Manganese dioxide (alpha-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 mu M with a detection limit of 0.017 M. 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. (C) 2016 Elsevier Ltd. All rights reserved.