Synthesis of three-dimensional nitrogen/sulfur-co-doped graphene hydrogels at low temperature and atmospheric pressure for supercapacitor materials

Abstract

Heteroatom doping and three-dimensional (3D) porous structures are critical to the performance of graphene supercapacitor electrode materials. However, the conventional methods, such as chemical vapor deposition (CVD) and hydrothermal synthesis, require tedious processes and harsh conditions. In this work, we describe a very simple and efficient approach to fabricate a 3D nitrogen/sulfur-co-doped porous graphene hydrogel (3DNS-GH). It is found that thiourea can reduce graphene oxide (GO) obtaining 3DNS-GHs at low temperature and atmospheric pressure by adjusting the pH value, because the reducibility of thiourea significantly increases in acidic or alkaline media. Furthermore, the amount of nitrogen and sulfur doping and nano-pore structure varies with the pH value of solution. The 3DNS-GH exhibits uniform pore structure and can be directly used as electrode materials without additive binder. The binder-free electrode based on the optimum operating conditions (3DNS-GH-12) exhibit a high specific capacitance of 259.2 F g⁻¹ and retain 96.0% of its initial capacitance after 10,000 cycles in 2 M KOH solution at 10 A g⁻¹. Additionally, the symmetrical supercapacitor assembled by the 3DNS-GH-12 showed an impressive energy density of 6.08 W h kg⁻¹ and a high power density of 7.51 kW kg⁻¹. Therefore, these materials demonstrate excellent performance, indicating this route possess potential applied value in the production of supercapacitor electrode materials.