Two-Dimensional NH4V3O8 Nanoflakes as Efficient Energy Conversion and Storage Materials for the Hydrogen Evolution Reaction and Supercapacitors

Herein, for the first time, we present two-dimensional (2D) NH₄V₃O₈ nanoflakes as an excellent material for both energy conversion of the hydrogen evolution reaction and storage of supercapacitors by a simple and fast two-step synthesis, which exhibit a completely sheet-like morphology, high crystallinity, good specific surface area, and also stability, as determined by thermogravimetric analysis. The 2D-NH₄V₃O₈ flakes show an acceptable hydrogen evolution performance in 0.5 M H₂SO₄ on a glassy carbon electrode (GCE) coated with 2D-NH₄V₃O₈, which results in a low overpotential of 314 mV at -10 mA cm^-2 with an excellent Tafel slope as low as 90 mV dec^-1. So far, with the main focus on energy storage, 2D-NH₄V₃O₈ nanoflakes were found to be ideal for supercapacitor electrodes. The NH₄V₃O₈ working electrode in 1 M Na₂SO₄ shows an excellent electrochemical capability of 274 F g^-1 at 0.5 A g^-1 for a maximum energy density of 38 W h kg^-1 at a power density as high as 250 W kg^-1. Moreover, the crystal structure of 2D-NH₄V₃O₈ is demonstrated by density functional theory (DFT) computational simulation using three functionals, GGA, GGA + U, and HSE06. The simple preparation, low cost, and abundance of the NH₄V₃O₈ material provide a promising candidate for not only energy conversion but also energy-storage applications.

A full flexible NH4+ ion battery based on the concentrated hydrogel electrolyte for enhanced performance

Nonmetal ammonium  NH 4 +  ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of NH 4 +  ion redox chemistry in flexible batteries, is still in its infancy. For the first time, we report a flexible full  NH 4 +  ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between NH4V3O8·2.9H2O nanobelts cathode and polyaniline (PANI) anode. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g-1  and capacity retention of 95% after 400 cycles at a specific current of 0.1 A g -1. The full flexible AIBs are then fabricated using hydrogel electrolytes with varied salt concentrations, to maximize the electrochemical performance. It is found that the battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance i.e., a capacity of 60 mAh g-1 while maintaining a capacity retention of 88% after 250 cycles at a specific current of 0.1 A g  -1. Moreover, the flexible AIB retains excellent electrochemical performance when bent at different angles, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for future developments of new electrochemical energy storage technology.

Electrochemical Investigation of Phenethylammonium Bismuth Iodide as Anode in Aqueous Zn2+ Electrolytes

Despite the high potential impact of aqueous battery systems, fundamental characteristics such as cost, safety, and stability make them less feasible for large-scale energy storage systems. One of the main barriers encountered in the commercialization of aqueous batteries is the development of large-scale electrodes with high reversibility, high rate capability, and extended cycle stability at low operational and maintenance costs. To overcome some of these issues, the current research work is focused on a new class of material based on phenethylammonium bismuth iodide on fluorine doped SnO₂-precoated glass substrate via aerosol-assisted chemical vapor deposition, a technology that is industrially competitive. The anode materials were electrochemically investigated in Zn²⁺ aqueous electrolytes as a proof of concept, which presented a specific capacity of 220 mAh g^-1 at 0.4 A g^-1 with excellent stability after 50 scans and capacity retention of almost 100%.

Tailoring the Size and Shape-New Path for Ammonium Metavanadate Synthesis

Ammonium metavanadate, NH₄VO₃, plays an important role in the preparation of vanadium oxides and other ammonium compounds, such as NH₄V₃O₈, (NH₄)₂V₃O₈, and NH₄V₄O₁₀, which were found to possess interesting electrochemical properties. In this work, a new route for the synthesis of NH₄VO₃ is proposed by mixing an organic ammonium salt and V₂O₅ in a suitable solvent. The one-step procedure is carried out at room temperature. Additionally, the need for pH control and use of oxidants necessary in known methods is eliminated. The mechanism of the NH₄VO₃ formation is explained. It is presented that it is possible to tailor the morphology and size of the obtained NH₄VO₃ crystals, depending on the combination of reagents. Nano- and microcrystals of NH₄VO₃ are obtained and used as precursors in the hydrothermal synthesis of higher ammonium vanadates. It is proven that the size of the precursor particles can significantly affect the physical and chemical properties of the resulting products.

Fabrication of V2O5 super long nanobelts: optical, in situ electrical and field emission properties

A low turn-on field of 1.4 V μm⁻¹, carrier concentrations of N_d = 1.48 × 10¹⁸ cm⁻³ and electron mobility of 1.26 cm² V⁻¹ s⁻¹ were obtained for V₂O₅ super long nanobelts.