Porous ZnCo2O4 nanostructures with hexamethylenetetramine (HMT) as adscititious alkali are fabricated via a facile hydrothermal route and heat treatment process. The morphology of the materials can be easily tuned from nanowires to nanobelts by simple varying the hydrothermal temperature. Due to the superiority of the porous nanostructure and the convenient ion transport, the obtained ZnCo2O4 nanostructures are further applied as electrode materials for supercapacitors and exhibit noticeable pseudocapacitive performance with high specific capacitance of 776.2 F g(-1) at 1 A g(-1) and good cycle stability (84.3% capacity retention at 3 A g(-1)). Moreover, a high-voltage asymmetric supercapacitor using the ZnCo2O4 as the anode assembled with the freeze-dried reduced graphene oxide (F-RGO) cathode displays superior electrochemical performance with an ultrahigh energy density (84.48 Wh kg(-1) at 0.4 kW kg(-1)), which reveals a great promise for practical application in electrochemical devices. (C) 2017 Elsevier Ltd. All rights reserved.