Synthesis and Evaluation of Self–Supporting Graphitic Carbon Nitride/Carbon Nanotube (GCN/CNT) ORR/OER Electrodes in Aqueous and Non–Aqueous Media

To address the sluggish kinetics of oxygen reduction and evolution reactions, it is important to focus on developing active and robust electrode structures. Herein, a GCN/CNT composite was synthesized using a facile stepladder annealing method and evaluated as an electrode for aqueous and non–aqueous systems, wherein this combination provided storage sites for the reactants and products while facilitating electron transfer, as well as active centers for oxygen reactions, making this composite a bifunctional electrode. Different mass ratios of GCN/CNT were explored to determine their effect on the catalytic properties of the electrode. Among them, the electrode with the lowest GCN content (18GCN/CNT) showed the highest activity and stability towards ORR and OER (ΔE = 1.07 V) in alkaline media, presumably due to its considerable surface area, improved electron conductivity, and nitrogen content. When employed as a Li–O₂ battery cathode, GCN/CNT showed lower overpotentials and better cycling stability than CNT due to the presence of GCN active sites. It delivered a discharge specific capacity of 3796 mAh g_GCN/CNT⁻¹ at a current density of 100 mA g_cathode⁻¹ (0.1C) and 35 cycles at a limited capacity of 1000 mAh g_GCN/CNT⁻¹. Moreover, the reversible formation and decomposition of the Li₂O₂ product after cycling was confirmed in the SEM images and XRD patterns.