In this work, a metastable aqueous interface was fabricated for synthesizing mesoporous and high surface area MnO2. When urea was used as the additive, hierarchical spheres self-organized from ultrathin nano sheets were obtained. Its porous structure could be controlled through adjusting the urea concentration, and a maximum surface area of 407 m(2) g(-1) was achieved by this method, which is larger than the reported values. Due to the porous structure and high surface area, as-prepared MnO2 exhibited a specific capacitance of 775.4 F g(-1), at a current density of 0.1 A g(-1), and exhibited a 63.5% capacitance retention when the current density was increased from 0.1 A g 1 to 5 A g(-1). Durability studies showed a 63.7% capacitance retention after 2500 cycles. The metastable interfacial reaction approach could also be extended to other alloys with large surface area and porous structure, such as CoB alloy. This method provides a simple and low-cost method to synthesize high surface area and mesoporous materials. (C) 2017 Elsevier Inc. All rights reserved.