Nanomaterials Embedded Nitrogen-Doped Graphene for Advanced Energy Storage and Conversion

Abstract

A facile synthesis of nitrogen-doped graphene with high atomic percentage of Nitrogen (9.2 at%) including high ratio of pyridinic N and graphitic N has been reported via thermal annealing of graphene oxide with uric acid. The resultant material shows efficient electrochemical properties for capacitances and bifunctional electrocatalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In spite of its remarkable electrochemical properties, the major limitation of the two-dimensional graphene like materials for device fabrication or commercial applications is the restacking nature of the layers. Designing a three-dimensional nanostructure via inserting metal nanoparticles or one-dimensional carbonaceous nanomaterials inside the graphene layers can prevent the restacking of the layers and hence enhance the electrochemical properties of the composites by providing higher electroactive surface area for electrolyte permeation, charge storage as well as active sites for electrocatalysis. To enhance the electrocatalytical activity of the synthesized nitrogen-doped graphene, a hybrid of nickel embedded nitrogen-doped graphene is developed. The composite shows superior noble-metal-free quadrafunctional electrocatalysis of oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and hydrogen peroxide oxidation reaction (HPOR) compared to commercial electrocatalysts of Pt/C and Ru/C. Alternatively, the insertion of carbon nanotubes inside the graphene layers and fabricating a lamellar three-dimensional nanostructure exhibit excellent supercapacitor behavior as fabricated as solid-state supercapacitor and high-rate capable anode for Li-ion battery as well as metal-free bifunctional electrocatalysis of ORR and OER. In addition, the decoration of copper nanoparticles in the three-dimensional nanostructured nitrogen-doped graphene/carbon nanotube composite further improves the conductivity and electrochemical properties via interconnecting network of copper nanoparticles and carbon nanotubes with the graphene layers and have been evaluated for high performance metal-ion battery applications. The resultant composites show promising electrochemical performances for developing as electrode materials for next generation energy storage and conversion devices like solid-state supercapacitor, metal-ion battery, metal-air battery and rechargeable fuel cells.