Two-Dimensional NHVO 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) NHVO 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-NHVO flakes show an acceptable hydrogen evolution performance in 0.5 M HSO on a glassy carbon electrode (GCE) coated with 2D-NHVO, which results in a low overpotential of 314 mV at -10 mA cm with an excellent Tafel slope as low as 90 mV dec. So far, with the main focus on energy storage, 2D-NHVO nanoflakes were found to be ideal for supercapacitor electrodes. The NHVO working electrode in 1 M NaSO shows an excellent electrochemical capability of 274 F g at 0.5 A g for a maximum energy density of 38 W h kg at a power density as high as 250 W kg. Moreover, the crystal structure of 2D-NHVO is demonstrated by density functional theory (DFT) computational simulation using three functionals, GGA, GGA + , and HSE06. The simple preparation, low cost, and abundance of the NHVO material provide a promising candidate for not only energy conversion but also energy-storage applications.