Metastable 2D amorphous Nb2O5 for aqueous supercapacitor energy storage

Pioneering the synthesis of metastable 2D amorphous Nb2O5 with high electron mobility and ion transport rates through structure-confined growth with hexamethylenetetramine (HMTA). The prepared electrode exhibits an unprecedented 200,000-cycle life and outstanding performance in aqueous asymmetric supercapacitor at 1.7V. [Display omitted] •Pioneering the synthesis of 2D Nb2O5 through structure confined growth.•Metastable 2D amorphous interface offers exceptional energy storage performance.•The electrode exhibits ultra-high stability for aqueous capacitive energy storage. Nb2O5 is a promising electrode material of energy storage due to its high specific capacity and phase transition resistance. However, the facile generation of niobic acid poses a challenge, hindering controlled growth and impeding improvements in electrical conductivity and structural stability, especially in realizing two-dimensional (2D) Nb2O5. Herein, we have discerned that the addition of hexamethylenetetramine (HMTA) in ethanol solvent facilitates the controlled and restricted growth of metastable 2D amorphous Nb2O5 (a-Nb2O5) within graphene domains. Nitrogen atoms within HMTA, rich in lone pair electrons, strongly interact with niobium ions, promoting 2D amorphous growth on graphene interface. This unique 2D amorphous interface offers high surface area, enhanced electron mobility, rapid ion transport, and superior structural stability compared to crystalline counterparts. The prepared metastable 2D a-Nb2O5/rGO electrode exhibits unprecedented cycle life in aqueous asymmetric supercapacitor. This confined growth strategy offers a novel approach for the innovative design of metastable 2D materials.