Nitrogen-Incorporated Reduced Graphene Oxides as Electrode Materials for Tunable Electrochemical Applications

Abstract

Because of high defect density and good electrical conductance, nitrogen-incorporated reduced graphene oxides (NrGOs) are highly promising materials for energy storage, energy conversion, and electrochemical applications. Surface area modifications and controllable electrical conductivity coupled with micromesopore structures make these materials suitable for ion adsorption and transport for tunable electrochemical performance as metal-free electrocatalysts, supercapacitor electrodes, electrochemical sensors, and anode materials in batteries. However, a systematic investigation into the structural evolution and alteration of electronic properties of NrGO with varying degrees of nitrogen incorporation is required to better understand the electrochemical benefits of these materials. To this aim, a series of NrGO samples were prepared from graphene oxide (GO) via a solvothermal route, with melamine playing the combined role of nitrogen precursor and reducing agent. Here, we have obtained NrGO with the highest N/C atomic percentage of 8.1% for the maximum melamine-to-GO precursor ratio (2:1) used. Alongside improved reduction, Raman spectroscopy probes increased disorder in the NrGO matrix with nitrogen incorporation, in accordance with a diminishing sp2 fraction and an average separation between defects. A drop in bulk conductivity, specific capacitance, and electrochemically active surface area (ECSA) values from reduced graphene oxide (rGO) is observed for the NrGO prepared with the lowest melamine ratio, with a gradual improvement in all of the above properties being evident with increasing nitrogen incorporation in the NrGO matrix. Controlled electrochemical activity of NrGO samples correlates with the combined effects of bulk conductivity, pore volume, and growing disorder in the rGO matrix, rather than N incorporation alone. These results provide valuable insights into the challenges associated with NrGO when used as an electrode material for electrochemical applications.