Interface-engineered VOPO4.2H2O/V2O5 binary heterostructure for high-performance supercapacitor applications

The escalating demand for high-performance energy storage has driven the development of advanced electrode materials for supercapacitors. Hydrated vanadium oxyphosphate (VOPO 4 .2H 2 O) is a promising electrode candidate owing to its layered structure, high theoretical capacitance, and variable vanadium valence states; however, low intrinsic electronic conductivity and sluggish reaction kinetics restrict its high-rate performance. This scientific research reports the hydrothermal synthesis of a VOPO 4 .2H 2 O/V 2 O 5 binary composite (~ 81 wt% VOPO 4 .2H 2 O / ~19 wt% V 2 O 5 ) in which two-dimensional VOPO 4 .2H 2 O nanosheets serve as a structural scaffold for V 2 O 5 nanoparticles, creating a synergistic P-O-V heterointerface. Comprehensive characterisation by XRD, FT-IR, Raman, FESEM, HRTEM, EDS mapping, and XPS confirmed successful binary composite formation. Scherrer analysis revealed ~ 25% crystallite size reduction relative to the pure phases, and XPS confirmed V 5+ as the dominant oxidation state with interfacial charge redistribution at the P-O-V boundary. In a three-electrode configuration (0.5 M K 2 SO 4 ), the composite delivered a specific capacitance of 248 F g − 1 at 1 A g − 1 , a near-unity b-value of 0.98, and a charge-transfer resistance of 1.2 Ω. Dunn’s kinetic analysis confirmed an intercalation pseudocapacitive mechanism, with the capacitive contribution increasing from 34.5% at 10 mV s − 1 to 70.2% at 200 mV s − 1 . An asymmetric coin-cell device (VOPO 4 .2H 2 O/V 2 O 5 // activated carbon) achieved a peak energy density of 10.42 Wh kg − 1 at 335 W kg − 1 , with 83% capacitance retention over 5000 cycles and ≥ 97% Coulombic efficiency. These results establish the P-O-V interfacial chemistry as an effective design principle for next-generation vanadium-based supercapacitors.