S or N-monodoping and S,N-codoping effect on electronic structure and electrochemical performance of tin dioxide: Simulation calculation and experiment validation

In Situ Self-Assembly of Nitrogen-Doped 3D Flower-like Hierarchical Porous Carbon and Its Application for Supercapacitors

The hierarchical porous carbon-based materials derived from biomass are beneficial for the enhancement of electrochemical performances in supercapacitors. Herein, we report the fabrication of nitrogen-doped 3D flower-like hierarchical porous carbon (NPC) assembled by nanosheets using a mixture of urea, ZnCl2, and starch via a low-temperature hydrothermal reaction and high-temperature carbonization process. As a consequence, the optimized mass ratio for the mixture is 2:2:2 and the temperature is 700 °C. The NPC structures are capable of electron transport and ion diffusion owing to their high specific surface area (1498.4 m2 g-1) and rich heteroatoms. Thereby, the resultant NPC electrodes display excellent capacitive performance, with a high specific capacitance of 249.7 F g-1 at 1.0 A g-1 and good cycling stability. Remarkably, this implies a superior energy density of 42.98 Wh kg-1 with a power density of 7500 W kg-1 in organic electrolyte for the symmetrical supercapacitor. This result verifies the good performance of as-synthesized carbon materials in capacitive energy storage applications, which is inseparable from the hierarchical porous features of the materials.

Visible light photocatalytic properties of one-step SnO2-templated grown SnO2/SnS2heterostructure and SnS2nanoflakes

The nanoflakes of SnS₂/SnO₂heterostructure and SnS₂were synthesized by a one-step SnO₂-templated chemical vapor deposition method. The metal oxide-assisted growth mechanism of SnS₂/SnO₂heterostructure and SnS₂nanoflakes were realized through investigating serial microstructures of products with varied growth time. Furthermore, the photocatalytic activity for MB dyes degradation of varied growth time products was used to explore the effect of product microstructure under the visible light irradiation. The SnO₂/SnS₂heterostructure and the oxide vacancies of nanoflakes demonstrated an improved visible light photocatalytic performance for MB degradation, which was around twice of the pure SnS₂nanoflakes and better than P25. The results of different scavengers on the degradation efficiency for MB indicate the·O₂^-, and ·OH are the main active species in the photodegradation reaction. The one-step growth mechanism of SnS₂/SnO₂could prove a facile process to grow metal oxide-metal sulfide heterostructure.

Synthesis and electrochemical performance of an electroactive nitrogen-doping SnO2 nanoarray supported on carbon fiber

An electroactive nitrogen-doping tin dioxide nanorod array (N-SnO2 NRA) is designed as an effective energy-storage electrode material for supercapacitor applications. N-SnO2 supported on a carbon fiber substrate is prepared using SnCl4 as a precursor through hydrolysis, hydrothermal growth, and an NH3-nitriding process. Electroactive N-SnO2 is formed by an N-doping reaction between Sn(OH)4 and NH3, revealing a high nitrogen-doping level of 12.5% in N-SnO2. N-SnO2/carbon fiber reveals a lower ohmic resistance and charge transfer resistance than SnO2/carbon fiber, which is consistent with its higher current response and lower voltage drop in electrochemical measurements. N-SnO2 NRA has an independent nanoarray structure and a small side length of a quadrangular nanorod, contributing to a more accessible interspace, reactive sites, and feasible electrolyte ion diffusion. The N-SnO2/carbon fiber NRA electrode shows higher specific capacitance (105.4 F g−1 at 0.5 A g−1) and rate capacitance retention (45.0% from 0.5 to 5 A g−1) than a SnO2/carbon fiber NRA electrode (58.6 F g−1, 38.4%). Significantly, the cycling capacitance retention after 2000 cycles increases from 78.1% of SnO2/carbon fiber to 98.8% of N-SnO2/carbon fiber, presenting a superior electrochemical cycling stability. The N-SnO2 supercapacitor maintains stable power working at an output voltage of 1.6 V. The specific capacitance decreases from 75.2 to 55.1 F g−1 when the current density increases from 1 to 10 A g−1. The corresponding energy density decreases from 24.23 to 9.81 Wh kg−1, presenting a reasonable rate capability. So, the prepared N-SnO2 nanorod array demonstrates superior capacitance performance for energy-storage applications.

Electrochemical performance of the homologous molybdenum(vi) redox-active gel polymer electrolyte system

PVA–H₃PO₄–Na₂MoO₄ and PVA–H₃PO₄–PMo₁₂ are assembled into a single solid-state supercapacitor to improve the specific capacitance. Homologous molybdenum (vi) of PMo₁₂ and Na₂MoO₄ provides synergistic effect to improve faradaic capacitance performance.

Fabrication of Highly Ordered Ag/TiO2 Nanopore Array as a Self-Cleaning and Recycling SERS Substrate

Silver nanoparticles deposited on a titania nanopore array (Ag/TiO2 NPA) has been designed as a surface-enhanced Raman scattering (SERS) substrate for sensitive and recycling application of organic molecule detection. A TiO2 NPA was fabricated by a surface oxidization reaction of a titanium sheet by a double anodization process. A Ag/TiO2 NPA was then formed by depositing silver nanoparticles onto the TiO2 NPA by a cycling chemical reduction deposition process. The Ag/TiO2 NPA has a uniform mono-layer dispersion of Ag nanoparticles with a size of 30–50 nm on TiO2 nanopores with a diameter of 100–110 nm. The Ag/TiO2 NPA SERS substrate could facilitate interfacial adsorption of Rhodamine 6G (R6G), which achieves a sensitive detection limit of 10−8 M R6G through SERS spectrum measurement. The Ag/TiO2 NPA SERS substrate achieves an analytical enhancement factor value of 2.6 × 105. The Ag/TiO2 NRA could promote the UV light-excited photocatalytic degradation reaction of R6G adsorbed on its surface which gives rise to a refreshed Ag/TiO2 NRA under UV irradiation for 60 min and accordingly behave as a self-cleaning and recycling SERS substrate. The Ag/TiO2 NPA exhibits a much higher R6G degradation reaction rate constant (0.05764 min−1) than the TiO2 NPA (0.02600 min−1), indicating its superior photocatalytic activity and self-cleaning activity. The refreshed Ag/TiO2 NPA was able to be recycled for the Raman detection of R6G, maintaining a high stability, reproducibility, and cyclability. The highly ordered Ag/TiO2 NPA with well controlled Ag nanoparticle dispersion and TiO2 nanopore shape could act as a suitable SERS substrate for recycling and self-cleaning application for stable and sensitive molecule detection.

Fabrication and charge storage capacitance of PPY/TiO2/PPY jacket nanotube array

A PPY/TiO2/PPY jacket nanotube array was fabricated by coating PPY layer on the external and internal surface of a tube wall-separated TiO2 nanotube array. It shows coaxial triple-walled nanotube structure with two PPY nanotube layers sandwiching one TiO2 nanotube layer. PPY/TiO2/PPY reveals much higher current response than TiO2. The theoretical calculation indicates PPY/TiO2/PPY reveals higher density of states and lower band gap, accordingly presenting higher conductivity and electroactivity, which is consistent with the experimental result of a higher current response. The electroactivity is highly enhanced in H2SO4 rather than Na2SO4 electrolyte due to feasible pronation process of PPY in an acidic solution. PPY/TiO2/PPY could conduct the redox reaction in H2SO4 electrolyte which involves the reversible protonation/deprotonation and HSO4 − doping/dedoping process and accordingly contributes to Faradaic pseudocapacitance. The specific capacitance is highly enhanced from 1.7 mF cm−2 of TiO2 to 123.4 mF cm−2 of PPY/TiO2/PPY at 0.1 mA cm−2 in H2SO4 electrolyte. The capacitance also declines from 123.4 to 31.7 mF cm−2 when the current density increases from 0.1 to 1 mA cm−2, presenting the rate capacitance retention of 26.7% due to the semiconductivity of TiO2. A PPY/TiO2/PPY jacket nanotube with high charge storage capacitance is regarded as a promising supercapacitor electrode material.

Facile Synthesis of Co3O4-Incorporated Multichannel Carbon Nanofibers for Electrochemical Applications

Considering their superior electrochemical performances, extensive studies have been carried out on composite nanomaterials based on porous carbon nanofibers. However, the introduction of inorganic components into a porous structure is complex and has a low yield. In this study, we propose a simple synthesis of cobalt-oxide-incorporated multichannel carbon nanofibers (P-Co-MCNFs) as electrode materials for electrochemical applications. The cobalt oxide component is directly formed in the carbon structure by a simple oxygen plasma exposure of the phase-separated polymer nanofibers. P-Co-MCNF displays high specific capacitance (815 F g^-1 at 2.0 A g^-1), rate capability (821 F g^-1 at 1 A g^-1 and 786 F g^-1 at 20 A g^-1), and cycle stability (92.1% for 5000 cycles) as a supercapacitor electrode. Moreover, excellent sensitivity (down to 1 nM) and selectivity to the glucose molecule is demonstrated for nonenzyme sensor applications.

Electrochemical performance of activated carbon fiber with hydrogen bond-induced high sulfur/nitrogen doping

The sulfur/nitrogen co-doped activated carbon fiber (S/N-ACF) is prepared by the thermal treatment of thiourea-bonded hydroxyl-rich carbon fiber, which can bond the decomposition products of thiourea through hydrogen bond interaction to avoid the significant loss of sulfur and nitrogen sources during the thermal treatment process. The sulfur/nitrogen co-doped carbon fiber (S/N-CF) is prepared by the thermal treatment of thiourea-adsorbed carbon fiber. The doping degree of the carbon fiber is improved by reasonable strategy. S/N-ACF shows a higher amount of S/N doping (4.56 at% N and 3.16 at% S) than S/N-CF (1.25 at% N and 0.61 at% S). S/N-ACF with high S/N doping level involves highly active sites to improve the capacitive performance, and high delocalization electron to improve the conductivity and rate capability when compared with the normal S/N co-doped carbon fiber (S/N-CF). Accordingly, the specific capacitance increases from 1196 mF cm⁻² for S/N-CF to 2704 mF cm⁻² for S/N-ACF at 1 mA cm⁻². The all-solid-state flexible S/N-ACF supercapacitor achieves 184.7 μW h cm⁻² at 350 μW cm⁻². The results suggest that S/N-ACF has potential application as a CF-based supercapacitor electrode material.

Sulfur/nitrogen co-doped activated carbon fiber is prepared by thermal treatment of thiourea-bonded hydroxyl-rich carbon fiber, which achieves high doping level and electrochemical performance.