As a novel kind of carbon-based material, carbon aerogels have attracted widespread attention owing to their integrated properties of a large internal surface area, small pore size, and outstanding mechanical strength. In this study, a fascinating carbon aerogel has been rationally designed with a unique cellular structure, consisting of one-dimensional carbon nanofibers derived from oxidized polyacrylonitrile (o-PAN) and two-dimensional carbon sheets originating from polyimide (PI). The interconnected o-PAN/PI (oPP) carbon aerogel exhibits low density but increased mechanical strength and can not only act as a versatile adsorbent but also as an ideal template for the in situ growth of MnO2 nanosheets to obtain oPP@MnO2 hybrid carbon aerogel. The oPP@MnO2 composite aerogel exhibits extraordinary electrochemical characteristics with a maximum specific capacitance of 1066 F g(-1), approaching the theoretical value (1370 F g(-1)) of MnO2. Moreover, an assembled oPP@MnO2//activated oPP (A-oPP) asymmetric supercapacitor delivers a considerably high energy density of up to 30.3 W h k g(-1), highlighting the advantages of the unique cellular structure of the oPP carbon aerogel and oPP@MnO2 hybrid carbon aerogel. Therefore, the successful fabrication of the oPP carbon aerogel widens the scope of traditional electrospun lamellar membranes to multi-dimensional aerogels, providing a new strategy for the construction of nanofiber-based materials for energy storage and environmental protection applications.