Comparing the Performance of Nb 2 O 5 Composites with Reduced Graphene Oxide and Amorphous Carbon in Li‐ and Na‐Ion Electrochemical Storage Devices

Morphology and Crystallinity Effects of Nanochanneled Niobium Oxide Electrodes for Na-Ion Batteries

Niobium pentoxide (Nb2O5) is a promising negative electrode for sodium ion batteries (SIBs). By engineering the morphology and crystallinity of nanochanneled niobium oxides (NCNOs), the kinetic behavior and charge storage mechanism of Nb2O5 electrodes were investigated. Amorphous and crystalline NCNO samples were made by modulating anodization conditions (20-40 V and 140-180 °C) to synthesize nanostructures of varying pore sizes and wall thicknesses with identical chemical composition. The electrochemical energy storage properties of the NCNOs were studied, with the amorphous samples showing better overall rate performance than the crystalline samples. The enhanced rate performance of the amorphous samples is attributed to the higher capacitive contributions and Na-ion diffusivity analyzed from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT). It was found that the amorphous samples with smaller wall thicknesses facilitated improved kinetics. Among samples with similar pore size and wall thickness, the difference in their power performance stems from the crystallinity effect, which plays a more significant role in the resulting kinetics of the materials for Na-ion batteries.

Layered Potassium Titanium Niobate/Reduced Graphene Oxide Nanocomposite as a Potassium-Ion Battery Anode

With graphite currently leading as the most viable anode for potassium-ion batteries (KIBs), other materials have been left relatively under-examined. Transition metal oxides are among these, with many positive attributes such as synthetic maturity, long-term cycling stability and fast redox kinetics. Therefore, to address this research deficiency we report herein a layered potassium titanium niobate KTiNbO5 (KTNO) and its rGO nanocomposite (KTNO/rGO) synthesised via solvothermal methods as a high-performance anode for KIBs. Through effective distribution across the electrically conductive rGO, the electrochemical performance of the KTNO nanoparticles was enhanced. The potassium storage performance of the KTNO/rGO was demonstrated by its first charge capacity of 128.1 mAh g-1 and reversible capacity of 97.5 mAh g-1 after 500 cycles at 20 mA g-1, retaining 76.1% of the initial capacity, with an exceptional rate performance of 54.2 mAh g-1 at 1 A g-1. Furthermore, to investigate the attributes of KTNO in-situ XRD was performed, indicating a low-strain material. Ex-situ X-ray photoelectron spectra further investigated the mechanism of charge storage, with the titanium showing greater redox reversibility than the niobium. This work suggests this low-strain nature is a highly advantageous property and well worth regarding KTNO as a promising anode for future high-performance KIBs.

In-situ formation of niobium oxide – niobium carbide – reduced graphene oxide ternary nanocomposite as an electrochemical sensor for sensitive detection of anticancer drug methotrexate

Engineering the nanostructure of an electrocatalyst is crucial in developing a high-performance electrochemical sensor. This work exhibits the hydrothermal followed by annealing synthesis of niobium oxide/niobium carbide/reduced graphene oxide (NbO/NbC/rGO) ternary nanocomposite. The oval-shaped NbO/NbC nanoparticles cover the surface of rGO evenly, and the rGO nanosheets are interlinked to produce a micro-flower-like architecture. The NbO/NbC/rGO nanocomposite-modified electrode is presented here for the first time for the rapid and sensitive electrochemical detection of the anticancer drug methotrexate (MTX). Down-sized NbO/NbC nanoparticles and rGO's high surface area provide many active sites with a rapid electron transfer rate, making them ideal for MTX detection. In comparison to previously reported MTX sensors, the developed drug sensor exhibits a lower oxidation potential and a higher peak current responsiveness. The constructed sensors worked analytically well under optimal conditions, as shown by a low detection limit of 1.6 nM, a broad linear range of 0.1-850 µM, and significant recovery findings (∼98 %, (n = 3)) in real samples analysis. Thus, NbO/NbC/rGO nanocomposite material for high-performance electrochemical applications seems promising.

Heterostructured and Mesoporous Nb2O5@TiO2 Core-Shell Spheres as the Negative Electrode in Li-Ion Batteries

Niobium pentoxides have received considerable attention and are promising anode materials for lithium-ion batteries (LIBs), due to their fast Li storage kinetics and high capacity. However, their cycling stability and rate performance are still limited owing to their intrinsic insulating properties and structural degradation during charging and discharging. Herein, a series of mesoporous Nb₂O₅@TiO₂ core-shell spherical heterostructures have been prepared for the first time by a sol-gel method and investigated as anode materials in LIBs. Mesoporosity can provide numerous open and short pathways for Li⁺ diffusion; meanwhile, heterostructures can simultaneously enhance the electronic conductivity and thus improve the rate capability. The TiO₂ coating layer shows robust crystalline skeletons during repeated lithium insertion and extraction processes, retaining high structural integrity and, thereby, enhancing cycling stability. The electrochemical behavior is strongly dependent on the thickness of the TiO₂ layer. After optimization, a mesoporous Nb₂O₅@TiO₂ core-shell structure with a ∼13 nm thick TiO₂ layer delivers a high specific capacity of 136 mA h g^-1 at 5 A g^-1 and exceptional cycling stability (88.3% retention over 1000 cycles at 0.5 A g^-1). This work provides a facile strategy to obtain mesoporous Nb₂O₅@TiO₂ core-shell spherical structures and underlines the importance of structural engineering for improving the performance of battery materials.

Colorimetric biosensor for visual determination of Golgi protein 73 based on reduced graphene oxide-carboxymethyl chitosan-Hemin/platinum@palladium nanozyme with peroxidase-like activity

A Golgi protein 73 (GP73) colorimetric biosensor based on the reduced graphene oxide-carboxymethyl chitosan-hemin/platinum@palladium nanoparticles (RGO-CMCS-Hemin/Pt@Pd NPs) with peroxidase-like activity was constructed. The RGO-CMCS-Hemin/Pt@Pd NPs with high peroxidase-like activity were successfully synthesized under mild conditions. Then, the aminylated GP73 aptamer (Apt) was bound to the RGO-CMCS-Hemin/Pt@Pd NPs to form the recognition probe. Another unmodified GP73 aptamer (AptI) was served as the capture probe. In the presence of target GP73, the capture probe and the recognition probe specifically bind to GP73 and form a RGO-CMCS-Hemin/Pt@Pd NP-Apt/GP73/AptI sandwich-type structure, which can oxidase the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB in the presence of H₂O₂. GP73 detection was achieved by measuring the peak UV absorption at 652 nm. Under the optimum conditions, the GP73 concentration was linearly related to the absorbance intensity in the range 10.0-110.0 ng/mL, and the limit of detection (LOD) was 4.7 ng/mL. The proposed colorimetric biosensor was successfully applied to detect GP73 in spiked human serum samples with recoveries of 98.2-107.0% and RSDs of 1.90-5.44%, demonstrating the excellent potential for highly sensitive GP73 detection in clinical detection. A colorimetric biosensor for visual determination of GP73 based on RGO-CMCS-Hemin/Pt@Pd NPs nanozyme with peroxidase-like activity was designed. The GP73 biosensor responses linearly from 10.0-110.0 ng/mL with LOD of 4.7 ng/mL, and shows acceptable specificity and good recovery.

Design of Binary Nb2O5-SiO2 Self-Standing Monoliths Bearing Hierarchical Porosity and Their Efficient Friedel-Crafts Alkylation/Acylation Catalytic Properties

Alkylation of aromatic hydrocarbons is among the most industrially important reactions, employing acid catalysts such as AlCl₃, H₂SO₄, HF, or H₃PO₄. However, these catalysts present severe drawbacks, such as low selectivity and high corrosiveness. Taking advantage of the intrinsic high acid strength and Lewis and Brønsted acidity of niobium oxide, we have designed the first series of Nb₂O₅-SiO₂(HIPE) monolithic catalysts bearing multiscale porosity through the integration of a sol-gel process and the physical chemistry of complex fluids. The MUB-105 series offers efficient solvent-free heterogeneous catalysis toward Friedel-Crafts monoalkylation and -acylation reactions, where 100% conversion has been reached at 140 °C while cycling. Alkylation reactions employing the MUB-105(1) catalyst have a maximum turnover number (TON) of 104 and a turnover frequency (TOF) of 9 h^-1, whereas for acylation, MUB-105(1) and MUB-105(2) yield maximum TON and TOF values of 107 and 11 h^-1, respectively. Moreover, the catalysts are selective, producing equal amounts of ortho- and para-substituted alkylated products and greater than 90% of the para-substituted acylated product. The highest catalytic efficiencies are obtained for the MUB-105(1) catalyst, bearing the smallest Nb₂O₅ particle sizes, lowest Nb₂O₅ content, and the highest amorphous character. The catalysts presented here are in a monolithic self-standing state, offering easy handling, reusability, and separation from the final products.

Pomegranate-like structured Nb2O5/Carbon@N-doped carbon composites as ultrastable anode for advanced sodium/potassium-ion batteries

The distinctive pomegranate-like Nb₂O₅/Carbon@N-doped carbon (Nb₂O₅/C@NC) composites are fabricated using hydrothermal method integrated with nitrogen doped carbon coating procedure. For the SIBs anode, the Nb₂O₅/C@NC composites present superior rate character and sustainable capacity (117 mAh g^-1 upon 1000 cycles at 5 A g^-1). The in-situ X-ray diffraction (XRD) is utilized to research its sodium storage mechanism. Furthermore, for PIBs, the Nb₂O₅/C@NC composites present sustainable capacity (81 mAh g^-1 upon 1000 cycles at 1 A g^-1). The outstanding performance of Nb₂O₅/C@NC composites is ascribed to its unique architecture, in which Nb₂O₅ nanocrystals embedded in porous carbon can restrain agglomeration of Nb₂O₅ nanocrystals, enhance electron/ion diffusion kinetics, and ensure electrolyte accessibility, and moreover, NC shell layer can provide effective active sites and further increase ions/electrons transfer.

Thin niobium and iron–graphene oxide composite metal–organic framework electrodes for high performance supercapacitors

A new composite NbOF–GO and FeOF–GO electrode material was synthesized by the screw-capped pressure tube method for a supercapacitor with specific capacitance values of 599 and 459 F g⁻¹ at current densities of 0.5 and 0.2 A g⁻¹.