Porous Mo-C coverage on ZnO rods for enhanced supercapacitive performance.

ZnO is a promising electrode material with advantages such as high environmental benignity, low cost and easy synthesis. Like other non-carbon electrode materials, ZnO has low resistivity and is therefore often combined with carbon materials to obtain favorable electronic conductivity. Herein, ZnO rods were prepared and coated with a carbon layer (Mo-C) as a supercapacitive electrode material for supercapacitors. Particularly, the porosity of the carbon layer is increased by modification with MoO42- which serves as chelating agent during the carbonation of dopamine hydrochloride. Compared to dense carbon coating layers, the porous carbon coverage is more favorable for electrolyte accessibility, thereby simultaneously promoting electronic and ionic transmission to ZnO. With these favorable features, the resultant ZnO@Mo-C composite displayed outstanding capacitances (900 F g-1 at 1 A g-1) and high rate capability (650 F g-1 at 10 A g-1). In addition, an asymmetric supercapacitor device was constructed using ZnO@Mo-C and activated carbon as the positive and negative electrodes, respectively, which realized an enlarged voltage profile of 0-1.5 V, stable cyclability with a capacitance retention of 97% and acceptable power/energy densities. Moreover, the method to produce the ZnO@Mo-C rods is facile and environmentally friendly and can be readily extended to other carbon coated materials.