Preparation of Three-Dimensional Porous Graphene by Hydrothermal and Chemical Reduction with Ascorbic Acid and its Electrochemical Properties

Three-dimensional porous graphene (3D-PG) has attracted much attention due to its excellent electrochemical performance. Chemical reduction is one of common methods for preparing porous graphene. In order to develop a green and facile method for preparing three-dimensional porous graphene, in this paper, 3D-PG was fabricated by reduction of graphene oxide (GO) with ascorbic acid (AA) as reductant in hydrothermal condition based on non-toxic, non-flammable and mild reducing performance of ascorbic acid. It was found that the size and distribution of pores could be controlled by the reduction time and the concentration of AA in the solution. The pore sizes in R0, R1 and R2 were in the range of 0.5-1 μm, 1-1.5 μm, and 1.5-3 μm, respectively. It was found that the average pore size and volume increased along with the amount of reductants. Under optimal conditions - a reaction time of 20 h and a ratio of GO to AA=1 : 1 - the CV area of the so-obtained sample R1-20 at 100 mV was 0.06 and the specific capacitance of the 3D-PG electrode reaches 153.5 F ⋅ g^-1 , which is suitable for use in supercapacitors.

Biomimetic Turbinate-like Artificial Nose for Hydrogen Detection Based on 3D Porous Laser-Induced Graphene

Inspired by the turbinate structure in the olfaction system of a dog, a biomimetic artificial nose based on 3D porous laser-induced graphene (LIG) decorated with palladium (Pd) nanoparticles (NPs) has been developed for room-temperature hydrogen (H₂) detection. A 3D porous biomimetic turbinate-like network of graphene was synthesized by simply irradiating an infrared laser beam onto a polyimide substrate, which could further be transferred onto another flexible substrate such as polyethylene terephthalate (PET) to broaden its application. The sensing mechanism is based on the catalytic effect of the Pd NPs on the crystal defect of the biomimetic LIG turbinate-like microstructure, which allows facile adsorption and desorption of the nonpolar H₂ molecules. The sensor demonstrated an approximately linear sensing response to H₂ concentration. Compared to chemical vapor-deposited (CVD) graphene-based gas sensors, the biomimetic turbinate-like microstructure LIG-gas sensor showed ∼1 time higher sensing performance with much simpler and lower-cost fabrication. Furthermore, to expand the potential applications of the biomimetic sensor, we modulated the resistance of the biomimetic LIG sensor by varying laser sweeping gaps and also demonstrated a well-transferred LIG layer onto transparent substrates. Moreover, the LIG sensor showed good mechanical flexibility and robustness for potential wearable and flexible device applications.

Self-Organized 3D Porous Graphene Dual-Doped with Biomass-Sponsored Nitrogen and Sulfur for Oxygen Reduction and Evolution

3D graphene-based materials offer immense potentials to overcome the challenges related to the functionality, performance, cost, and stability of fuel cell electrocatalysts. Herein, a nitrogen (N) and sulfur (S) dual-doped 3D porous graphene catalyst is synthesized via a single-row pyrolysis using biomass as solitary source for both N and S, and structure directing agent. The thermochemical reaction of biomass functional groups with graphene oxide facilitates in situ generation of reactive N and S species, stimulating the graphene layers to reorganize into a trimodal 3D porous assembly. The resultant catalyst exhibits high ORR and OER performance superior to similar materials obtained through toxic chemicals and multistep routes. Its stability and tolerance to CO and methanol oxidation molecules are far superior to commercial Pt/C. The dynamics governing the structural transformation and the enhanced catalytic activity in both alkaline and acidic media are discussed. This work offers a unique approach for rapid synthesis of a dual-heteroatom doped 3D porous-graphene-architecture for wider applications.

Facile Synthesis of Hierarchical Mesoporous Honeycomb-like NiO for Aqueous Asymmetric Supercapacitors

Three-dimensional (3D) hierarchical nanostructures have been demonstrated as one of the most ideal electrode materials in energy storage systems due to the synergistic combination of the advantages of both nanostructures and microstructures. In this study, the honeycomb-like mesoporous NiO microspheres as promising cathode materials for supercapacitors have been achieved using a hydrothermal reaction, followed by an annealing process. The electrochemical tests demonstrate the highest specific capacitance of 1250 F g(-1) at 1 A g(-1). Even at 5 A g(-1), a specific capacitance of 945 F g(-1) with 88.4% retention after 3500 cycles was obtained. In addition, the 3D porous graphene (reduced graphene oxide, rGO) has been prepared as an anode material for supercapacitors, which displays a good capacitance performance of 302 F g(-1) at 1 A g(-1). An asymmetric supercapacitor has been successfully fabricated based on the honeycomb-like NiO and rGO. The asymmetric supercapacitor achieves a remarkable performance with a specific capacitance of 74.4 F g(-1), an energy density of 23.25 Wh kg(-1), and a power density of 9.3 kW kg(-1), which is able to light up a light-emitting diode.