MnO2-Pd integrated into NbP2O7 electrodes for hybrid supercapacitors

Abstract

Achieving high energy storage in electrode materials necessitates an optimal balance among structural stability, electroactive site concentration, and electrical conductivity. The NbP2O7 though structurally stable it possesses limited electrochemical and electrical stability. The introduction of MnO2 and Pd to form a composite material helps to improve the capacity by providing a high density of redox-active sites attributed to Nb2+/Nb3+ and Mn2+/Mn3+/Mn4+ couples. The NbP2O7 was synthesized by hydrothermal route with subsequent electrodeposition of MnO2 onto NbP2O7 and inclusion of Pd to provide optimal interfacial contact and charge-transfer kinetics through electron hopping and diffusion through the composite material. This NbP@Mn electrode demonstrated a five-fold increase in areal capacity relative to pure NbP2O7. Additional performance improvements were realized by integrating palladium (Pd), which acts as an efficient conductive catalyst, promoting rapid charge transfer and further activating redox sites. The resulting NbP@Mn-Pd composite exhibited an areal capacity of 11.28 F/cm2 at a current density of 15 mA/cm2. To demonstrate practical application, an asymmetric supercapacitor was constructed with NbP@Mn-Pd as the positive electrode and activated carbon as the negative electrode in a Swagelok cell. This configuration delivered an energy density of 97 μWh/cm2 at a power density of 680 μW/cm2, along with remarkable cycling stability with 90% capacity retention over 40,000 cycles. These results reveal the synergistic benefits of Mn-assisted redox capabilities combined with Pd-facilitated conductivity, supporting the potential of NbP@Mn-Pd composites as advanced electrode candidates for high-performance energy storage applications. © 2026 Elsevier B.V.