Topochemical Transformation of Two-Dimensional VSe 2 into Metallic Nonlayered VO 2 for Water Splitting Reactions in Acidic and Alkaline Media.

The engineering of the structural and morphological properties of nanomaterials is a fundamental aspect to attain desired performance in energy storage/conversion systems and multifunctional composites. We report the synthesis of room temperature-stable metallic rutile VO 2 (VO 2 (R)) nanosheets by topochemically transforming liquid-phase exfoliated VSe 2 in a reductive Ar-H 2 atmosphere. The as-produced VO 2 (R) represents an example of two-dimensional (2D) nonlayered materials, whose bulk counterparts do not have a layered structure composed by layers held together by van der Waals force or electrostatic forces between charged layers and counterbalancing ions amid them. By pretreating the VSe 2 nanosheets by O 2 plasma, the resulting 2D VO 2 (R) nanosheets exhibit a porous morphology that increases the material specific surface area while introducing defective sites. The as-synthesized porous (holey)-VO 2 (R) nanosheets are investigated as metallic catalysts for the water splitting reactions in both acidic and alkaline media, reaching a maximum mass activity of 972.3 A g -1 at -0.300 V vs RHE for the hydrogen evolution reaction (HER) in 0.5 M H 2 SO 4 (faradaic efficiency = 100%, overpotential for the HER at 10 mA cm -2 = 0.184 V) and a mass activity (calculated for a non 100% faradaic efficiency) of 745.9 A g -1 at +1.580 V vs RHE for the oxygen evolution reaction (OER) in 1 M KOH (overpotential for the OER at 10 mA cm -2 = 0.209 V). By demonstrating proof-of-concept electrolyzers, our results show the possibility to synthesize special material phases through topochemical conversion of 2D materials for advanced energy-related applications.