One-step solution combustion synthesis of cobalt-nickel oxides/C/Ni/CNTs nanocomposites as electrochemical capacitors electrode materials

With Co(NO3)(2).6H(2)O (oxidizer and Co source), Ni(NO3)(2).6H(2)O (oxidizer and Ni source) and citric acid (fuel) as starting materials, cobaltnickel oxides/C/Ni ternary nanocomposites have been synthesized by a scalable, one-step solution combustion process at only 300 degrees C within 30 min in air. In these composites, the metallic nickel and amorphous carbon (conductive phases) were in situ formed by the reduction of Ni2+ and carbonization of the excess citric acid during combustion, respectively. Experimental results indicated that the fuel:oxidant and Co:Ni molar ratios in precursor solution showed strong influences on the phase composition, morphology and electrochemical performance of products. With the increase of the fuel dosage, the products transformed from well-crystallized cubic NiO/Ni to Ni (nickel-related phases), then to relatively amorphous Ni/NiO and finally NiO. Electrochemical tests indicated that the optimized product showed a high specific capacitance of 446 F g(-1) at 1 A g(-1) (or 280 F g(-1) at 10 A g(-1)) with a Co:Ni:C6H8O7 molar ratio of 4:5:86/9. Significantly, besides its mild experimental conditions, the method could be used to prepare cobaltnickel oxides/C/Ni/CNTs quarternary nanocomposites by simply adding acid-treated CNTs into precursor combustion solution. Thanks to the high electrical conduction of CNTs, the specific capacitance could be further improved up to 579 F g(-1) at 1 A g(-1), or 350 F g(-1) at 10 A g(-1). (C) 2014 Elsevier B.V. All rights reserved.