Facile synthesis of α-MnO₂ nanorod/graphene nanocomposite paper electrodes using a 3D precursor for supercapacitors and sensing platform to detect 4-nitrophenol

Manganese dioxide (α-MnO₂)/reduced graphene oxide (RGO) nanocomposite paper was synthesized using a 3D precursor manganese benzoate dihydrazinate for supercapacitor and sensor applications. The new 3D precursor and residue-free synthesis are the advantages of this method. Transmission electron microscopy showed that MnO₂ nanorods with a mean diameter of <10 nm were decorated densely over the RGO surface. Owing to the paper's freestanding structure, the composite was used directly as a binder-free electrode in the electrochemical experiments. The composite exhibited a higher capacitance of 360 F g⁻¹ at a current density of 2.5 A g⁻¹ as well as a long cycle life with 7.0% capacitance loss after 10,000 cycles. The specific capacitance reached 228 F g⁻¹ at a current density of 25 A g⁻¹. In addition, the developed electrochemical sensor showed a linear relationship with the 4-nitrophenol (4-NP) concentration from 1 to 100 μM with a detection limit of 0.017 μM. The sensor was used to determine the level of 4-NP in tap water and river water samples with good recovery, highlighting the sensor's feasibility for industrial applications. Overall, this composite paper is a promising electrode material for flexible supercapacitors and sensors.