The gas diffusion layer (GDL) is an important component of the membrane electrode assembly (MEA) of fuel cells (FCs), which plays a key role in supporting the catalyst layer, collecting current, and transferring and redistributing materials. A conventional GDL consists of a backing layer (BL), typically made of commercial carbon paper or carbon cloth, but it still suffers from some challenges in terms of its high cost, narrow pore-size distribution, lack of flexibility, and poor conductivity. In that case, a micro-porous layer (MPL) is necessary for better gas/liquid management. In this study, a novel, flexible, integrated gas diffusion layer (GDL/CNT-CF) is successfully prepared through vacuum filtration by combining carbon fibres (CFs) with highly-dispersed multi-walled carbon nanotubes (MWCNTs) and polytetrafluoroethylene (PTFE) as a binder and water repellent. Scanning electron microscopy (SEM) combined with characterisation of conductivity, gas permeability, and porosity indicates that the highly-conductive MWCNTs in the GDL/CNT-CF are distributed in gradients in the CF networks, and can facilitate electron transport. Furthermore, the formed multi-level pore structure is beneficial to material distribution and the uniform distribution of PTFE contributes to improved water discharge. Therefore, it replaces the conventional diffusion layer consisting of carbon paper and MPL. When the GDL/CNT-CF is applied as the cathode, or both the cathode and anode, of a direct methanol fuel cell (DMFC), the maximum power density of the single cells is separately increased by 20% and 35% compared with that of a commercial GDL due to its excellent mass transfer performance.
A reduced graphene oxide (H-rGO)/TiO2–composite as a catalyst for photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO) was prepared by hydrothermal treating a dispersant of TiO2 nanoparticles with sizes of 5-10 nm and GO obtained by the Hummers method from coal-based graphite in water, which was compared with the M-rGO/TiO2 and GO/TiO2 composites by a wet mixing method. Results indicated that the TiO2 nanoparticles in H-TiO2@rGO were uniformly decorated on both sides of rGO sheet, forming a stacked-sheet structure while apparent aggregation of TiO2 nanoparticles was found for both M-rGO/TiO2 and GO/TiO2. H-rGO/TiO2 had the highest catalytic activity for degradation of Rh B and MO under visible light irradiation among the three, where incorporating rGO into TiO2 narrowed the band gap of TiO2, inhibited the recombination rate of electron–hole pairs and provided conductive networks for electron transfer.
Highly efficient synthesis of nitrogen-doped carbons with different porous structures is reported using shrimp shell as the carbon and nitrogen source, and its CaCO3 component as the hard template and the activator. The content of CaCO3 in shrimp shell can be tuned easily in the range of 0-100% by leaching with an acetic acid solution for different times. CaO derived from decomposition of CaCO3 acts as the activator and template to tailor the pore sizes of the carbons. CO2 derived from decomposition of CaCO3 also plays an activating role. Their specific surface areas, pore volumes, ratios of micropore volumes to total pore volumes can be adjusted in the range of 117.6-1137 m2 g-1, 0.14-0.64 cm3 g-1, and 0-73.4%, respectively. When used as the electrodes of supercapacitor, the porous carbon obtained with a leaching time of 92 min exhibits the highest capacitances of 328 F g-1 at 0.05 A g-1 in a 6 M KOH electrolyte and 619.2 F g-1 at 0.05 A g-1 in a 1 M H2SO4 electrolyte. Its corresponding energy density at a power density of 1470.9 W kg-1 is 26.0 Wh kg-1. This work provides a low cost method for fabricating porous carbons to fulfill the high-value-added use of biomass.
The radial structure of pre-oxidized fibers and its distribution directly affect the performance of the resulting carbon fibers. Optimizing the radial distribution of pre-oxidized structure and establishing the relationship between the pre-oxidized structure of polyacrylonitrile fibers and the mechanical properties of the final carbon fibers will help to optimize the pre-oxidation conditions in the preparation of high-performance carbon fibers. Herein, solid-state nuclear magnetic resonance spectroscopy, optical microscopy, thermogravimetric analysis, and mechanical tests were used to investigate the effect of the pre-oxidation reaction rate on the radial structural distribution of pre-oxidized fibers and the mechanical properties of the resulting carbon fibers. The pre-oxidation reaction rates were controlled by regulating the pre-oxidation temperature gradient. The results showed that the pre-oxidation degree of pre-oxidized fibers increased with both the overall and initial rates of pre-oxidation. With increasing the overall pre-oxidation reaction rate, the pre-oxidized structure was deepened into the core region of the fibers, the content of oxygen-containing functional groups increased, the thermal stability of the fibers decreased, the graphitization degree of the corresponding carbon fibers increased, but the density of the carbon fibers decreased and the mechanical properties of the carbon fibers were degraded. With increasing the initial reaction rate of pre-oxidation, the radial distribution of the pre-oxidation structure was effectively improved, the content of oxygen-containing functional groups of the pre-oxidized fibers increased slightly, their thermal stability was improved, the degree of graphitization and density of the final carbon fibers increased, and the tensile strength and tensile modulus of the final carbon fibers were markedly increased. A new type of carbon fibers with high strength, medium modulus and a relatively large diameter was obtained under the optimized pre-oxidation conditions.
Lithium sulfur battery has the advantages of high theoretical energy of 1675 mAh g-1, low price and environmental friendliness, which make it a very promising secondary battery. However, its cycling stability cannot meet the requirements of the industrialization due to the shuttle effect caused by the dissolution of polysulfides in the discharge process, the sulfur insulation and the volume expansion of the sulfur electrode. Graphene has excellent electrical conductivity, extremely large specific surface area, good mechanical flexibility, and thermal and chemical stability, so graphene and its derivatives are promising candidates to modify both the electrodes of the all-solid-state lithium-sulfur batteries and the separator. Herein, the mechanisms by which graphene and its derivatives inhibit the shuttle effect have been summarized. The graphene network is very favorable for the electron transfer, limiting volume expansion of sulfur electrodes and facilitating ion migration in all-solid-state lithium-sulfur batteries. As the modifiers of the separator, the hexagonal and layered structure of graphene and its derivates form the lithium ion transport channel and capture sulfur. The development strategy using graphene and its derivatives in lithium-sulfur batteries are proposed.
Micro/mesopore carbon spheres as electrode materials of supercapacitors were prepared by hydrothermal carbonization followed by KOH/NaOH activation using sucrose as the carbon precursor. The effects of KOH and NaOH activation parameters on the specific surface area, pore size distribution and electrochemical performance of the carbon spheres were investigated. Results indicate that the use of NaOH leads to the development of mesopores while the use of KOH is favorable to increase specific surface area and micropore volume. The pore size distribution of carbon spheres could be adjusted by varying the fraction of NaOH in the activation agent. A balanced capacitance and rate performance of the supercapacitor electrode in both 6 M KOH aqueous electrolyte and 1 M MeEt3NBF4/PC electrolyte is achieved when the carbonized product is activated at a mass ratio of NaOH+KOH/ carbonized product of 3∶1 with a NaOH/KOH mass ratio of 2∶1. As-prepared porous carbon delivers a capacitance of 235 F/g at 0.1 A/g and capacitance retention rate of 81.5% at 20 A/g in the 6 M KOH aqueous electrolyte. In 1 M MeEt3NBF4/PC, the cell based on the porous carbon delivers the highest energy and power output of 30.4 Wh kg-1 and 18.5 kW kg-1, respectively.