Improving the Supercapacitance Performance of V 2 O 5 Interconnected Al 2 O 3 Composite Electrode for Energy Storage Application

Cellulose nanofiber (CNF) and hybrid zeolite imidazole framework (HZ) are an emerging biomaterial and a porous carbonous material, respectively. The composite of these two materials could have versatile physiochemical characteristics. A cellulose nanofiber and cobalt-containing zeolite framework-based composite was prepared using an in-situ and eco-friendly chemical method followed by pyrolysis. The composite was comprised of cobalt nanoparticles decorated on highly graphitized N-doped nanoporous carbons (NPC) wrapped with carbon nanotubes (CNTs) produced from the direct carbonization of HZ. By varying the ratio of CNF in the composite, we determined the optimal concentration and characterized the derived samples using sophisticated techniques. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of CNF in the metallic cobalt-covered N-doped NPC wrapped with CNTs. The CNF–HZNPC composite electrodes show superior electrochemical performance, which is suitable for supercapacitor applications; its specific capacitance is 146 F/g at 1 A/g. Furthermore, the composite electrodes retain a cycling stability of about 90% over 2000 charge–discharge cycles at 10 A/g. The superior electrochemical properties of the cellulose make it a promising candidate for developing electrodes for energy storage applications.

Hydrothermal synthesis of Polypyrrole/MoS2 intercalation composites for supercapacitor electrodes

Metal oxide materials can display unique electronic, structural, and optical properties when scaled down to nanometer dimensions and find utility in many applications such as ferroelectrics and piezoelectrics, superconductors, dielectrics, heterogeneous catalysis, photocatalysis, fuel cells, and batteries. To this end, the ability to fabricate or synthesize functional oxides in a variety of nanostructured geometries is important. In this presentation, three example systems will be presented detailing new synthetic approaches to obtaining metal oxides with advanced nanostructured morphologies. The effect of the nanostructured morphology on the structure and properties of the materials will also be discussed. Recently, there has been much interest in developing synthesis methods to obtain nanostructures with higher order geometries such as branching or hyperbranching. The ability to synthesize metal oxides in hierarchical structures can allow for new properties or phenomena not observable in bulk morphologies. In the first example, the solution-phase synthesis of cubic perovskite potassium lanthanum titanate into orthogonal nanostructures with hyperbranched and hexapod morphology will be discussed. A facile hydrothermal reaction without using a template, catalyst, substrate, or structure-directing agent was employed. The properties of the hyperbranched materials as water splitting photocatalysts for hydrogen generation will be discussed. In the second example, our efforts towards understanding the materials chemistry of nanostructured solid state Li-ion conductors, which are attractive as safer alternatives to liquid organic electrolytes, will be presented. Our group has developed electrospinning methods for synthesizing titanate and zirconate-based Li-ion conducting ceramics into nanowire morphologies. Some of the improved properties we have observed in these solid electrolyte nanowires, such as improved sintering characteristics, phase stability, and Li ionic conductivity, will be discussed. Finally, our efforts towards the synthesis of functional 2D nanosheets comprising Li-ion battery cathode materials such as LiCoO2 and LiNi1/3Mn1/3Co1/3O2 will be presented. 2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials. The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials comprised of layers of different cathode materials may be possible by reassembling different nanosheets. However, the synthesis of Li-rich materials into 2D nanosheets is challenging due to the strong interlayer electrostatic interactions and binding by protons during osmotic swelling processes, which can block Li sites. Our modified osmotic swelling approach circumvents these problems and allows for the synthesis of 2D nanosheets from Li-rich materials that can be restacked and display the expected electrochemical properties of bulk counterparts. Our work is a firm step forward for improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.

Improving the electrochemical performance of biomass-derived carbon electrode-active materials for supercapacitor applications has recently attracted considerable attention. Herein, we develop hybrid electrode materials from rice-husk-derived porous carbon (RH-C) materials and β-Ni(OH)2 via a facile solid-state reaction strategy comprising two steps. The prepared RH-C/Ni(OH)2 (C–Ni) was investigated using scanning electron microscopy (SEM) (energy-dispersive X-ray spectrometer (EDS)), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) to acquire the physical and chemical information, which was used to demonstrate the successful fabrication of C–Ni. Thermogravimetric analysis (TGA) measurement results confirmed that the thermal stability of C–Ni changed due to the presence of Ni(OH)2. As expected, C–Ni possesses a high capacitance of ∼952 F/g at a current density of 1.0 A/g. This result is higher than that of pure biomass-based carbon materials under the three-electrode system. This facile preparation method, which was used to synthesize the electrode-active materials, can extend to the value-added utility of other waste biomass materials as high-performing supercapacitor electrodes for energy storage applications.

A high demand of energy storage devices has boosted researchers for fabricating ultra-efficient supercapacitors with better energy density and cycling stability. CeO2 nanofibers are one of the most promising materials due their superior oxidation performance as well as a larger specific capacitance that enables them to hold more charge. However, metal oxides being poor electrical conductors hinder the performance of the device. In this present work, we adopted a novel approach to improve the conductivity of the electrodes and charge storing capability of the device by making a hybrid composite structure with conducting porous carbon and long chain polymers through a simple, efficient and low temperature based hydrothermal synthesis route. This approach boosts the charge storage capability of the electrode electrochemically as well as by the pseudo-capacitive effect from CeO2 nanofibers. The structure and morphology of CeO2 nanofibers were characterized by field emission scanning electron microscopy (FESEM). FESEM confirmed highly dense CeO2 nanofibers that were less than 30 nm in diameter. Electrochemical measurement of CeO2 nanofibers hybrid composite shows improved specific capacitance value with very large cycling stability.

Nanostructured cobalt oxide and cobalt sulfide for flexible, high performance and durable supercapacitors

2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Lithium-ion batteries and supercapacitors are widely used to power mobile devices, but the energy and power densities of the electrode materials still need improvement. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials. The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials composed layers of different cathode materials may be possible by reassembling different nanosheets. These sandwich structures could potentially result in unique synergistic effects and novel redox behavior due to the interactions from different sheets. Finally, we can obtain better understanding of the structure of complex layered cathode materials through exfoliation and high resolution ex-situ microscopy studies. Here we present our synthesis of 2D nanosheets of two common lithium-ion battery materials, LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC). Nanosheets were obtained by exfoliation of LCO and NMC particles using traditional osmotic swelling with tetraethylammonium (TEA). TEM, SEM and AFM analysis showed that the particles were successfully exfoliated nanosheets with around 2 nm thickness. XRD and SADP[CKC1] analysis showed that these materials had hexagonal structures with good crystallization. A reassembly process was developed and applied to obtain LCO, NMC, and LCO/NMC hybrid particles. Electrochemical evaluation of the particles as electrodes for lithium-ion batteries and supercapacitors were performed. Our work is a firm step forward on improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.

Cube Fe3O4 nanoparticles embedded in three-dimensional net porous carbon from silicon oxycarbide for high performance supercapacitor

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1−xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9 F g−1 at 1 A g−1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10 A g−1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.

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.

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO ₂ Reduction

Synthesis and Characterization of LiFeBO3/C Composite By Spray Pyrolysis with Heat Treatment

Material design based on impurity element doping for photoelectrochemical capacitor composite electrodes using metal oxides

Photocatalytic conversion of biomass is considered an effective, clean, and environmentally friendly route to obtain high-valued chemicals and hydrogen. However, the limited conversion efficiency and poor selectivity are still the main bottlenecks for photocatalytic biomass conversion. Herein, we report the highly selective photocatalytic conversion of glucose solution on holo-symmetrically spherical three-dimensionally ordered macroporous TiO₂-CdSe heterojunction photonic crystal structure (s-TCS). The obtained s-TCS photocatalysts show excellent stability and strong light harvesting, uniform mass diffusion and exchange, and efficient photogenerated electrons/holes separation and utilization. The optimized s-TCS-4 photocatalyst displays the highest photocatalytic performance for glucose oxidation and hydrogen production. The glucose conversion, lactic acid selectivity, and yield on s-TCS-4 are about 95.9%, 94.3%, and 96.4%, respectively. The photocatalytic production of lactic acid for s-TCS-4 (18.5 g/L) is 2.3 times higher than the pure spherical TiO₂ photonic crystal without CdSe (s-TiO₂, 8.1 g/L), and the hydrogen production rate of s-TCS-4 is 9.4 times that of s-TiO₂. For the first time, we reveal that the photocatalytic conversion of glucose to lactic acid is a third-order and four-electron-involved reaction. This work could shed some new light on the efficient photocatalysis conversion of biomass to highly value-added products with high selectivity and yield, and simultaneously sustainable hydrogen evolution.

The different effect of Co3O4 or/and carbon fiber originated from biomass on the electrochemical hydrogen storage performance of Co2B alloy