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.     

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.     

LaNiO3 modified with Ag nanoparticles as an efficient bifunctional electrocatalyst for rechargeable zinc--air batteries

No-precious bifunctional catalysts with high electrochemical activities and stability were crucial to properties of rechargeable zinc–air batteries. Herein, LaNiO₃ modified with Ag nanoparticles (Ag/LaNiO₃) was prepared by the co-synthesis method and evaluated as the bifunctional oxygen catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with LaNiO₃, Ag/LaNiO₃ demonstrated the enhanced catalytic activity towards ORR/OER as well as higher limited current density and lower onset potential. Moreover, the potential gap between ORR potential (at −3 mA·cm⁻²) and OER potential (at 5 mA·cm⁻²) was 1.16 V. The maximum power density of the primary zinc–air battery with Ag/LaNiO₃ catalyst achieved 60 mW·cm⁻². Furthermore, rechargeable zinc–air batteries operated reversible charge–discharge cycles for 150 cycles without noticeable performance deterioration, which showed its excellent bifunctional activity and cycling stability as oxygen electrocatalyst for rechargeable zinc–air batteries. These results indicated that Ag/LaNiO₃ prepared by the co-synthesis method was a promising bifunctional catalyst for rechargeable zinc–air batteries.     

Mn-doped perovskite-type oxide LaFeO3 as highly active and durable bifunctional electrocatalysts for oxygen electrode reactions

Perovskite oxides based on the alkaline earth metal lanthanum for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes are promising catalysts, but their catalytic activity and stability remain unsatisfactory. Here, we synthesized a series of LaFe_1−xMn_xO₃ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) perovskite oxides by doping Mn into LaFeO₃ (LF). The results show that the doping amount of Mn has a significant effect on the catalytic performance. When x = 0.5, the catalyst LaFe_0.5Mn_0.5O₃ (LFM) exhibits the best performance. The limiting current density in 0.1 mol·L⁻¹ KOH solution is 7 mA·cm⁻², much larger than that of the commercial Pt/C catalyst (5.5 mA·cm⁻²). Meanwhile, the performance of the doped catalyst is also superior to that of commercial Pt/C in terms of the long-term durability. The excellent catalytic performance of LFM may be ascribed to its abundant O²⁻/O⁻ species and low charge transfer resistance after doping the Mn element.     

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.     

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.     

Size-constrained ultrathin BiOCl nanosheets@C composites with enhanced photocatalytic and photoelectrochemical performance

Size-constrained ultrathin BiOCl nanosheets@C composites were achieved by one-step hydrothermal route. It was found that the carbon coated on the surface of BiOCl nanosheets not only accelerated the separation of electrons and holes, but also restricted the outward growth of the BiOCl crystal structure to expose more active catalytic sites. In addition, the obtained composites have stable and close interface contact, beneficial for the structural stability of products as well as the rapid charge transfer. The average sheet thickness was in the range of 20–60 nm. Compared with the ability for pure BiOCl to degrade RhB, the degradation rate of the optimal composite can reach 100% within 15 min, while the corresponding photocurrent intensity could reach 5.6 μA·cm⁻², and its impedance value was also the smallest. The removal experiments of active substances showed that h⁺ and ∙O₂⁻ play important roles in the process of photocatalytic degradation. It can be expected that the resulted composites in this work can be used as potential materials for photocatalytic and photoelectrochemical applications.     

Fe-doped NiCo2O4 hollow hierarchical sphere as an efficient electrocatalyst for oxygen evolution reaction

We prepared porous Fe-doped nickel cobaltate (Fe-NiCo₂O₄) hollow hierarchical nanospheres through a facile self-templated synthetic strategy. Due to the porous hollow structure and composition, the Fe-NiCo₂O₄ presented vastly superior electrocatalytic activity for the oxygen evolution reaction (OER), compared with NiCo₂O₄ and the majority of other OER catalysts. With an aim of stimulating a current density of 10 mA·cm⁻², the Fe-NiCo₂O₄ catalyst needs an overpotential of 210 mV, which is on a par with the general properties of commercial IrO₂. In addition, the Fe-NiCo₂O₄ catalyst performed stably in long-term testing. The excellent activity and long-term stability showed that such catalysts have great promise for widespread application in the field of water splitting.     

Facile solvothermal synthesis of NiFe2O4 nanoparticles for high-performance supercapacitor applications

We report a green and facile approach for the synthesis of NiFe₂O₄ (NF) nanoparticles with good crystallinity. The prepared materials are studied by various techniques in order to know their phase structure, crystallinity, morphology and elemental state. The BET analysis revealed a high surface area of 80.0 m²·g⁻¹ for NF possessing a high pore volume of 0.54 cm³·g⁻¹, also contributing to the amelioration of the electrochemical performance. The NF sample is studied for its application in supercapacitors in an aqueous 2 mol·L⁻¹ KOH electrolyte. Electrochemical properties are studied both in the three-electrode method and in a symmetrical supercapacitor cell. Results show a high specific capacitance of 478.0 F·g⁻¹ from the CV curve at an applied scan rate of 5 mV·s⁻¹ and 368.0 F·g⁻¹ from the GCD analysis at a current density of 1 A·g⁻¹ for the NF electrode. Further, the material exhibited an 88% retention of its specific capacitance after continuous 10000 cycles at a higher applied current density of 8 A·g⁻¹. These encouraging properties of NF nanoparticles suggest the practical applicability in high-performance supercapacitors.     

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.     

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.     

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.     

Light-switchable catalytic activity of Cu for oxygen reduction reaction

The surface reactivity of metals is fundamentally dependent on the local electronic structure generally tailored by atomic compositions and configurations during the synthesis. Herein, we demonstrate that Cu, which is inert for oxygen reduction reaction (ORR) due to the fully occupied d-orbital, could be activated by applying a visible-light irradiation at ambient temperature. The ORR current is increased to 3.3 times higher in the potential range between −0.1 and 0.4 V under the light of 400 mW·cm⁻², and the activity enhancement is proportional to the light intensity. Together with the help of the first-principle calculation, the remarkably enhanced electrocatalytic activity is expected to stem mainly from the decreased metal–adsorbate binding by photoexcitation. This finding provides an additional degree of freedom for controlling and manipulating the surface reactivity of metal catalysts besides materials strategy.     

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.     

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.     

Preparation and thermal properties of layered porous carbon nanotube/epoxy resin composite films

A floating-catalyst spray pyrolysis method was used to synthesize carbon nanotube (CNT) thin films. With the use of ammonium chloride as a pore-former and epoxy resin (EP) as an adhesive, CNT/EP composite films with a porous structure were prepared through the post-heat treatment. These films have excellent thermal insulation (0.029--0.048 W·m⁻¹·K⁻¹) at the thickness direction as well as a good thermal conductivity (40--60 W·m⁻¹·K⁻¹) in the film plane. This study provides a new film material for thermal control systems that demand a good thermal conductivity in the plane but outstanding thermal insulation at the thickness direction.     

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.     

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.     

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.     

Microwave hydrothermal synthesis of lanthanum oxyfluoride nanorods for photocatalytic nitrogen fixation: Effect of Pr doping

Photocatalytic fixation of nitrogen has been recognized as a green and promising strategy for ammonia synthesis under ambient conditions. However, the efficient reduction of nitrogen remains a challenge due to high activation energy of nitrogen and low utilization of solar energy. Herein, lanthanum oxyfluoride with different doping content of Pr³⁺ (LaOF:xPr³⁺) upconversion nanorods were synthesized by microwave hydrothermal method. Results indicated that the doping of Pr³⁺ generated considerable defects on the surface of LaOF which acted as the adsorption and activation center for nitrogen. Meanwhile, the Pr³⁺ ion narrowed the band gap and broadened the light response range of LaOF because LaOF:Pr³⁺ can upconvert visible light into ultraviolet light, which excite LaOF nanorods and improve the utilization of solar light. The doping amount of Pr³⁺ had critical effect on the photocatalytic nitrogen fixation performance which reached as high as 180 μmol·L⁻¹·h⁻¹ when the molar ratio of Pr³⁺ to LaOF was optimized to be 2%.