Preparation and characterization of colorful graphene oxide papers and flexible N‐doping graphene papers for supercapacitor and capacitive deionization

Abstract

An efficient method that utilizes simple techniques, easy operation, and low-cost production to create flexible graphene-based materials is a worthy practical challenge. A rapid strategy for preparing flexible, functional graphene oxide (GO) is introduced using GO-ethanol dispersion filtration. The filtration process is highly efficient and drying time is significantly reduced by employing ethanol as solvent, due to the fact that ethanol is a volatile liquid. Freestanding GO papers can be harvested with ultralarge size (700 cm 2), color variety, and writable characteristics. After reduction, N-doped graphene (NDG) papers still maintain good foldability with improved electric conductivity and porous structure. When used as an electrode for a supercapacitor, the flexible NDG paper device demonstrates good electrochemical performance even with size expansion and extreme double folding. Moreover, this NDG paper capacitor device shows a good electrosorption performance for capacitive deionization of sulfate and chromate in groundwater system. These flexible GO and NDG papers promise potential to facilitate the production of graphene-based materials for practical applications in energy and environmental related fields.

Controllable Design and Preparation of Hollow Carbon-Based Nanotubes for Asymmetric Supercapacitors and Capacitive Deionization

“…Polyvinyl pyrrolidone (PVP, MW 30,000, Sigma Aldrich), 3-aminophenol (C 6 H 7 NO, AR, Macklin), and other reagents were used without further purification. Activated carbon fiber and Ni foam (loading substrate and current collectors) were treated and cleaned according to our reported methodology . The schematic illustration displayed the detailed synthetic processes of HCT and NHCT (Scheme a).…”

“…Structural and morphological characterizations of different materials and electrochemical and CDI tests are given in Supporting Information and our previous studies, including general characterizations: X-ray diffraction (XRD); scanning electron microscopy (SEM); transmission electron microscopy (TEM); specific surface area (SSA); Raman spectrum and X-ray photoelectron spectroscopy (XPS); and detailed electrochemical and CDI tests with related equations.…”

“…With the continuous demand for traditional fuels and the increasingly serious environmental problems, there is an urgent need to develop sustainable and clean energy storage. − Supercapacitors possess the advantages of fast charging/discharging process and long cycling stability and have been widely regarded as renewable resources by many researchers. − Electrode materials are the crucial factor in influencing the electrochemical performance of supercapacitors, and carbon-based materials have been commonly used because of their superiority of stable property, low cost, and eco-friendly features. − However, most traditional carbon materials are limited in their promotion of capacity due to their heterogeneous morphology, trend aggregation, and low diffusion efficiency for ions. , The one-dimensional (1D) structure means that electrode materials possess an almost linear shape in nanoscale with regular homogeneous morphology, such as nanowire, nanorod, nanotube, , and nanofiber, due to the directional conduction of electrons for decreasing the axial transmission path. , The carbon nanotube (CNT), a typical 1D carbon-based material, has attracted considerable interest because of its abundant applications including in catalysis, adsorption, , sensors, and energy storage . Nevertheless, application of the CNT is largely limited because of its disadvantages such as expensive preparation cost, special synthesis technique, poor aqueous solubility, and deficient channel diameter. , …”

Carbon Nanocoil-Supported Three-Dimensional Structure of Nickel–Cobalt Nitrides as the Electrode Material for Supercapacitors

“…Therefore, pseudocapacitors store a substantial amount of charges as compared to EDLCs. For a large-scale commercial production, devoted efforts are required to synthesize electrode materials with economical synthesis procedures and desirable structures for SC systems. ,, Additionally, pseudocapacitive materials sustain their performance at high rates even after several cycles, which makes them favorable candidates for commercialization. ,,,, Furthermore, due to the remarkable conversion reaction mechanism and high capacity of the pseudocapacitive electrode materials, they have been considered ideal candidates among the commonly reported electrode materials. , Previously, bimetallic oxides (such as Ni–Mn) and transition-metal oxides (such as Fe 2 O 3 , Co 3 O 4 , and MnO 2 ) have been utilized as electrode materials, primarily due to enriched oxidative and reductive reactions. , Owing to the poor electrical conductivities and bad cyclic stability of the aforementioned electrode materials, their potential use for practical applications is limited. ,, To overcome the above-mentioned inherent limitations, researchers targeted the transition-metal nitrides (TMNs) (e.g., Co 4 N, CrN, Ni 3 FeN, and Fe 2 N) and metal oxinitrides (TiN x O y ) . Comparatively, TMNs possess exceptional properties such as diverse chemical valence states, excellent conductivity (4000–55,500 S cm –1 ), better sustainability, and moderately high capacity which have made them the perfect choice as electrode materials for practical energy storage devices. ,− Furthermore, due to the higher electronic energy states of 2p orbitals of nitrogen (N) in TMNs, the band gap in TMNs has been narrowed, hence offering a high electron conductivity …”

“…15,16 Previously, bimetallic oxides (such as Ni−Mn) 17 and transition-metal oxides (such as Fe 2 O 3 , 18 Co 3 O 4 , 19 and MnO 2 20 ) have been utilized as electrode materials, primarily due to enriched oxidative and reductive reactions. 10,21 Owing to the poor electrical conductivities and bad cyclic stability of the aforementioned electrode materials, their potential use for practical applications is limited. 15,22,23 To overcome the abovementioned inherent limitations, researchers targeted the transition-metal nitrides (TMNs) (e.g., Co 4 N, 24 CrN, 25 Ni 3 FeN, 26 and Fe 2 N 27 ) and metal oxinitrides (TiN x O y ).…”