Vanadium Pentoxide with H2O, K+, and Na+ Spacer between Layered Nanostructures for High‐Performance Symmetric Electrochemical Capacitors

Abstract Vanadium oxide 2D layered nanostructures with the hydrous form of potassium (K + ) and sodium (Na + ) are synthesized via hydrothermal reaction between VOSO 4 · x H 2 O and different persulfate oxidants ((NH 4 ) 2 S 2 O 8 , K 2 S 2 O 8 , and Na 2 S 2 O 8 ). The physicochemical characterization suggests that the synthesized V 2 O 5 · 3H 2 O nanostructures possess layered morphology with considerable amount of water molecules accommodated between the interlayer spacing of nanostructures. Moreover, samples obtained using K 2 S 2 O 8 and Na 2 S 2 O 8 oxidants have K + (6.41%) and Na + (0.38%) ions intercalated on the 2D nanostructure along with the water molecules. Subsequently, the synthesized samples are heat‐treated at 400 °C for 3 h in the air and it is observed that the structural and morphological aspects are highly affected due to the removal of surface‐ and lattice‐bonded water molecules. The electrochemical properties of the samples are studied by assembling symmetric supercapacitor devices utilizing the bare and heat‐treated samples in 1 m Na 2 SO 4 electrolyte. The fabricated device with bare V 2 O 5 · 3H 2 O samples shows maximum specific capacitance (>60%) than that of heat‐treated V 2 O 5 samples, which represents the positive influence of water molecule on electrochemical behavior of V 2 O 5 . Moreover, the bare sample V 2 O 5 · 3H 2 O (using (NH 4 ) 2 S 2 O 8 ) symmetric supercapacitor exhibits an excellent cyclic stability with high capacitance retention of ≈97% after 25 000 cycles.