymeric layer. The results reveal that the protected Li anode is able to sustain repeated Li plating/stripping for > 750 cycles under a high current density of 3 mA cm−2 and a renders a practical specific capacity of 2 mAh cm−2. Moreover, full-cell Li-ion battery is constructed by using LiFePO4 and protected Li as a cathode and anode, respectively, rendering a stable capacity after 400 charge/discharge cycles. The current work presents a promising approach to stabilize Li metal anodes for next-generation Li secondary batteries.

Metal organic frameworks (MOFs) have been considered as one of the most promising electrode materials for electrochemical capacitors due to their large specific surface area and abundant pore structure. Herein, we report a Co-MOF electrode with a vertical-standing 2D parallelogram-like nanoarray structure on a Ni foam substrate via a one-step solvothermal method. The as-prepared Co-MOF on a Ni foam electrode delivered a high area-specific capacitance of 582.0 mC cm−2 at a current density of 2 mA cm−2 and a good performance rate of 350.0 mC cm−2 at 50 mA cm−2. Moreover, an asymmetric electrochemical capacitor (AEC) device (Co-MOF on Ni foam//AC) was assembled by using the as-prepared Co-MOF on a Ni foam as the cathode and a active carbon-coated Ni foam as the anode to achieve a maximum energy density of 0.082 mW cm−2 at a power density of 0.8 mW cm−2, which still maintained 0.065 mW cm−2 at a high power density of 11.94 mW cm−2. Meanwhile, our assembled device exhibited an excellent cycling stability with a capacitance retention of nearly 100% after 1000 cycles. Therefore, this work provides a simple method to prepare MOF-based material for the application of energy storage and conversion.

Single-atom catalysts provide an effective approach to reduce the amount of precious metals meanwhile maintain their catalytic activity. However, the sluggish activity of the catalysts for alkaline water dissociation has hampered advances in highly efficient hydrogen production. Herein, we develop a single-atom platinum immobilized NiO/Ni heterostructure (PtSA-NiO/Ni) as an alkaline hydrogen evolution catalyst. It is found that Pt single atom coupled with NiO/Ni heterostructure enables the tunable binding abilities of hydroxyl ions (OH*) and hydrogen (H*), which efficiently tailors the water dissociation energy and promotes the H* conversion for accelerating alkaline hydrogen evolution reaction. A further enhancement is achieved by constructing PtSA-NiO/Ni nanosheets on Ag nanowires to form a hierarchical three-dimensional morphology. Consequently, the fabricated PtSA-NiO/Ni catalyst displays high alkaline hydrogen evolution performances with a quite high mass activity of 20.6 A mg−1 for Pt at the overpotential of 100 mV, significantly outperforming the reported catalysts., While H2 evolution from water may represent a renewable energy source, there is a strong need to improve catalytic efficiencies while maximizing materials utilization. Here, authors examine single-atom Pt on nickel-based heterostructures as highly active electrocatalysts for alkaline H2 evolution.

Catalytically active metals atomically dispersed on supports presents the ultimate atom utilization efficiency and cost‐effective pathway for electrocatalyst design. Optimizing the coordination nature of metal atoms represents the advanced strategy for enhancing the catalytic activity and the selectivity of single‐atom catalysts (SACs). Here, we designed a transition‐metal based sulfide‐Ni3S2 with abundant exposed Ni vacancies created by the interaction between chloride ions and the functional groups on the surface of Ni3S2 for the anchoring of atomically dispersed Pt (PtSA‐Ni3S2). The theoretical calculation reveals that unique Pt‐Ni3S2 support interaction increases the d orbital electron occupation at the Fermi level and leads to a shift‐down of the d ‐band center, which energetically enhances H2O adsorption and provides the optimum H binding sites. Introducing Pt into Ni position in Ni3S2 system can efficiently enhance electronic field distribution and construct a metallic‐state feature on the Pt sites by the orbital hybridization between S‐3p and Pt‐5d for improved reaction kinetics. Finally, the fabricated PtSA‐Ni3S2 SAC is supported by Ag nanowires network to construct a seamless conductive three‐dimensional (3D) nanostructure (PtSA‐Ni3S2@Ag NWs), and the developed catalyst shows an extremely great mass activity of 7.6 A mg−1 with 27‐time higher than the commercial Pt/C HER catalyst., A transition‐metal sulfide‐Ni3S2, with abundant exposed Ni vacancies in the outside layers, to anchor and modulate atomically dispersed Pt as the durable catalyst (PtSA‐Ni3S2) for efficiently electrocatalytic hydrogen evolution.

Transition metal selenides (TMSs) have been considering as a kind of promising alternative anode materials for the application of sodium ion batteries due to their high electrical conductivity and high capacity. Here, hollow NiCoSe2 microspheres was prepared via an easy hydrothermal method, followed by the dopamine derived N-doped carbon coated which formed the hollow NiCoSe2@C composite. As-prepared hollow NiCoSe2@C composite has been first used as a new anode material for sodium ion batteries (SIBs). Our selenides displays a quite good electrochemical sodium storage performance. For example, the reversible capacity of as-prepared hollow NiCoSe2@C composite electrode can be maintained at 464.7 mAh g−1 at a current density of 100 mA g−1 after 200 cycles. Moreover, the rate performance of the hollow NiCoSe2@C composite is outstanding. The reversible capacities of 425.3, 420.8, 403.2, 394.7, 378.7, 367.8 and 337.5 mAh g−1 can be achieved at the current densities of 100, 200, 500, 1000, 2000, 3000 and 5000 mA g−1, respectively. Meanwhile, hollow NiCoSe2@C composite electrode exhibits a high discharge capacity of 338 mAh g−1 at a relatively high current density of 0.5 A g−1 after 250 cycles. In addition, the kinetic analysis of electrochemical Na + storage properties of the hollow NiCoSe2@C composite demonstrates that the extrinsic pseudo capacitive behaviour contributes significantly to excellent rate performance and good long-term cycling life. This method can be used to modify the morphologies and structures of the other TMSs for the development of new anode materials as anode materials in the application of sodium ion batteries.

Sodium ion batteries (SIBs) are deemed as the potential alternative for lithium ion batteries (LIBs) in the application of large-scale energy storage and conversion. The favorable anode materials play an important role for high-performance SIBs. Sn4P3 has been considered as one of the promising anode materials for sodium ion batteries due to the combination of high electrical conductivity from Sn and high specific capacity from P. In this work, Sn4P3/graphene aerogel (Sn4P3-GA) composite is prepared via a rapid low-temperature phosphidation reaction from SnO2-GA composite. The structural and morphological characterizations demonstrate that the Sn4P3 nanoparticles with an average size of 8 nm are uniformly and tightly embedded on the surface of 3D GA. The unique 3D network structure as well as the synergistic effect between graphene nanosheets and Sn4P3 nanoparticles would endow the as-prepared Sn4P3-GA composite with good electrochemical sodium storage performance. It delivers the high initial discharge capacity of 1180 mAh g−1 at 0.1 A g−1 and good cycle stability (657 mAh g−1 at 0.1 A g−1 after 100 cycles). Meanwhile, the Sn4P3-GA composite exhibits high-rate capacity of 462 and 403 mAh g−1 at a current density of 1 and 2 A g−1, respectively. Moreover, the contribution of the pseudocapacitance capacity can explicate the origin of good rate capability of the Sn4P3-GA composite. This work demonstrates the great potential of Sn4P3-GA composite as an alternative anode material for the low-cost and high-performance sodium ion batteries.

Rational synthetic design of Sn4P3-based materials with unique morphological structure and superior sodium storage capability for sodium ion batteries (SIBs) is crucially and urgently needed. In th...

SnO2 is considered as one of the most promising alternative anode materials for lithium ion batteries (LIBs) and sodium ion batteries (SIBs) due to high specific capacity, low discharge voltage plateau and environmental friendliness. In this work, 1D ultrafine SnO2 nanorods anchored on 3D graphene aerogel (SnO2 NRs/GA) composite is prepared through a simple reduction-induced self-assembly method in the solution of graphene oxide (GO), Vitamin C and SnO2 nanoparticles. Vitamin C plays an important role in the reduction of GO. The structural and morphological characterizations demonstrate that 1D ultrafine SnO2 nanorods are uniformly and tightly anchored on the surface of 3D graphene nanosheet aerogels. The unique 3D network structure as well as the synergistic effect between 3D graphene nanoshhet and 1D SnO2 nanorods endows the as-prepared SnO2 NRs/GA composite with the good electrochemical lithium/sodium storage performance. It delivers the high initial discharge capacity (1713 mA h g−1 at 0.1 A g−1 for LIBs and 539 mA h g−1 at 0.05 A g−1 for SIBs) and good cycle stability (869 mA h g−1 at 0.1 A g−1 after 50 cycles for LIBs and 232 mA h g−1 at 0.05 A g−1 after 100 cycles for SIBs). Moreover, the SnO2 NRs/GA composite exhibits excellent cycle stability for SIBs with a high reversible capacity of 96 mA h g−1 at as high as 1 A g−1 for 500 cycles. This work provides a simple method to fabricate the electro-active materials-graphene aerogel composites for high-performance LIBs and SIBs.

Flower-like Fe3O4/graphene aerogel (Fe3O4/GA) composite was prepared by water-bath vitamin C reduction self-assembly process followed by a heat treatment under N2 atmosphere. The morphological and structural results demonstrate that 3D flower-like Fe3O4 particles are homogenously embedded into the 3D conductive network of graphene nanosheet aerogels. Based on this unique structure, flower-like Fe3O4/GA composite exhibits a high reversible capacity of 797 mAh g−1 at 0.2 A g−1, and good rate capacity of 551 mAh g−1 at 3.2 A g−1 as well as excellent cycling performance with a stable capacity of ~1138 mAh g−1 after 100 cycles at 0.2 A g−1 compared with bare flower-like Fe3O4 electrode. Our work demonstrates this self-assembly approach can be used to prepare other electroactive metal oxides/graphene composite for the application of lithium ion batteries.

The electro-catalytic performance of the bi-functional catalysts at the air cathode for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) plays a significant role for the development of rechargeable zinc air batteries (ZABs). To obtain the high-performance electrocatalysts, a series of porous Co3O4 samples derived from zeolitic imidazolate framework-67 (ZIF-67) are prepared by one-step annealing process at different temperature (350, 450, and 550 °C) under air atmosphere. Compared with the commercial Co3O4, the optimized sample Co3O4 prepared at 450 °C (CO3O4/C-450) exhibits the lowest overpotential of 1.68 V and the highest half-wave potential of − 0.56 V because the porosity of as-prepared Co3O4 provides abundant reactive sites. Moreover, the high discharge potential of 1.33 V and long cycle life of more than 100 h at 20 mA cm−2 are achieved in ZABs with CO3O4/C-450 electrocatalyst, which are attributed to the better stability provided by the carbon coating.

Designing a simple method to prepare a binder- and carbon-free catalyst with a highly efficient and stable hydrogen evolution electro-catalytic performance in the alkaline media is necessary and urgent. Herein, we develop a low-temperature hydrothermal nitridation and crystal transformation process for the preparation of nitrogen-doped Ni(OH)2 nanobelts decorated on 3D Ni foam (N-Ni(OH)2/NF), where the precursor of amorphous Ni(OH)2/3D Ni foam is fabricated by a simple electrodeposition process. The hydrogen evolution process of our N-Ni(OH)2/NF electrode is studied by using a classical three-electrode electrochemical measurement in the alkaline media. The as-prepared N-Ni(OH)2/NF electrode exhibits a small onset overpotential of 178 mV at 100 mA·cm−2 along with the superior electro-catalytic durability and stability after 10,000 cycles and 24-h continuous operation. The good electrocatalytic hydrogen evolution performance of the N-Ni(OH)2/NF electrode may be attributed to the absence of inactive materials (conducting carbon and binder), the high electrochemical active sites with a double-layer capacitance (Cdl) of 9.33 mF·cm−2, the doping effect of nitrogen atom into Ni(OH)2 crystalline, and the crystal transformation of Ni(OH)2. More importantly, this strategy may be used to modify other transition metal oxides/hydroxides/sulfides/phosphides/selenides for the improved electrocatalytic hydrogen evolution performance.

Transition metal phosphides have attracted increasing attention as anode materials for sodium-ion batteries (SIBs). Cobalt phosphide (CoP) has been deemed as prospective anode materials owing to its high theoretical capacity. Nevertheless, the defects of cobalt phosphides are evident. Low conductivity, the non-negligible volume expansion and aggregation of particles during sodiation/desodiation process result in poor cycling performance and rapid capacity decay, which greatly limit their applications. Herein, we designed a hollow-nanotube structure of sulfur-doped cobalt phosphide (S-CoP) nanoparticles coated by nitrogen-doped porous carbon (S-CoP@NPC), which can be successfully synthesized via an ordinary hydrothermal process followed by the low-temperature phosphorization/sulfuration treatment. The doping of sulfur element provides more active sites, meanwhile, the carbon coating largely helps to avoid the agglomeration of nanoparticles, alleviate volume expansion and improve the conductivity of materials. The S-CoP@NPC composite presents stable cycling performance, showing a discharge specific capacity of 230 mAh g−1 over 370 cycles at 0.2 A g−1. In addition, it also exhibits good rate capability with a discharge specific capacity of 143 mAh g−1 at 5 A g−1, even when the current density returns to 0.2 A g−1, the discharge specific capacity can recover 213 mAh g−1. Furthermore, the kinetic analysis of S-CoP@NPC composite explains that the excellent cycling and rate performance benefit from the extrinsic pseudocapacitive behavior.

It is an efficient and green way to obtain hydrogen with the assistance of highly active and low-cost electrocatalysts by using the electrochemical water electrolysis process in the alkaline electrolyte. Herein, MoO3 particles-decorated Co(OH)2 nanosheet array with a hierarchical nanostructure wrapped Ag nanowires (MoO3-Co(OH)2@Ag NWs) electrocatalysts have been constructed via a two-step electrodeposition method. Ag nanowires have functioned as a conductive network to improve electron transportation ability. As-prepared MoO3-Co(OH)2@Ag NWs catalysts show good HER performance compared with the original Co(OH)2 by delivering at a low overpotential of 220 mV at a current density of −100 mA cm−2, while those for pristine Co(OH)2 and MoO3 are 290 and 412 mV, respectively. The good durability performance of the MoO3-Co(OH)2@Ag NWs catalyst can last for 29 h at a high current density of 100 mA cm−2 with negligible loss, demonstrating the possible commercial application in electrochemical water splitting. A theoretical study has been carried out to understand the reaction kinetics in the generated heterostructure (MoO3-Co(OH)2), which can significantly promote hydrogen evolution reaction process with the reduced adsorption energy of water (Δ G H 2 O *) and decreased Gibbs free-energy of adsorbed H* (ΔGH*) during the hydrogen evolution reaction process. This work can help us to design high-active catalysts with the heterointerface-dependent mechanism for electro-catalytic water splitting processes.

Fe3O4 nanoparticle/graphene aerogel (Fe3O4/GA) composite is fabricated by a simple one-step liquid phase precipitation method without further heat-treatment. The reduction of graphene oxide, deposition of Fe3O4 nanoparticle and formation of 3D graphene nanosheet network can happen simultaneously during preparation process, guaranteeing the uniform distribution of Fe3O4 nanoparticles on the surface of graphene nanosheets. The influence of the graphene amount in the Fe3O4/GA composites on electrochemical performance is investigated. The as-prepared Fe3O4/GA composite with a graphene content of 25% displays good electrochemical lithium storage performance (a high reversible capacity of 985 mAh g−1 at a current density of 0.1 A g−1 after 100 cycles) and good rate capability (434 mAh g−1 at the current density as high as 2 A g−1). Moreover, the contribution of the pseudocapacitance capacity can explicate the origin of good rate capability of the Fe3O4/GA composite. This work demonstrates the great potential of Fe3O4/GA composite as an alternative anode material for the low-cost and high-performance lithium ion batteries.

Sn4P3 is one of the most promising anode materials for sodium ion batteries (SIBs) owning to the alloying reaction of P and Sn with Na to form Na3P and Na15Sn4, which is beneficial to achieve a high specific capacity, especially for the high volumetric capacity (6650 mAh cm−3). However, the high capacities generate large volume changes, which pulverize the anode material, resulting in poor cycling stability. This restricts its practical applications for SIBs. Here, the dopamine-derived N-doped carbon encapsulating hollow Sn4P3 microspheres (hollow Sn4P3@C) composites are prepared by an in-situ self-polymerization of dopamine on the surface of hollow SnO2 microspheres followed by a carbonization process and a low temperature phosphorization using NaH2PO2 as P source. The results of the structural and morphological characterization can be demonstrated that as-prepared hollow Sn4P3@C composites are constructed by hollow Sn4P3 microspheres with the ultrathin N-doped carbon coating. The as-prepared samples are tested as the anode materials for SIBs. Compared with bared hollow Sn4P3 microspheres, hollow Sn4P3@C composites exhibit better electrochemical sodium storage performance. As a result, hollow Sn4P3@C composites deliver the first discharge and charge specific capacities of 840 and 587 mAh g−1 with a high initial coulombic efficiency of 70% at a current density of 0.2 A g−1. Moreover, hollow Sn4P3@C composites display superior rate capabilities of 555, 438, 339, 239, 157 and 92 mAh g−1 at 0.2 A g−1, 0.5 A g−1, 1 A g−1, 2 A g−1, 5 A g−1 and 10 A g−1, respectively. Meanwhile, hollow Sn4P3@C composites show a high discharge capacity of 372 mAh g−1 at 0.2 A g−1 after long 200 cycles. A detailed electrochemical kinetic analysis indicates that energy storage for Na+ in Sn4P3 is due to a pseudocapacitive mechanism. The good electrochemical sodium storage performance of as-prepared hollow Sn4P3@C composites may be attributed to the introduction of N-doped carbon coating and unique hollow structure. Therefore, our work provides a new structure model for the development of new anode materials for SIBs.

Utilized as an oxygen reduction reaction (ORR) catalyst for magnesium-air battery, multi-walled carbon nanotubes (MWCNTs) supported PdSn bimetallic catalyst was synthesized by a facile borohydride reduction method. Heat-treatment was applied to improve the catalytic activity and stability by tailoring the alloying content and surface components of the catalyst. Results illustrated that the 24 h heat-treated PdSn/MWCNTs exhibited best alkaline ORR performance with low over-potential, high diffusion-limited current density and superior stability. A magnesium-air battery employing the 24 h heat-treated PdSn/MWCNTs as cathodic catalyst showed higher discharging power density and enhanced durability compared with those employing the unheated sample and commercial Pd/C catalyst.

CoO has been considered as a novel anode material for lithium storage due to its high theoretical capacity. Herein, mesoporous 3D CoO/nitrogen-doped graphene aerogel (CoO/NGA) is constructed by a facile solvothermal approach followed by subsequent annealing. The NGA is prepared by using dimethylmethanamide (DMF) as a reducing agent and nitrogen source. Ultrafine CoO nanocrystals are homogeneously distributed and tightly anchored on the 3D macroscopic NGA frameworks. The 3D NGA can not only effectively restrain the agglomeration of CoO nanocrystal but also accelerate ion and electron transport through 3D networks. Benefiting from the combine of the two characteristics, the unique CoO/NGA anode exhibits an outstanding cycling stability, showing a specific capacity of 896 mAh g−1 at 200 mA g−1 after 200 cycles.

Efficient catalyst with low overpotential and small Tafel slope for oxygen evolution reaction is the key factor to improve overall efficiency of Zn-air battery. In the present study, a novel hybrid catalyst with polyaniline and amorphous iron-cobalt-binary oxide supporting on multiwalled carbon nanotubes is prepared via a simple in situ method by mixing Fe3+, Co2+, aniline and multiwalled carbon nanotubes together followed by subsequent borohydride reduction with citrate as protective stabilizer. The optimal sample exhibits remarkable activity for oxygen evolution reaction in 0.1 M KOH solution, accompanied by a low overpotential of 440 mV at a current density of 10 mA cm−2, and a small Tafel slope of 55 mV dec−1. Such catalyst can endow rechargeable Zn-air battery with a high peak power density of 287.4 mW cm−2 and long-term cycling performance over 100 h with high efficiency and stability, demonstrating its promising feasibility as highly active electrocatalyst for rechargeable metal-air batteries.

In this study, mesoporous NiCoP microflowers are fabricated by a simple direct low-temperature phosphorization of the hydrothermal-prepared Ni0.5Co0.5(OH)2 microflower precursors. The resultant NiCoP material possesses a unique three-dimensional flower-like architecture with high specifc surface area (56.6 m2 g−1) and large pore volume (0.432 cm3 g−1). Utilized as the supercapacitor electrodes, mesoporous NiCoP microflowers outperform the monometallic phosphides (CoxP and Ni2P microflowers) with excellent charge-discharge rate properties (e.g., specific capacity of 1153 and 715 F g−1 at 1 and 30 A g−1, respectively) and superior cycling performance. The specific capacitance of 883 F g−1 can remain stable at 20 A g−1 after 7000 cycles. More importantly, as-prepared NiCoP microflower electrode is able to deliver high energy densities of 48.4 Wh kg−1 and 30 Wh kg−1 at the power densities of 275 W kg−1 and 8.2 kW kg−1, respectively. The enhanced pseudocapacitive performance is mainly attributed to the mesoporous microflower structure and the synergistic combination of different metal elements (Ni and Co) for electrochemical reactions.

In this paper, MOF-derived N-doped porous carbon anchoring Sn4P3 (Sn4P3@NPC) composite is prepared via a low-temperature phosphidation reaction with SnO2@NPC composite as the precursor. The as-prepared Sn4P3@NPC composite exhibit a high stable capacity of 319 mAh g−1 at 0.1 A g−1 after 100 cycles and improved rate performance (the capacities of 365, 322, 260, 204, and 146 mAh g−1 at 0.1, 0.2, 0.5, 1, and 2 A g−1, respectively) for sodium ion batteries. The good electrochemical sodium storage performance of the Sn4P3@NPC composite anodes can be ascribed to the synergistic effect between porous N-doped carbon and high-active Sn4P3 nanoparticles.

Flower-like MoS2 supported on three-dimensional graphene aerogel (MoS2/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS2 microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS2/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g−1 at a current density of 0.1 A g−1 and good cycling performance (348.6 mAh g−1 after 30 cycles at 0.1 A g−1). The good Na+ storage properties of the MoS2/GA composite could be attributed to the unique structure which flower-like MoS2 are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS2/GA composite has a great potential prospect as anodes for SIBs.

For wide application of metal-air batteries, the key factor is the development of catalysts for air cathodes. In the present study, PdCo/C bimetallic nanocatalysts are prepared by a facile borohydride reduction method. To improve the activity and stability, the catalysts are heat-treated at 200 °C in H2/Ar atmosphere from 4 h to 24 h. The optimal heat-treatment time is found to be 8 h, at which the highest activity for both oxygen reduction reaction and oxygen evolution reaction is obtained. With the 8 h heat-treated PdCo/C catalyst, the rechargeable zinc-air battery exhibits a high power density of 180 mW cm−2 and retains stability for more than 50 h at a discharge-charge current density of 10 mA cm−2, while the magnesium-air battery obtains a power density of more than 200 mW cm−2 and remains stable within 8 h at a discharge current density of 65 mA cm−2.

The development of bifunctional electrochemically-active materials for both hydrogen evolution reaction (HER) and supercapacitors enables the possibility to integrate energy storage and production into one single system. Here, we report a novel bifunctional mesoporous Ni2P nanobelt-like architecture prepared via the hydrothermal synthesis of Ni(SO4)0.3(OH)1.4 nanobelt precursor and subsequent low temperature phosphorization process under Ar atmosphere. Composed of numerous cross-linked Ni2P nanoparticles, the as-obtained Ni2P nanobelts exhibit a two dimensional leaf-like morphology, allowing remarkable enhancement of mesoporosity as well as active surface area. The HER electrocatalytic test in acid medium show a current density of 16 mA cm−2 at an overpotential of 187 mV, Tafel slope of 62 mV dec−1 and long-term durability. Investigation of this Ni2P nanobelts as supercapacitor materials in 2M KOH electrolyte display a high specific capacity ranging from 1074 F g−1 at 0.625 A g−1 to 554 F g−1 at 25 A g−1, and notable cycling life with 86.7% retention after 3000 cycles at 10 A g−1. With the simplicity of the synthetic routine and the outstanding performance as both HER catalysts and supercapacitors, the Ni2P nanobelts provide promising potential for energy devices.

Insufficient lithium resource reserves will severely limit the development prospects of lithium-ion batteries. As the next generation of secondary batteries, sodium-ion batteries have attracted widespread attention. In recent years, people have used synergistic bimetal oxides instead of single metal oxides as anode materials for sodium ion batteries, but its electrochemical performance is still not ideal. Therefore, we synthesized cubic SnO2-Co3O4 hybrids by oxidizing CoSn(OH)6 precursor, and then prepared SnO2-CoO@Gr composites by a simple hydrothermal method. The SnO2-CoO@Gr-2 composite material with the graphene content of 9.6% as an anode material for sodium-ion batteries shows an initial discharge capacity of 598.9 mAh g−1 at a current density of 0.1 A g−1, and still has a reversible capacity of 302.8 mAh g−1 after 200 cycles. The introduction of graphene not only greatly restrains volume expansion of material during the cycle, but also effectively improves the conductivity of the composite material, which provides a great direction for preparing high-performance sodium ion battery anode materials.

In this work, a scalable approach of preparing Co3O4/Co@N–C composite derived from metal organic frameworks (MOFs) is developed. After consecutive carbonization and oxidation of MOFs at different calcination temperatures, a series of nanocomposite consisting of Co3O4, conductive Co nanoparticles, and Nitrogen doped (N-doped) mesoporous carbon are obtained via in-situ polymerization strategy. When employed as anode materials for lithium-ion batteries (LIBs), the Crystalline-Co3O4/Co@N–C-700 (Cry-Co3O4/Co@N–C-700) electrode has shown high reversible specific capacity of 896.5 mAh g−1 at 0.1 A g−1, excellent rate capability of 376.2 mAh g−1 at a large current density of 2 A g−1, and robust long-term capacity retention rate of 96.0% at 0.2 A g−1 after 50 cycles. Such superior lithium storage performance could be attributed to the unique porous structure which composed of well-dispersed Co3O4 and conductive Co nanoparticles together with N-doped carbon skeleton. The unique structure can effectively improve the conductivity and act as a buffer medium to alleviate the volume change, which shows potential application for new energy storage materials.

Traditional metal selenide was used as sodium ion battery anode on account of its high specific capacity and large layer spacing. Here, ZnSe/rGO composites are synthesized through a facile one-step hydrothermal method using relatively environmentally friendly raw materials. The obtained ZnSe nanoparticles with a diameter of about 50 nm, which evenly distributed on the three-dimensional graphene sheet. Electrochemical test results show improved performance, under a current density of 100 mA g−1, the capacity can still remain 276.6 mA h g−1 after 100 cycles. For rate performance, when the current density are under 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g−1, the capacity can remain 411.6, 385.9, 340.1, 293.9, 239.4, 179.2 and 119.4 mA h g−1, respectively. Furthermore, under a large current density of 500 mA g−1, it can remain a reversible capacity of 119.4 mA h g−1. In addition, the calculation of pseudocapacitance shows that it is helpful to achieve pleasing rate capability and long cyclic stability. As a result of its high specific surface area and enhanced electronic conductivity, an improved performance can be obtain, furthermore can well alleviate the volume expansion of the composite.

Transition metal selenide (TMS) is recognized as a prospective alternative anode material for the sodium ion battery application because of its high conductivity and high theoretical capacity. Herein, a simple hydrothermal method was used to prepare the ZIF-8 cubes and then followed by a selenization process to fabricate ZnSe nanoparticles decorated with hollow N-doped carbon (ZnSe/HNC) nanocubes. Our selenides exhibit good electrochemical sodium storage properties. It delivers a high initial discharge and charge capacities of 526.9 and 319.5 mAh g−1 at a current density of 100 mA g−1. The reversible capacity of as-prepared ZnSe/HNC nanocube electrode can be maintained at 335.7 mAh g−1 after 50 cycles at the current density of 100 mA g−1. As for rate capacity, the high reversible capacities of ZnSe/HNC nanocube electrode are 323.6, 306.9, 290.2, 262.0, 202.4, 173.6 and 115.4 mAh g−1 at different current densities of 100, 200, 500, 1000, 2000, 3000, 5000 mA g−1, respectively. In addition, the stability of the ZnSe/HNC nanocube electrode at high current density was also obtained. It can release a high and stable capacity of 251.1 mAh g−1 after 500 cycles at a current density of 500 mA g−1. The electrochemical sodium storage process and the reaction mechanism of the ZnSe/HNC nanocube electrode were confirmed by Ex-situ XRD study. Meanwhile, kinetic analysis of the electrochemical Na+ storage characteristics of the ZnSe/HNC nanocube demonstrates that the behavior of the external pseudocapacitor significantly contributes to good rate performance and good long cycle life. The good sodium storage performance of our ZnSe/HNC nanocube anode material can be attributed to the confinement of charge and discharge products for as-prepared ZnSe/HNC nanocube electrode material and the alleviation of volume change effect for our electrode material during cyclic process. This method can be used to adjust other TMS morphologies and structures to develop a new kind of anode materials for sodium ion battery applications.

Bimetallic selenide (ZnSe / CoSe) was embedded in N-doped carbon rhombic dodecahedron and used as a sodium ion battery (SIB) anode. Metal organic framework (MOF) precursors (ZIF-8 / 67) form hollow structures (denoted as ZnSe/CoSe@NPC)through in situ pyrolysis and selenization processes at specific temperatures. Our selenides have very good electrochemical sodium storage properties. After 200circulation, the capacity of the as-prepared ZnSe/CoSe@NPC nanocomposite electrode was maintained at 417.6 mAh g−1 at 0.1 A g−1. Regarding rate capacity, the capacities of ZnSe/CoSe@NPC nanocomposite electrode are of 460.8, 415.6, 359.9, 346.3, 318.0, 274.1 and 236.4 mAh g−1 at different current densities of 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g−1, respectively. The stability of the ZnSe/CoSe@NPC nanocomposite electrode at high current density is also obtained, and after 900 cycles at a high current density of 1 A g−1, the electrode can maintain a stable reversible capacity of 303.9 mAh g−1. Besides, kinetic analysis of the electrochemical Na+ storage behaviour of the ZnSe/CoSe@NPC nanocomposite shows that the external pseudocapacitor results in excellent rate performance and excellent long-cycle stability. This study proposes a new strategy for synthesizing multi-component hollow structures for the manufacture of intended energy storage devices.

In this work, graphene–polyaniline nanofiber (G/PANI-F) composite is prepared through a new and one-pot method that includes the reduction of graphene oxide (GO) by aniline and then followed by in-situ polymerization. Aniline plays the two roles in this method: as a chemical reducing agent to reduce GO to graphene and as a monomer to prepare polyaniline nanofiber (PANI-F). Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy and transmission electron microscopy are employed to confirm that GO can be reduced by aniline and PANI-F can be deposited on the surface of graphene. The electrochemical properties of G/PANI-F composite electrode are measured by using cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. The G/PANI-F composite electrode exhibits enhanced specific capacitance of 965 F g−1 at 0.5 A g−1 and the capacity retention is 90% after 2000 cycles.

Polyaniline nanofiber-graphene oxide (PANIF-GO) hybrids were fabricated by oil–water interfacial polymerization. The structures of PANIF-GO hybrids, pure PANIF and GO were examined by high resolution transmission electron microscopy. It was found that PANIFs were homogeneously inserted between the GO layers or absorbed on the surface of the GO. Fourier transform infrared spectroscopy and X-ray diffraction showed that PANIFs effectively increased the interlayer distance of GO from 0.83 nm to 1.38 nm. Electrochemical properties for the hybrid electrode were tested by cyclic voltammetry and electrochemical impedance spectroscopy using a three-electrode system. The results indicated that a high specific capacitance of 564.7 F g−1 for the hybrids was measured at the current density of 0.5 A g−1 in a 1 M H2SO4 aqueous solution compared to 352.8 F g−1 for pure PANIF and 30.1 F g−1 for GO. Moreover, the PANIF-GO hybrids showed a very long cycle life with only 9.4% specific capacitance loss after 2000 cycles. The as-prepared hybrids are remarkable electrode materials for the supercapacitors.

Reduced graphene oxide/CoFe 2 O 4 –Co (RGO/CFC) nanocomposite was first prepared by a facile hydrothermal strategy and subsequently in situ reduction process. X-ray diffraction, Raman spectra, and scanning electron microscopy are employed to characterize the structure and morphology of the as-prepared RGO/CFC nanocomposite. The electrochemical performances of the nanocomposite were evaluated in coin-type cells. It delivers high reversible capacity of 921.8 mA h g −1 at various rates from 100 to 1600 mA g −1 after 70 cycles. Even after 420 cycles at 9000 mA g −1 , the capacity still retains 907.3 mA h g −1 at 100 mA g −1 , indicating outstanding rate capability and cycle stability. The improved electrochemical performance is ascribed to the strong interfacial interaction between CFC nanoparticles (30 nm) and RGO nanosheets. The RGO/CFC nanocomposite with super long cycling life will be an ideal candidate of anode material for lithium ion batteries.

The CoFe 2 O 4 –Co rods with diameters in the range of 300–700 nm and length extending from 1 to 4 μm were synthesized successfully by a facile in situ method. A transmission electron microscopy image has shown that the as-formed CoFe 2 O 4 –Co rods are composed of smaller nanocrystallines. The CoFe 2 O 4 –Co rods as anode materials for lithium ion batteries indicate high reversible capacity of 574.3 mAh g −1 at 100 mA g −1 in the first cycle, and good rate capability at various current densities between 100 and 1600 mA g −1 . The improved electrochemical performance is ascribed to the presence of the metallic Cobalt and the well-designed rod structure.

An easy and one-pot method for the preparation of sulfonated graphene–polyaniline nanofiber (SGEPA) composites by oil/water interfacial polymerization was studied in this work. Among the composites were obtained at different mass ratios of graphene and aniline. The chemical structure of the materials was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The morphology of the material was studied by scanning electron microscope and high resolution transmission electron microscopy. The SGEPA composite electrodes with a mass ratio of 1:10 showed better electrochemical performance than pure polyaniline nanofiber and graphene. A high specific capacitance of 962 F/g was obtained at a potential scan rate of 2 mV/s and the specific capacitance value of SGEPA-110 retained about 78% after 1000 cycles. It also exhibited a high energy density of 68.86 Wh/kg at a power density of 102 W/kg. The extraordinary electrochemical properties of the composites were attributed to the well-designed structural advantages of binary nanocomposites and the good combination and synergistic effects between graphene and polyaniline.

We developed one-spot in situ synthesis method to fabricate CoO/reduced graphene oxide (CoO/RGO) nanocomposite by directly employing C4H6O4·Co·4H2O and hydrophilic graphite oxides as raw materials. The electrochemical performances of the as-prepared CoO/RGO nanocomposite were evaluated in coin-type cells. It delivers a high reversible capacity of 740.7 mAh g−1 at 100 mA g−1, and retains a capacity retention of 95% after 50 cycles. Even after 435 cycles at various rates from 100 to 4000 mA g−1, the capacity still retains 577.9 mAh g−1 when the current density is back to 100 mA g−1. The extraordinary performance is ascribed to the well-designed structure of the CoO/RGO nanocomposite. The small-sized, high crystalline and dense CoO nanoparticles uniformly disperse on conductive graphene substrates, supplying large number of accessible active sites for lithium-ion insertion, short diffusion length for lithium ions, good conductivity and strong interfacial interaction between CoO nanoparticles and RGO nanosheets, which are beneficial for high capacity and long cycling stability.

Dispersive calcium carbonate (CaCO 3 ) particles were synthesized at 40 °C via the modified carbonation route developed in this paper. The influence of MgCl 2 on the dispersion behavior of the slaking slurry and the carbonation product were investigated using a laser particle size analyzer and a zeta potential analyzer, the corresponding changes of the morphology and the structure were identified by the field scanning electron microscopy (FSEM) and X-ray diffractometry (XRD), respectively. The experimental results indicated that the addition of MgCl 2 in the Ca(OH) 2 slurry converted the Ca(OH) 2 agglomerates to the dispersive Mg(OH) 2 particles, the carbonation of the slaking slurry containing Mg(OH) 2 and CaCl 2 led to the formation of the dispersive CaCO 3 (calcite) cubic particles with a particle size of 0.3–0.8 μm and a mean agglomerate size of 1.3 μm.