Two-Dimensional NH 4 V 3 O 8 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) NH 4 V 3 O 8 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-NH 4 V 3 O 8 flakes show an acceptable hydrogen evolution performance in 0.5 M H 2 SO 4 on a glassy carbon electrode (GCE) coated with 2D-NH 4 V 3 O 8 , 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-NH 4 V 3 O 8 nanoflakes were found to be ideal for supercapacitor electrodes. The NH 4 V 3 O 8 working electrode in 1 M Na 2 SO 4 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-NH 4 V 3 O 8 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 NH 4 V 3 O 8 material provide a promising candidate for not only energy conversion but also energy-storage applications.