Hierarchical sandwich-like MnOx/Ni1-xMnxOy@nanoporous nickel/MnOx nano-architecture was fabricated by dealloying a Ni25Mn75 precursor in 1.0M (NH4)(2)SO4 solution followed by electrochemical oxidation in 1.0M KOH solution. The dealloying process would generate both uniform nanoporous structure (chemical dealloying) and nanoporous structure with big crack channels (electrochemical dealloying at high potentials) with similar ligament-pore size of less than 10 nm. The electrochemical oxidation process then generates Ni/Mn mixed oxides/hydroxides filled in the nanopores by oxidizing the highly active nanoscale NiMn alloy ligaments. At the same time, the dissolved Mn ions in the nanopores (produced during the dealloying process) will be oxidized to form Mn oxides/hydroxides nanosheets attached to the nanoporous Ni surface when they diffuse out of the nanopores. With the highly conductive NiMn ligament core and large amount of metal oxides/hydroxides formed both in the nanopores and on the out-surface, the sandwich-like nanocomposite exhibits a high areal capacitance (similar to 7 F cm(-2)) with excellent rate performance and cycling stability when used as a free-standing supercapacitor electrode. (C) 2015 Published by Elsevier Ltd.