A novel and simple nitrogen-doped carbon/polyaniline electrode material for supercapacitors

We demonstrated a simple and environment-friendly method in thepreparation of N-doped carbon/PANI(NCP)composite without binder.The structureand the property of NCP have been characterized by XPS,IR,XRD,SEM,CV,GCD and EIS.The results reveal that NCP has high capacitance performance of up to 615 F·g^-1at 0.6A·g^-1.Additionally,the asymmetric NCP₃₀₀/lcarbon supercapacitor delivers a highcapacitance(111 F·g^-1at 1A·g^-1)and a capacity retention rate of 82%after 1200 cyclesat 2A·g^-1.The ASC cell could deliver a high energy density of 39.1 W·h·kg^-1at a powerdensity of 792.6 W·kg^-1.     

Two-step preparation of carbon nanotubes/RuO2/polyindole ternary nanocomposites and their application as high-performance supercapacitors

A ternary single-walled carbon nanotubes/RuO₂/polyindole (SWCNT/RuO₂/PIn) nanocomposite was fabricated by the oxidation polymerization of indole on the prefabricated SWCNT/RuO₂ binary nanocomposites. The nanocomposite was measured by FTIR, XRD, SEM, TEM, EDS and XPS, together with the electrochemical technique. The electrochemical results demonstrated that the symmetric supercapacitor used SWCNT/RuO₂/PIn as electrodes presented 95% retention rate after 10000 cycles, superior capacitive performance of 1203 F·g⁻¹ at 1 A·g⁻¹, and high energy density of 33 W·h·kg⁻¹ at 5000 W·kg⁻¹. The high capacitance performance of SWCNT/RuO₂/PIn nanocomposite was mainly ascribed to the beneficial cooperation effect among components. This indicated that the SWCNT/RuO₂/PIn nanocomposite would be a good candidate for high-performance supercapacitors.     

Feather-like NiCo2O4 self-assemble from porous nanowires as binder-free electrodes for low charge transfer resistance

The unique feather-like arrays composing of ultrathin secondary nanowires are fabricated on nickel foam (NF) through a facile hydrothermal strategy. Thus, the enhancement of electrochemical properties especially the low charge transfer resistance strongly depends on more active sites and porosity of the morphology. Benefiting from the unique structure, the optimized NiCo₂O₄ electrode delivers a significantly lower charge transfer resistance of 0.32 Ω and a high specific capacitance of 450 F·g⁻¹ at 0.5 A·g⁻¹, as well as a superior cycling stability of 139.6% capacitance retention. The improvement of the electrochemical energy storage property proves the potential of the fabrication of various binary metal oxide electrodes for applications in the electrochemical energy field.     

Chestnut shell-like N-doped carbon coated NiCoP hollow microspheres for hybrid supercapacitors with excellent electrochemical performance

In this work, transition metal phosphides (TMPs) were reinforced by a solvothermal synthesis method and in situ polymerization in dopamine with one-step phosphating and carbonizing process to form chestnut shell-like N-doped carbon coated NiCoP (NiCoP@N-C) hollow microspheres. Excellent morphologic structure is still reflected in NiCoP@N-C, which is suitable for rapid electron and electrolyte transfer. Benefiting from the excellent structure, the coating of N-doped carbon, and the synergistic effect of Ni and Co, NiCoP@N-C reveals excellent electrochemical properties (high specific capacitance of 1660 F·g⁻¹ (830 C·g⁻¹) at 1 A·g⁻¹). In addition, a NiCoP@N-C//carbonization HKUST-1 (HC) achieves high specific energy of 51.8 Wh·kg⁻¹, ultrahigh specific power of 21.63 kW·kg⁻¹, and excellent cycling stability up to 10000 cycles (a capacitance retention of 96.7%). The results show that the NiCoP@N-C electrode material has a wide application in supercapacitors and other energy storage devices.     

FeS2@C nanorods embedded in three-dimensional graphene as high-performance anode for sodium-ion batteries

FeS₂ has drawn tremendous attention as electrode material for sodium-ion batteries (SIBs) due to its high theoretical capacity and abundant resources. However, it suffers from severe volume expansion and dull reaction kinetics during the cycling process, leading to poor rate capacity and short cyclability. Herein, a well-designed FeS₂@C/G composite constructed by FeS₂ nanoparticles embedded in porous carbon nanorods (FeS₂@C) and covered by three-dimensional (3D) graphene is reported. FeS₂ nanoparticles can shorten the Na⁺ diffusion distance during the sodiation–desodiation process. Porous carbon nanorods and 3D graphene not only improve conductivity but also provide double protection to alleviate the volume variation of FeS₂ during cycling. Consequently, FeS₂@C/G exhibits excellent cyclability (83.3% capacity retention after 300 cycles at 0.5 A·g⁻¹ with a capacity of 615.1 mA·h·g⁻¹) and high rate capacity (475.1 mA·h·g⁻¹ at 5 A·g⁻¹ after 2000 cycles). The pseudocapacitive process is evaluated and confirmed to significantly contribute to the high rate capacity of FeS₂@C/G.     

Stabilizing Co3O4 nanorods/N-doped graphene as advanced anode for lithium-ion batteries

Tricobalt tetroxide (Co₃O₄) is one of the promising anodes for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, the poor electrical conductivity and the rapid capacity decay hamper its practical application. In this work, we design and fabricate a hierarchical Co₃O₄ nanorods/N-doped graphene (Co₃O₄/NG) material by a facile hydrothermal method. The nitrogen-doped graphene layers could buffer the volume change of Co₃O₄ nanorods during the delithium/lithium process, increase the electrical conductivity, and profit the diffusion of ions. As an anode, the Co₃O₄/NG material reveals high specific capacities of 1873.8 mA·h·g⁻¹ after 120 cycles at 0.1 A·g⁻¹ as well as 1299.5 mA·h·g⁻¹ after 400 cycles at 0.5 A·g⁻¹. Such superior electrochemical performances indicate that this work may provide an effective method for the design and synthesis of other metal oxide/N-doped graphene electrode materials.     

Crystalline and amorphous MnO2 cathodes with open framework enable high-performance aqueous zinc-ion batteries

Currently, δ-MnO₂ is one of the popularly studied cathode materials for aqueous zinc-ion batteries (ZIBs) but impeded by the sluggish kinetics of Zn²⁺ and the Mn cathode dissolution. Here, we report our discovery in the study of crystalline/amorphous MnO₂ (disordered MnO₂), prepared by a simple redox reaction in the order/disorder engineering. This disordered MnO₂ cathode material, having open framework with more active sites and more stable structure, shows improved electrochemical performance in 2 mol·L⁻¹ ZnSO₄/0.1 mol·L⁻¹ MnSO₄ aqueous electrolyte. It delivers an ultrahigh discharge specific capacity of 636 mA·h·g⁻¹ at 0.1 A·g⁻¹ and remains a large discharge capacity of 216 mA·h·g⁻¹ even at a high current density of 1 A·g⁻¹ after 400 cycles. Hence disordered MnO₂ could be a promising cathode material for aqueous ZIBs. The storage mechanism of the disordered MnO₂ electrode is also systematically investigated by structural and morphological examinations of ex situ, ultimately proving that the mechanism is the same as that of the δ-MnO₂ electrode. This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.     

Conductive polypyrrole incorporated nanocellulose/MoS2 film for preparing flexible supercapacitor electrodes

Conductive films have emerged as appealing electrode materials in flexible supercapacitors owing to their conductivity and mechanical flexibility. However, the unsatisfactory electrode structure induced poor output performance and undesirable cycling stability limited their application. Herein, a well-designed film was manufactured by the vacuum filtration and in-situ polymerization method from cellulose nanofibrils (CNFs), molybdenum disulfide (MoS₂), and polypyrrole. The electrode presented an outstanding mechanical strength (21.3 MPa) and electrical conductivity (9.70 S·cm⁻¹). Meanwhile, the introduce of hydrophilic CNFs induced a desirable increase in diffusion path of electrons and ions, along with the synergistic effect among the three components, further endowed the electrode with excellent specific capacitance (0.734 F·cm⁻²) and good cycling stability (84.50% after 2000 charge/discharge cycles). More importantly, the flexible all-solid-state symmetric supercapacitor delivered a high specific capacitance (1.39 F·cm⁻² at 1 mA·cm⁻²) and a volumetric energy density (6.36 mW·h·cm⁻³ at the power density of 16.35 mW·cm⁻³). This work provided a method for preparing composite films with desired mechanical and electrochemical performance, which can broaden the high-value applications of nanocellulose.     

SrTiO3/TiO2 heterostructure nanowires with enhanced electron--hole separation for efficient photocatalytic activity

Heterostructure is an effective strategy to facilitate the charge carrier separation and promote the photocatalytic performance. In this paper, uniform SrTiO₃ nanocubes were in-situ grown on TiO₂ nanowires to construct heterojunctions. The composites were prepared by a facile alkaline hydrothermal method and an in-situ deposition method. The obtained SrTiO₃/TiO₂ exhibits much better photocatalytic activity than those of pure TiO₂ nanowires and commercial TiO₂ (P25) evaluated by photocatalytic water splitting and decomposition of Rhodamine B (RB). The hydrogen generation rate of SrTiO₃/TiO₂ nanowires could reach 111.26 mmol·g⁻¹·h⁻¹ at room temperature, much better than those of pure TiO₂ nanowires (44.18 mmol·g⁻¹·h⁻¹) and P25 (35.77 mmol·g⁻¹·h⁻¹). The RB decomposition rate of SrTiO₃/TiO₂ is 7.2 times of P25 and 2.4 times of pure TiO₂ nanowires. The photocatalytic activity increases initially and then decreases with the rising content of SrTiO₃, suggesting an optimum SrTiO₃/TiO₂ ratio that can further enhance the catalytic activity. The improved photocatalytic activity of SrTiO₃/TiO₂ is principally attributed to the enhanced charge separation deriving from the SrTiO₃/TiO₂ heterojunction.     

Honeycomb-like polyaniline for flexible and folding all-solid-state supercapacitors

Porous polyaniline (PANI) was prepared through an efficient and costeffective method by polymerization of aniline in the NaCl solution at room temperature. The resulting PANI provided large surface area due to its highly porous structure and the intercrossed nanorod, resulting in good electrochemical performance. The porous PANI electrodes showed a high specific capacitance of 480 F·g^-1, 3 times greater than that of PANI without using the NaCl solution. We also make chemically crosslinked hydrogel film for hydrogel polymer electrolyte as well as the flexible supercapacitors (SCs) with PANI. The specific capacitance of the device was 234 F·g^-1 at the current density of 1 A·g^-1. The energy density of the device could reach as high as 75 W·h·kg^-1 while the power density was 0.5 kW·kg^-1, indicating that PANI be a promising material in flexible SCs.     

Electrochemical performances of NiO/Ni2N nanocomposite thin film as anode material for lithium ion batteries

Despite the high specific capacities, the practical application of transition metal oxides as the lithium ion battery (LIB) anode is hindered by their low cycling stability, severe polarization, low initial coulombic efficiency, etc. Here, we report the synthesis of the NiO/Ni₂N nanocomposite thin film by reactive magnetron sputtering with a Ni metal target in an atmosphere of 1 vol.% O₂ and 99 vol.% N₂. The existence of homogeneously dispersed nano Ni₂N phase not only improves charge transfer kinetics, but also contributes to the one-off formation of a stable solid electrolyte interphase (SEI). In comparison with the NiO electrode, the NiO/Ni₂N electrode exhibits significantly enhanced cycling stability with retention rate of 98.8% (85.6% for the NiO electrode) after 50 cycles, initial coulombic efficiency of 76.6% (65.0% for the NiO electrode) and rate capability with 515.3 mA·h·g⁻¹ (340.1 mA·h·g⁻¹ for the NiO electrode) at 1.6 A·g⁻¹.     

One-step gas-phase construction of carbon-coated Fe3O4 nanoparticle/carbon nanotube composite with enhanced electrochemical energy storage

Carbon nanotubes (CNTs) as superior support materials for functional nanoparticles (NPs) have been widely demonstrated. Nevertheless, the homogeneous loading of these NPs is still frustrated due to the inert surface of CNTs. In this work, a facile gas-phase pyrolysis strategy that the mixture of ferrocene and CNTs are confined in an isolated reactor with rising temperature is developed to fabricate a carbon-coated Fe₃O₄ nanoparticle/carbon nanotube (Fe₃O₄@C/CNT) composite. It is found the ultra-small Fe₃O₄ NPs (<10 nm) enclosed in a thin carbon layer are uniformly anchored on the surface of CNTs. These structural benefits result in the excellent lithium-ion storage performances of the Fe₃O₄@C/CNT composite. It delivers a stable reversible capacity of 861 mA·h·g⁻¹ at the current density of 100 mA·g⁻¹ after 100 cycles. The capacity retention reaches as high as 54.5% even at 6000 mA·g⁻¹. The kinetic analysis indicates that the featured structural modification improves the surface condition of the CNT matrix, and contributes to greatly decreased interface impendence and faster charge transfer. In addition, the post-morphology observation of the tested sample further confirms the robustness of the Fe₃O₄@C/CNT configuration.     

Double core---shell nanostructured Sn---Cu alloy as enhanced anode materials for lithium and sodium storage

Sn-based alloy materials are considered as a promising anode candidate for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), whereas they suffer from severe volume change during the discharge/charge process. To address the issue, double core–shell structured Sn–Cu@SnO₂@C nanocomposites have been prepared by a simple co-precipitation method combined with carbon coating approach. The double core–shell structure consists of Sn–Cu multiphase alloy nanoparticles as the inner core, intermediate SnO₂ layer anchored on the surface of Sn–Cu nanoparticle and outer carbon layer. The Sn–Cu@SnO₂@C electrode exhibits outstanding electrochemical performances, delivering a reversible capacity of 396 mA·h·g⁻¹ at 100 mA·g⁻¹ after 100 cycles for LIBs and a high initial reversible capacity of 463 mA·h·g⁻¹ at 50 mA·g⁻¹ and a capacity retention of 86% after 100 cycles, along with a remarkable rate capability (193 mA·h·g⁻¹ at 5000 mA·g⁻¹) for SIBs. This work provides a viable strategy to fabricate double core–shell structured Sn-based alloy anodes for high energy density LIBs and SIBs.     

Template-mediated strategy to regulate hierarchically nitrogen--sulfur co-doped porous carbon as superior anode material for lithium capacity

Considering its rapid lithiation/delithiation process and robust capacitive energy storage, hierarchical porous carbon is regarded as a promising candidate for lithium-ion batteries (LIBs). However, it remains a great challenge to construct a porous structure and prevent structure stacking for carbon-based materials. Herein, a template-mediated approach is developed to synthesize hierarchical nitrogen–sulfur co-doped porous carbon (NSPC) using low-cost asphalt precursors. The strategy for synthesis uses g-C₃N₄ and NaHCO₃ as gaseous templates and NaCl as a solid template, which causes the formation of hierarchical porous carbon with a high specific surface area. The resultant porous structure and nitrogen-doping process can prevent the aggregation of nanosheets, maintain the structural stability upon cycling, and achieve rate-capable lithium storage. Serving as a LIBs anode, reversible specific capacities of the NSPC24 electrode reach 788 and 280 mAh·g^–1 at 0.1 and 1 A·g^–1, respectively. Furthermore, its specific capacity remains at 830 mAh·g^–1 after 115 cycles at 0.1 A·g^–1. Even after 500 cycles, high specific capacities of 727 mAh·g^–1 at 0.5 A·g^–1 and 624 mAh·g^–1 at 1 A·g^–1 are achieved, demonstrating excellent cycling performance. The gas–solid bifunctional template-mediated approach can guide the design of porous materials very well, meanwhile realizing the high value-added utilization of asphalt.     

Controlled synthesis of Pt-loaded yolk–shell TiO2@SiO2 nanoreactors as effective photocatalysts for hydrogen generation

Yolk–shell and hollow structures are powerful platforms for controlled release, confined nanocatalysis, and optical and electronic applications. This contribution describes a fabrication strategy for a yolk–shell nanoreactor (NR) using a post decoration approach. The widely studied yolk–shell structure of silica-coated TiO₂ (TiO₂@SiO₂) was used as a model. At first, anatase TiO₂ spheres were prepared, and subsequently were given a continuous coating of carbonaceous and silica layers. Finally, the carbonaceous layer was removed to produce a yolk–shell structure TiO₂@SiO₂. By using an in-situ photodeposition method, Pt-encased spheres (Pt-TiO₂@SiO₂) were synthesized with Pt nanoparticles grown on the surface of the TiO₂ core, which contained void spaces suitable for use as NRs. The NR showed enhanced hydrogen production with a rate of 24.56 mmol·g⁻¹·h⁻¹ in the presence of a sacrificial agent under simulated sunlight. This strategy holds the potential to be extended for the synthesis of other yolk–shell photocatalytic NRs with different metal oxides.     

Three-dimensional sea urchin-like MnCo2O4 nanoarchitectures on Ni foam towards high-performance asymmetric supercapacitors

To construct supercapacitors (SCs) with high-efficient electrochemical properties, the morphology and structure of applied electrode materials are the key factors. Herein, three-dimensional (3D) sea urchin-like MnCo₂O₄ nanoarchitectures grown on Ni foam (NF) were successfully synthesized via a simple solvothermal method and subsequent annealing treatment. Electrochemical tests revealed that the area specific capacitances of the MnCo₂O₄ electrode and the corresponding assembled asymmetric device can achieve 1634 and 522 mF·cm⁻², respectively. When the power density of the assembled asymmetric supercapacitor (ASC) is 2.25 mW·cm⁻², the maximum energy density can reach 0.163 mW·h·cm⁻². After 5500 cycles of long-term stability test, the capacity retention rate maintains 91.7%. The excellent electrochemical performance can be mainly ascribed to the unique nanostructure of the material, which provides a great quantity of electroactive sites for Faraday redox reactions as well as accelerates the process of the ions/electrons transport. This work provides a certain reference value for the preparation of MnCo₂O₄ electrode with novel structure and excellent electrochemical performance for SCs.     

Ni-BTC/RGO复合材料的制备及其电化学性能EI北大核心CSCD

为了制备价格低廉且比电容高、循环稳定性好的电容器材料,采用电化学法合成石墨烯基含镍金属有机骨架材料Ni-BTC/RGO,研究含镍金属有机骨架材料Ni-BTC的合成条件以及Ni-BTC/RGO的电化学性能。对不同条件下的系列Ni-BTC材料进行XRD分析,并对Ni-BTC,RGO和Ni-BTC/RGO进行SEM测试、循环伏安测试和恒电流充放电测试。结果表明:工作电压为6 V、反应时间为3 h、反应体系温度为35℃是Ni-BTC的最佳合成条件;Ni-BTC和RGO成功复合且RGO对Ni-BTC的结构并未产生影响;复合材料主要表现赝电容电化学行为。在0.5 A·g^(-1)电流密度下,Ni-BTC/RGO的比电容为468.72 F·g^(-1),功率密度为0.249 W·g^(-1);在1.0 A·g^(-1)电流密度下循环500周次以后,比电容保留率为50.08%。     

Microwave hydrothermal synthesis of WO3(H2O)0.333/CdS nanocomposites for efficient visible-light photocatalytic hydrogen evolution

WO₃(H₂O)_0.333/CdS (WS) nanocomposites are obtained via a rapid microwave hydrothermal method, and they are served as visible light-driven photocatalysts for the H₂ generation. By using Pt as the cocatalyst, the WS nanocomposite with 70 wt.% CdS reaches the H₂ evolution rate of 10.32 mmol·g⁻¹·h⁻¹, much quicker than those of WO₃(H₂O)_0.333 and CdS. The cycling test reveals the good photocatalytic stability of the WS nanocomposite. The carrier transfer mechanism of WS nanocomposites can be explained by the Z-scheme mechanism. The existence of the Z-scheme heterojunction greatly helps to separate photogenerated carriers and thus improves the photocatalytic activity. The present work provides a rapid synthesis method for preparing Z-scheme heterojunction photocatalysts, and may be helpful for the green production of hydrogen.     

Preparation of sulfur-doped graphene fibers and their application in flexible fibriform micro-supercapacitors

A novel type of sulfur-doped graphene fibers (S-GFs) were prepared by the hydrothermal strategy, the in situ interfacial polymerization method and the annealing method. Two S-GFs were assembled into an all-solid-state fibriform micro-supercapacitor (micro-SC) that is flexible and has a high specific capacitance (4.55 mF·cm^-2) with the current density of 25.47 pA·cm^-2. The cyclic voltammetry (CV) curve of this micro-SC kept the rectangular shape well even when the scan rate reached 2 V·s^-1. There is a great potential for this type of S-GFs used in flexible wearable electronics.     

Preparation of porous sea-urchin-like CuO/ZnO composite nanostructure consisting of numerous nanowires with improved gas-sensing performance

A sea-urchin-like CuO/ZnO porous nanostructure is obtained via a simple solution method followed by a calcination process. There are abundant pores among the resulting nanowires due to the thermal decomposition of copper–zinc hydroxide carbonate. The specific surface area of the as-prepared CuO/ZnO sample is determined as 31.3 m²·g⁻¹. The gas-sensing performance of the sea-urchin-like CuO/ZnO sensor is studied by exposure to volatile organic compound (VOC) vapors. With contrast to a pure porous sea-urchin-like ZnO sensor, the sea-urchin-like CuO/ZnO sensor shows superior gas-sensing behavior for acetone, formaldehyde, methanol, toluene, isopropanol and ethanol. It exhibits a high response of 52.6–100 ppm acetone vapor, with short response/recovery time. This superior sensing behavior is mainly ascribed to the porous nanowire-assembled structure with abundant p–n heterojunctions.