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

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.