In situ fabrication of MoO2–Ni3(PO4)2/NF heterojunction composite material for application as a supercapacitor electrode†

Supercapacitors, as highly regarded energy storage devices, have garnered vital attention in recent years. Developing electrode materials exhibiting great electrochemical performance is at the core of supercapacitor research. Constructing heterojunction structures can improve the electrochemical performance of electrode materials effectively. Heterojunction structures can mutually compensate for their limitations, facilitating electron transfer and reactions. Herein, a MoO₂–Ni₃(PO₄)₂/NF (NF = nickel foam) heterojunction was in situ synthesized on NF via a two-step method combining hydrothermal synthesis and chemical vapor deposition (CVD), using polyoxometalate (NH₄)₆[NiMo₉O₃₂]·6H₂O as the precursor. This heterojunction provides more active sites and enhances conductivity. The MoO₂–Ni₃(PO₄)₂/NF heterojunction exhibits a galvanostatic charge–discharge (GCD) time of up to 643 s at a current density of 1 A g⁻¹. It displays a specific capacitance of 396 F g⁻¹ and retains 82.2% after 1000 cycles. The asymmetric supercapacitor (ASC) device with this modified electrode material has 50% capacitance retention after 1000 cycles of charge and discharge. The specific capacitance of the ASC device at 1 A g⁻¹ current density is 30.5 F g⁻¹, presenting an energy density of 3.8 W h kg⁻¹, and a power density of 0.13 W kg⁻¹. Therefore, the MoO₂–Ni₃(PO₄)₂/NF heterojunction, as an electrode material for supercapacitors, demonstrates excellent application potential.