<p>X-ray powder diffraction analysis, scanning electron microscopy, Emmet–Teller method, and electrochemical impedance spectroscopy were used to investigate morphology impact on non-Faradaic capacity in the three types of manganese dioxides phases. Pore radii distributions were obtained from isotherms in terms of the density functional theory. The XRD patterns detected the changes in the ratio of various manganese dioxide phases (Mn₂O₃, mixture of Mn₂O₃ and Mn₃O₄, and Mn₃O₄) with a rising concentration of citric acid under melting treatment of Mn₂O₃ in solid citric acid media. The changes in manganese dioxide phases impact nanoscopic network, size of crystallites, pore sizes, and surface area of the samples. Experimental results demonstrate a correlation between micropore volume, surface area, average pore radius, crystallite size, and non-Faradaic capacitance of various manganese dioxides. Mn₃O₄ with oxygen deficit has maximum non-Faradaic capacitance, average micropore volume, surface area, and crystallite size.</p> Graphical abstract <p></p>