A capacitive intermetallic MnN was synthesized via nitridation ofMnO(2) at 800. C under NH3 atmosphere. A volumetric capacitance of 1044.3 F cm(-3) was found in 1 mol dm(-3) Na2SO4 (aq) using a current density of 1 A g(-1), and less than 1% of capacitance was lost after 5000 ladder cycles. 89.3% of the initial volumetric capacitance remained at a current density of 10 A g(-1). A reversible electrode process controlled by diffusion and a high electrical conductivity during charging-discharging ensured a long cycle life. The assembled symmetrical capacitor of MnN/Na2SO4 (aq)/MnN shows a high volumetric energy density of 112.2 W h L-1, facilitating heavy-duty applications. (C) 2016 The Electrochemical Society.