In-situ formation of mesoporous SnO2@C nanocomposite electrode for supercapacitors

Hydrothermal synthesis and electrochemical properties of Sn-based peanut shell biochar electrode materials

Using activated-carbon-based electrodes derived from waste biomass in super-capacitor energy technologies is an essential future strategy to achieve sustainable energy and environmental protection. Biomass feed-stocks such as bamboo and straw have been used to prepare activated carbon-based electrodes. This experiment used peanut shells (waste biomass) as carbon precursors. Peanut shell-activated biochar materials were prepared using KOH activation and heat treatment, and SnO2@KBC-CNTs, a composite electrode material of biochar loaded with tin oxide. It was produced through hydrothermal synthesis, utilizing SnCl4-5H2O as the tin precursor. The application of KOH activators during pyrolysis markedly enhanced the porosity and specific surface area of the resultant activated biochar, due to effective dispersion and degradation of pyrolytic products. Characterized by a micro-mesoporous structure, the composite's pores boasted a specific surface area of 158.69 m2 g-1. When tested at a density of current of 0.5 A g-1, the specific capacitance of SnO2@KBC-CNTs reached 198.62 F g-1, nearly doubling the performance of the KBC electrode material alone. Moreover, the composite demonstrated a low ion transfer resistance of 0.71 Ω during charge-discharge cycles.

Anodic SnO2 Nanoporous Structure Decorated with Cu2O Nanoparticles for Sensitive Detection of Creatinine: Experimental and DFT Study

Advanced anodic SnO₂ nanoporous structures decorated with Cu₂O nanoparticles (NPs) were employed for creatinine detection. Anodization of electropolished Sn sheets in 0.3 M aqueous oxalic acid electrolyte under continuous stirring produced complete open top, crack-free, and smooth SnO₂ nanoporous structures. Structural analyses confirm the high purity of rutile SnO₂ with successful functionalization of Cu₂O NPs. Morphological studies revealed the formation of self-organized and highly-ordered SnO₂ nanopores, homogeneously decorated with Cu₂O NPs. The average diameter of nanopores is ∼35 nm, while the average Cu₂O particle size is ∼23 nm. Density functional theory results showed that SnO₂@Cu₂O hybrid nanostructures are energetically favorable for creatinine detection. The hybrid nanostructure electrode exhibited an ultra-high sensitivity of around 24343 μA mM^-1 cm^-2 with an extremely lower detection limit of ∼0.0023 μM, a fast response time (less than 2 s), and wide linear detection ranges of 2.5-45 μM and 100 μM to 15 mM toward creatinine. This is ascribed to the creation of highly active surface sites as a result of Cu₂O NP functionalization, SnO₂ band gap diminution, and the formation of heterojunction and Cu(1)/Cu(ll)-creatinine complexes through secondary amines which occur in the creatinine structure. The real-time analysis of creatinine in blood serum by the fabricated electrode evinces the practicability and accuracy of the biosensor with reference to the commercially existing creatinine sensor. The proposed biosensor demonstrated excellent stability, reproducibility, and selectivity, which reflects that the SnO₂@Cu₂O nanostructure is a promising candidate for the non-enzymatic detection of creatinine.

Hierarchical Porous Heteroatoms-Co-Doped Activated Carbon Synthesized from Coconut Shell and Its Application for Supercapacitors

Coconut husk biomass waste was used as the carbon precursor to develop a simple and economical process for the preparation of hierarchical porous activated carbon, and the electrochemical properties of the electrode material were explored. The important process variables of carbonization, the weight ratios of the coconut shell/KOH, the amount of source dopant, and the carbonization temperature were investigated in order to reveal the influence of the as-obtained microporous/mesoporous/macroporous hierarchical porous carbon materials on the powder properties. Using a BET specific surface area analyzer, Raman analysis, XPS and SEM, surface morphology, pore distribution and specific surface area of the hierarchical porous carbon materials are discussed. The results show that the as-prepared N-, S- and O-heteroatom-co-doped activated carbon electrode was manufactured at 700 °C for electrochemical characteristics. The electrochemical behavior has the characteristics of pseudo-capacitance, and could reach 186 F g^-1 at 1 A g^-1 when measured by the galvanostatic charge-discharge (GCD) test. After 7000 cycles of the charge-discharge test, the initial capacitance value retention rate was 95.6%. It is predicted that capacitor materials made when using coconut shell as a carbon source will have better energy storage performance than traditional carbon supercapacitors.

Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Metal oxide heterostructures have gained huge attention in the energy storage applications due to their outstanding properties compared to pristine metal oxides. Herein, magnetic Fe₂O₃@SnO₂ heterostructures were synthesized by the sol-gel electrospinning method at calcination temperatures of 450 and 600 °C. XRD line profile analysis indicated that fraction of tetragonal tin oxide phase compared to rhombohedral hematite was enhanced by increasing calcination temperature. FESEM images revealed that hexagonal nanoplatelets of Fe₂O₃ were hierarchically anchored on SnO₂ hollow nanofibers. Optical band gap of heterogeneous structures was increased from 2.06 to 2.40 eV by calcination process. Vibrating sample magnetometer analysis demonstrated that increasing calcination temperature of the samples reduces saturation magnetization from 2.32 to 0.92 emu g^-1. The Fe₂O₃@SnO₂-450 and Fe₂O₃@SnO₂-600 nanofibers as active materials coated onto Ni foams (NF) and their electrochemical performance were evaluated in three and two-electrode configurations in 3 M KOH electrolyte solution. Fe₂O₃@SnO₂-600/NF electrode exhibits a high specific capacitance of 562.3 F g^-1 at a current density of 1 A g^-1 and good cycling stability with 92.8% capacitance retention at a high current density of 10 A g^-1 after 3000 cycles in three-electrode system. The assembled Fe₂O₃@SnO₂-600//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 50.2 Wh kg^-1 at a power density of 650 W kg^-1. The results display that the Fe₂O₃@SnO₂-600 can be a promising electrode material in supercapacitor applications.

Tetra germanium nonaselenide enwrapped with reduced graphene oxide and functionalized carbon nanotubes (Ge4Se9/RGO/FCNTs) hybrids for improved energy storage performances

The development of multifunctional layered semiconductor materials and their carbonaceous hybrids as acceptable positive electrode materials for supercapacitor application is of key interest. Ternary germanium selenide (Ge₄Se₉) with reduced graphene oxide (RGO) and functionalized carbon nanotube (FCNT) hybrids were successfully synthesized by following a one-step hydrothermal approach, and their electrochemical energy storage performance toward supercapacitor (SC) applications was investigated. It was observed that the specific capacitance of Ge₄Se₉/RGO/FCNTs was 440 F g^-1 at 1 A g^-1 in an acidic (1 M H₂SO₄) medium. Further, the material showed 83% retention of its own initial value of capacitance with 98% coulombic efficiency after 5000 galvanostatic charge-discharge cycles. Considering the two-dimensional (2D) layered structures of MXenes with their greater stability, exceptional hydrophilicity, and pseudocapacitive behavior in aqueous electrolytes makes them an alternative for the fabrication of asymmetric SC devices. The above findings about MXenes suggest the design of an asymmetric device using MXene as the negative electrode material and as-prepared Ge₄Se₉/RGO/FCNTs as the positive electrode material in a similar electrolyte media. The fabricated Ge₄Se₉/RGO/FCNTs//MXenes displayed a higher specific capacitance of 102 F g^-1 at 1 A g^-1, with an acceptable energy density (E.D.) of 32 W h kg^-1 and a power density (P.D.) of 1071 W kg^-1. Furthermore, over long-term repeated 5000 GCD cycles the fabricated device retained 92% of its initial capacitance and good reversibility (96% coulombic efficiency), making the Ge₄Se₉/RGO/FCNT//MXenes assembly a preferable electrode material for enhancing asymmetric SC performance.

Tin oxide based nanostructured materials: synthesis and potential applications

In view of their inimitable characteristics and properties, SnO₂ nanomaterials and nanocomposites have been used not only in the field of diverse advanced catalytic technologies and sensors but also in the field of energy storage such as lithium-ion batteries and supercapacitors, and in the field of energy production such as solar cells and water splitting. This review discusses the various synthesis techniques such as traditional methods, including processes like thermal decomposition, chemical vapor deposition, electrospinning, sol-gel, hydrothermal, solvothermal, and template-mediated methods and green methods, which include synthesis through plant-mediated, microbe-mediated, and biomolecule-mediated processes. Moreover, the advantages and limitations of these synthesis procedures and how to overcome them that would lead to future research are also discussed. This literature also focuses on various applications such as environmental remediation, energy production, energy storage, and removal of biological contaminants. Therefore, the rise and journey of SnO₂-based nanocomposites will motivate the modern generation of chemists to modify and design robust nanoparticles and nanocomposites that can effectively tackle significant environmental challenges. This overview concludes by providing future perspectives on research into tin oxide in synthesis and its various applications.

Study on the Crystallinity and Oxidation States of Nanoporous Anodized Tin Oxide Films Regulated by Annealing Treatment for Supercapacitor Application

In this study, electrodeposition combined with anodization was employed to prepare a nanoporous tin oxide film on a pure copper substrate. It was found that annealing temperature played a critically significant role in regulating the crystallinity, pore size, and contents of different oxidation states of the anodized tin oxide film to affect the electrochemical performance. The study verified that SnO_x films treated by optimized annealing at 500 °C with precisely controlling the nanoporous morphology and crystallinity displayed competitive specific capacitance at an appropriate ratio of Sn⁴⁺ to Sn²⁺. A maximum specific capacitance of 86.2 mF/cm² could be achieved at this temperature, and the capacitance retention rate still exceeded 90% even after 8000 charge-discharge cycles. With properly designed annealing treatment, we implemented tin film anodization to obtain an optimized electrode with significantly enhanced electrochemical performance, which shows a promising application in the electrochemical field to prepare electrodes.

Preparation and Properties of an Ultrahigh-Energy-Density Aqueous Supercapacitor with a Superconcentrated Electrolyte and a Sr-Modified Lanthanum Zirconate Flexible Electrode

Although supercapacitors are considered to play a vital role in flexible electronic devices, there are still some problems that need to be overcome, such as low energy density and narrow electrochemical stability windows in aqueous electrolytes. Herein, we have successfully synthesized a series of Sr-modified La₂Zr₂O₇ (LZO-x) nanofibers as a new electrode material by a facile electrospinning technique. To determine the best doping sample, the changes in structures and electrochemical performances of La₂Zr₂O₇ (LZO-x) nanofibers with various Sr contents are investigated carefully. Then, the LZO-0.2 sample shows the highest capacitance (1445 mF·cm^-2). Furthermore, we also develop a low-cost superconcentrated electrolyte, which achieves a wide electrochemical stability window of 2.7 V using a working electrode (LZO-0.2). Finally, we use the LZO-0.2 electrode and the superconcentrated electrolyte to fabricate a flexible supercapacitor device, which shows an excellent capacitance of 175 F·g^-1 at a current density of 1.15 A·g^-1. Moreover, the aqueous device has excellent cycle stability and outstanding flexibility, and the energy density of this device is 177.2 Wh·kg^-1 and the corresponding power density is 1557.7 W·kg^-1.

Tin-based metal-phosphine complexes nanoparticles as long-cycle life electrodes for high-performance hybrid supercapacitors

New tin-based metal-phosphine complexes of [Sn(OH)₄(PPh₃)₂] and [Sn(OH)₂(PPh₃)₂] have been successfully synthesized and used as supercapacitor electrodes for the first time, exhibiting a high specific capacitance, a good rate capability, and an excellent cycling stability. The specific capacitances (highest specific capacitance for tin-based materials) of 1204F g^-1 and 764F g^-1 for two samples at a current density of 1 A g^-1 in 6 M KOH can respectively be achieved, and their capacitance retention remained at 95.1% and 89.2% even after 15,000 cycles at a current density of 10 A g^-1. Furthermore, a flexible quasi-solid-state asymmetric supercapacitor composed of Sn(OH)₂(PPh₃)₂ and activated carbon was assembled and exhibited a specific capacitance of 290.6 mF cm^-2 at a current density of 1 mA cm^-2. More importantly, this device also displayed excellent cyclic stability of ∼100% for 1800 cycles during the galvanostatic charge/discharge process at 5 mF cm^-2.

Oxygen-Deficient Stannic Oxide/Graphene for Ultrahigh-Performance Supercapacitors and Gas Sensors

The metal oxides/graphene nanocomposites have great application prospects in the fields of electrochemical energy storage and gas sensing detection. However, rational synthesis of such materials with good conductivity and electrochemical activity is the topical challenge for high-performance devices. Here, SnO₂/graphene nanocomposite is taken as a typical example and develops a universal synthesis method that overcome these challenges and prepares the oxygen-deficient SnO₂ hollow nanospheres/graphene (r-SnO₂/GN) nanocomposite with excellent performance for supercapacitors and gas sensors. The electrode r-SnO₂/GN exhibits specific capacitance of 947.4 F g⁻¹ at a current density of 2 mA cm⁻² and of 640.0 F g⁻¹ even at 20 mA cm⁻², showing remarkable rate capability. For gas-sensing application, the sensor r-SnO₂/GN showed good sensitivity (~13.8 under 500 ppm) and short response/recovering time toward methane gas. These performance features make r-SnO₂/GN nanocomposite a promising candidate for high-performance energy storage devices and gas sensors.