To solve the aforementioned problems, emerging graphene agglomerates with crumpled morphologies obtained by the stacking of graphene sheets seem to be promising for increasing the packing density and energy density in energystorage devices. [ 23,24 ] Unfortunately, they usually exhibit a rather low packing density, and consequently a relatively low volumetric capacity. Additionally, the closely stacked graphene agglomerate electrodes generally decrease the ion-accessible surface area and electrolyte ion diffusion, which inevitably compromises its lithium storage capacity. Thus, both a high density and porous structure should be taken into consideration when seeking a strategy for the synthesis of novel carbon-based LIB anodes.Recently, holey graphene, as a new class of graphene derivatives, has attracted extensive attention because of its high intrinsic electrical conductivity, open ion channels, and edge activity useful for applications in electrochemistry-related fi elds. [ 8,25 ] In our previous study, we have demonstrated a lightweight porous graphene foam as advanced electrode material for electrochemical processes (e.g., hydrogen evolution reaction, oxygen reduction reaction, ethanol oxidation reaction, and as electrochemical capacitor). [26][27][28][29][30] Herein, we report a N-doped holey-graphene monolith (NHGM) with a dense microstructure and high density of 1.1 g cm −3 . The holey structure in the individual graphene sheets could not only provide effi cient diffusion channels for Li ions and a highly conductive pathway for electrons, but also provided more edges on the sheet to enhance Li intercalation. [ 31,32 ] NHGM was obtained by conjugating N-containing holey-graphene sheets into a 3D hydrogel, followed by evaporation of the trapped water under vacuum at room temperature and an annealing treatment under Ar atmosphere. This highly compact but porous architecture with heteroatom doping is favorable for ion diffusion, Li ion storage, and maximizing the LIB properties; the NHGM had a volumetric capacity of 1052 mAh cm −3 , which is nearly three times that of commercial graphite anodes (370 mAh cm −3 ), [ 33 ] and exhibited competitive characteristics over the existing Si-based and carbon/sulfur hybrid electrode materials (see Table S1 in the Supporting Information). This makes our graphene-based electrode material an important step toward practical applications.To prepare the N-doped, high-density, holey-graphene monolith (NHGM), we fi rst produced the N-containing holeygraphene hydrogel (NHGH) by a one-pot hydrothermal process with simultaneous etching of nanopores in the graphene sheets and co-assembly of graphene and pyrrole to form a 3D hydrogel. During the hydrothermal process, a controlled amount of H 2 O 2

Similar to the paper-making process, the effi cient fl ame retardant graphene paper is conveniently obtained by using graphene oxide (GO) and hexachlorocyclotriphosphazene (HCCP) aqueous pulp. The "paper pulp" can also conceivably be used as ink to make other hydrophilic fi lms become fl ame retardant paper. Further, the as-prepared reduced GO-HCCP paper (RGO-HCCP paper), compared with GO-HCCP paper, can maintain its intact structure for a longer time in an ethanol fl ame. As a consequence of these preparation methods, the bearing temperature of the as-prepared graphene papers shows a signifi cant increase.

Traditional flame-retardant materials often show poor tolerance to oxidants, strong acidic/alkaline reagents, organic solvents, along with toxicity problems. Herein, highly fire-retardant ultralight graphene foam has been developed, which possesses not only ultralight and compressible characteristics but also efficient flame-retardant properties, outperforming those traditional polymer, metallic oxide, and metal hydroxide based flame retardant materials and their composites. The newly developed unconventional refractory materials are promising for specific applications as demonstrated by the observed high temperature resistant microwave absorption capability.

In this study, N,P co-doped graphene (NPG) was prepared by a one-step pyrolysis using a mixture of graphene oxide and hexachlorocyclotriphosphazene (HCCP), in which HCCP was used as both the N and P source. Furthermore, it is shown that NPG electrodes, as efficient metal-free electrocatalysts, have a high onset potential, high current density, and long-term stability for the oxygen reduction reaction.

No abstract

With the development of the Internet, the use of hybrid learning is spreading in colleges and universities across the country. The urgent problem now is how to improve the quality of hybrid learning; specifically, how to improve the learning effect of students under an online learning mode. In this paper, we build an online learning path model by exploring the big data of students' online learning processes. The model can be used to find excellent learning paths. Based on students’ learning habits, we recommend personalized and excellent learning paths with a high degree of similarity for general students. By comparison, experimental results indicate that our proposed methods not only provide sound recommendations regarding appropriate learning paths with significantly improved learning results in terms of accuracy and efficiency, but our methods also provide support that helps to improve teaching quality, promote personalized learning and target teaching.

Based on the micro-data of 79 listed companies in the Chinese marine ship industry chain from 2015 to 2019, this paper calculates the comprehensive technical efficiency (TE), pure technical efficiency (PTE), and scale efficiency (SE) of the upstream, midstream, and downstream of China’s marine ship industry chain by using a three-stage super-efficiency slacks-based model (SBM), and further analyzes the weak links in industrial chain efficiency and their influencing factors. It is shown that (i) the TE and PTE of the upstream, midstream, and downstream of China’s marine ship industry chain are in a “V”-shaped distribution, high at both ends and low in the middle, but that the SE is ranked as follows: upstream > midstream > downstream. In addition, the PTE is the main factor which hinders the improvement of TE in the industrial chain. (ii) The environmental variables have significant impacts on industrial chain efficiency. When the influences of environmental variables and random error terms are excluded, the industrial chain efficiency changes significantly. The values of SE and TE decrease significantly, and the distribution characteristic of TE changes. However, the PTE is still in a “V”-shaped distribution and appears to be the main driving force for the progress of TE. (iii) China’s marine ship industry chain has obvious weak links in terms of efficiency, and the midstream and downstream areas need to focus on development. Each link of the industry chain has high coupling and low coordination, and they are all closely related to each other, but the coordination ability is insufficient. The industrial chain in terms of efficiency and coordinated development can still be improved.