Ion diffusion rate and contact surface area of conducting polymers increased by composite formation with nanometric-size materials make them promising materials in the fabrication of energy storage devices. In this work, electronically conducting polyaniline and manganese oxide (PANI/MnO 2 ) nanofibrous composites were electrochemically co-deposited on stainless steel from binder-free electrolyte solution. Structural characterization and morphological characterization of the materials were performed with Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). SEM images show fibrous micro/nano-architecture of the composites with cluster networking structure having 200-500 nm length and 100-200 nm diameter. Electrochemical and energy storage properties of the assynthesized materials were investigated with cyclic voltammetry (CV), galvanostatic charge discharge curves(GCDC), and potentiostatic electrochemical impedance spectroscopy (PEIS) without any binders. Electrochemical measurements as well as galvanostatic charge discharge curves at 1 mA constant current have shown maximum specific capacitance of 149 F/g for the composite prepared with 0.15 M MnSO 4 in the co-deposition bath. The composites retain 67% specific capacitance even after 400 cycles, indicating the stability of synthesized composite. PEIS confirms the pseudocapacitive nature of the synthesized composites. K E Y W O R D S conducting polymers, energy storage, impedance spectroscopy, PANI/MnO x composites How to cite this article: Shah A-u-HA, Khan MO, Bilal S, Rahman G, Hung HV. Electrochemical co-deposition and characterization of polyaniline and manganese oxide nanofibrous composites for energy storage properties.