Silver doped barium titanate nanoparticles for enhanced visible light photocatalytic degradation of dyes

Due to the rapid growth of global population, new, fast and reliable methods must be developed to purify contaminated water. Various photocatalysts have been developed to remove organic dyes from water. Herein, Ag doped BaTiO3 has been synthesized using a facile solvothermal method and its excellent photocatalytic activities were demonstrated in degradation of both anionic and cationic dyes under visible light illumination. Ag doped BaTiO3 nanoparticles showed greater efficacy in the degradation of methylene blue (MB) and eosin yellow (EY) than undoped BaTiO3 nanoparticles, which makes them a better candidate for photocatalysis. 1.0 AgBT sample showed the highest photocatalytic activity for MB (99.1 % in 100 min) and EY (99.3 % in 60 min) dye degradation compared with those of other samples. Further, the trapping experiments revealed that hydroxyl radicals and holes are the active species in the photocatalytic process of MB and EY dye degradation and recycle test showed excellent stability of the synthesized material.

Recent Research of NiCo2O4/Carbon Composites for Supercapacitors

Supercapacitors have played an important role in electrochemical energy storage. Recently, researchers have found many effective methods to improve electrode materials with more robust performances through the increasing volume of scientific publications in this field. Though nickel cobaltite (NiCo2O4), as a promising electrode material, has substantially demonstrated potential properties for supercapacitors, its composites usually show much better performances than the pristine NiCo2O4. The combination of carbon-based materials and NiCo2O4 has been implemented recently due to the dual mechanisms for energy storage and the unique advantages of carbon materials. In this paper, we review the recent research on the hybrids of NiCo2O4 and carbon nanomaterials for supercapacitors. Typically, we focused on the reports related to the composites containing graphene (or reduced graphene oxide), carbon nanotubes, and amorphous carbon, as well as the major synthesis routes and electrochemical performances. Finally, the prospect for the future work is also discussed.

Vanadium nitride nanoparticle decorated N-doped carbon nanotube/N-doped carbon nanosheet hybrids via a C3N4 self-sacrificing method for electrochemical capacitors

Owing to the wide negative potential window (∼1.2 V) along with high specific capacitance (1340 F g-1) in alkaline electrolyte, vanadium nitride (VN) has been served as promising negative supercapacitor electrode material. However, VN is easy to dissolve during cycling process and shows low capacitance retainability. Herein, a hybrid electrode (marked as VN/NCNT/NCN), featuring VN nanoparticles and N-doped carbon nanotube inserted in N-doped carbon nanosheets, has been fabricated with a facile C3N4 self-sacrificing method. The porous structure and high conductive carbon skeleton, as well as the uniform distribution of VN nanoparticles give VN/NCNT/NCN a great amount of active site and fulfill excellent electrochemical performance for VN/NCNT/NCN-based electrode. The as-fabricated hybrid electrode exhibits a maximum specific capacitance of 232.9 F g-1 at 1 A g-1. Moreover, the cycling performance has been greatly improved and the specific capacitance remains 91% after 5000 cycles.

POM-derived MoO3/CoMoO4 mixed oxides directed by glucose for high-performance supercapacitors

Facile synthesis of MoO3/CoMoO4 composites derived from polyoxometalate using a sacrificial template for high performance supercapacitors.

Facile fabrication of carbon-coated spinel nickel–cobalt–sulfide hollow spheres to achieve high-performance supercapacitors

This paper presents a simple method to prepare carbon-coated spinel nickel–cobalt–sulfide metal hollow spheres with excellent electrochemical properties.

Rhodium doping augments photocatalytic activity of barium titanate: effect of electronic structure engineering

Environmentally friendly BaTiO3 is emerging as a potential photocatalyst due to its tunable electronic structure. Although originally believed to be a poor photocatalyst due to its wide band gap, several strategies have been implemented to reduce its band gap. One such approach is doping, but this often leads to the formation of mid gap recombination centers and diminishes the efficiency of the material. In the present work, we study for the first time the effect of site occupancy of Rh on the electronic structure of BaTiO3. As the theoretical results reveal that if Rh occupies both Ba and Ti sites simultaneously it leads to the formation of mid gap states, an experimental approach is implemented to reduce the band gap of BaTiO3 while simultaneously avoiding the formation of recombination centers. The facile one pot hydrothermal approach reported here directs the Rh towards Ba sites leading to a decrease in the band gap due to the appearance of donor Rh3+ states, suppressing the formation of Rh4+ states. A promising photocatalytic activity of 96% degradation of methylene blue dye in 120 minutes was observed for the 0.5 Rh sample indicating the high efficiency of the material.

The key role of microscopic structure and graphene sheet-high homogenization in the high rate capability and cycling stability of Ni-Co LDH

As a typical electrode material in Faraday supercapacitors (FSs), Ni(OH)2 has some intrinsic issues such as low electrical conductivity and structural instability, resulting in its low performance. In view of these issues, we design a multifunctional nanostructure, rigid nanosheet-interlaced structure of Ni-Co LDH/graphene to improve the electrical conductivity and structural stability of Ni(OH)2. Under the high shear applied by a high shear mixer (HSM) and the regulation of polyvinylpyrrolidone (PVP), the designed structure is realized. Benefitting from the well-designed structure and improved electrical conductivity of the graphene sheet-high homogenization, Ni-Co LDH/graphene presents the expected performance. It exhibits a high specific capacity of 1020 C g-1 at a low current density of 2.7 A g-1 and excellent high rate performance (637.5 C g-1 at 62.5 A g-1). The asymmetrical supercapacitors (ASCs) assembled with the composite as the positive material show high energy density (86.5 W h kg-1 at a power density of 695.7 W kg-1). Due to the improved structural stability, the ASCs also exhibit high cycling stability (a capacity retention of 97.8% after 10 000 charge-discharge cycles).

Encapsulation of Co3 O4 Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co₃ O₄ nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co₃ O₄ nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co₃ O₄ nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g^-1 (2760 F g^-1 ) at current density 2 A g^-1 , which is greater than pristine Co₃ O₄ @NF (1045.8 C g^-1 or 2324 F g^-1 ). The rate capability with 5 nm NiO/Co₃ O₄ @NF nanocone structures is about 77% whereas Co₃ O₄ @NF retains 46 % of capability at 10 A g^-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co₃ O₄ @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg^-1 (4268 W kg^-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

A porous graphene-NiFe2O4 nanocomposite with high electrochemical performance and high cycling stability for energy storage applications

It is well agreed that supercapacitors form an important class of energy storage devices catering to a variety of needs. However, designing the same using eco-friendly and earth abundant materials with high performance is still the dire need of the day. Here, we report a facile solvothermal synthesis of a porous graphene-NiFe2O4 (PGNF) nanocomposite. Thorough elemental, diffraction, microscopic and spectroscopic studies confirmed the formation of the PGNF composite, in which the NF nanoparticles are covered over the PG surface. The obtained 10 PGNF composite showed a surface area of 107 m2 g-1, with large pore volume which is favorable for charge storage properties. When utilizing the material as an electrode for a supercapacitor in a 2 M KOH aqueous electrolyte, the electrode displayed an impressive specific capacitance value of 1465.0 F g-1 at a scan rate of 5 mV s-1 along with a high capacitance retention of 94% after 10 000 discharge cycles. The fabricated symmetrical supercapacitor device exhibited an energy density of 4.0 W h kg-1 and a power density of 3600.0 W kg-1 at a high applied current density of 14 A g-1. The superior electrochemical performance is attributed to the synergetic effect of the composite components which not only provided enough electroactive channels for the smooth passage of electrolyte ions but also maintained the hybrid structure intact in the ongoing electrochemical process. The obtained results underpin the promising utility of this material for future electrochemical energy storage devices.