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Exfoliated graphite (EG) is promising oil sorbent as well as an intermediate product for the preparation of flexible graphite films (FGFs). It has been a critical challenge to energy conservation and pollution abatement for the traditional EG production technique. Here, we propose a simple and effective preparation method to acquire EG in which flake graphite is intercalated and exfoliated at room temperature, not involving any pollutant emission. The influence factors in the preparation process were explored, such as the amount of H2SO4 and H2O2, the temperature for the preparation of room temperature exfoliated graphite (RTEG). In contrast to the EG by high temperature exfoliation (HTEG), RTEG exhibits a homogeneous structure and a significantly increased volume and surface area. Moreover, EG blocks with high oil sorption capacity and excellent reuse performance can be obtained by RTEG method. Especially, FGFs fabricated by RTEG has high flexibility, thermal conductivity and electrical conductivity. It suggests that this environment-friendly technology is suitable for large-scale industrial implementation of graphite-based oil sorbents and flexible materials.

Herein, oriented boron nitride (BN)/alumina (Al2O3)/polydimethylsiloxane (PDMS) composites were obtained by filler orientation due to the shear-inducing effect via 3-D printing. The oriented BN platelets acted as a rapid highway for heat transfer in the matrix and resulted in a significant increase in the thermal conductivity along the orientation direction. Extra addition of spherical Al2O3 enhanced the fillers networks and resulted in the dramatic growth of slurry viscosity. This, together with filler orientation induced the synergism and provided large increases in the thermal conductivity. A high orientation degree of 90.65% and in-plane thermal conductivity of 3.64 W/(m∙K) were realized in the composites with oriented 35 wt% BN and 30 wt% Al2O3 hybrid fillers. We attributed the influence of filler orientation and hybrid fillers on the thermal conductivity to the decrease of thermal interface resistance of composites and proposed possible theoretical models for the thermal conductivity enhancement mechanisms.

Efficient thermal dissipation is one of the most critical factors constraining the development of modern microelectronic devices. Placing vertically aligned carbon nanotubes (VACNTs) with anisotropic thermal conductive between high-power devices and heat sink such as copper plate can improve the interfacial thermal conductance. Due to the limited contact area between CNTs and the surface of the devices, direct use of ACNTs as thermal interface material fails to meet people’s expectations. Here, we employ reduced graphene oxide (rGO) as the substrate for the growth of CNT arrays. VACNTs grown on rGO (rGO-ACNT) by chemical vapor deposition are then used as thermal conducting filler in epoxy resin. Compared with direct contact between CNT and the interface, using CNT and reduced graphene oxide junction to form contact with the surface can improve heat transfer efficiency. The resultant composite film exhibited excellent thermal conductivity at 9.62 W m−1 K−1 along the thickness direction. The obtained rGO-ACNT and its composite present higher thermal conductivity and heat transfer ability than ACNT. This strategy offers an insight into the easy preparation of flexible and highly thermal conductive composite materials, which may enable potential applications in advanced electronic devices.

Aromatic polyimide (PI)-based graphite nanofibers were obtained from the graphitization of graphene oxide (GO)-doped electrospun PI nanofibers. GO improves the PI molecular orientation, crystalline structure and thermal conductivity of the resulting nanofibers. The degree of PI molecular orientation in the nanofibers is increased by the GO during fiber preparation. This improvement in molecular orientation produces an increase in the thermal conductivity of the graphite nanofibers, and the addition of only 0.1% GO has a significant effect. The GO not only affects the thermal conductivity, but improves the PI molecular orientation and its role as nucleation centers during graphitization. This approach and the resulting high thermal conductivity materials show great potential for practical applications.

Fe—N—C materials have shown a promising nonprecious oxygen reduction reaction (ORR) electrocatalyst yet their active site structure remains elusive. Several previous works suggest the existence of a mysterious axial ligand on the Fe center, which, however, is still unclarified. In this study, the mysterious axial ligand is identified as a hydroxyl ligand on the Fe centers and selectively promotes the ORR activities depending on different Fe—N4—C configurations, on which the adsorption free energy of the hydroxyl ligand also differs greatly. The selective formation of hydroxyl ligand on specific Fe—N—C configurations can resolve contradictories between previous theoretical and experimental results regarding the ORR activities and associated active configurations of Fe—N—C catalysts. It also explains the pH‐dependent ORR activities and, moreover, a previously unreported pH‐dependent poisoning kinetics of the Fe—N—C catalysts., An axial hydroxyl ligand on Fe—N—C catalysts under oxygen reduction reaction (ORR) is revealed by using density functional theory calculations combined with electrochemical experiments. This uncovered ligand can close the gap between recent theoretical and experimental results regarding the active sites of Fe—N—C catalysts. It also leads to pH‐dependent ORR activities and pH‐dependent poisoning by thiocyanates.

Porous Fe3O4/carbon microspheres (PFCMs) were successfully fabricated via a facile electrospray method and subsequent heat treatment, using ferrous acetylacetonate, carbon nanotubes (CNTs), Ketjen black (KB), polyvinylpyrrolidone (PVP), and polystyrene (PS) as raw materials. The porous carbon sphere framework decorated with well-dispersed CNTs and KB exhibits excellent electronic conductivity and acts as a good host to confine the Fe3O4 nanoparticles. The abundant mesopores in the carbon matrix derived from polymer pyrolysis can effectively accommodate the volume changes of Fe3O4 during the charge/discharge process, facilitate electrolyte penetration, and promote fast ion diffusion. Moreover, a thin amorphous carbon layer on the Fe3O4 nanoparticle formed during polymer carbonization can further alleviate the mechanical stress associated with volume changes, and preventing aggregation and exfoliation of Fe3O4 nanoparticles during cycling. Therefore, as anode materials for lithium-ion batteries, the PFCMs exhibited excellent cycling stability with high specific capacities, and outstanding rate performances. After 130 cycles at a small current density of 0.1 A·g–1, the reversible capacity of the PFCM electrode is maintained at almost 1,317 mAh·g–1. High capacities of 746 and 525 mAh·g–1 were still achieved after 300 cycles at the larger currents of 1 and 5 A·g–1, respectively. The optimized structure design and facile fabrication process provide a promising way for the utilization of energy storage materials, which have high capacities but whose performance is hindered by large volume changes and poor electrical conductivity in lithium or sodium ion batteries.

Thermal interface materials composed of polymers and solid particles of high thermal conductivity have been used widely in electronic cooling industries. However, theoretical prediction of effective thermal conductivity of the composites remains as a crucial research topic. Theoretical modelings of the effective thermal conductivity of composites were based mainly on the analog between electric and thermal fields that satisfy Laplace equation under steady condition. Two approaches were employed, either by solving the Laplace equation or by equating the composite to a circuit network of conductors. In this study, the existing models obtained from these two approaches are first briefly reviewed. However, a close examination of the second approach reveals that there exists a paradox in this approach. To resolve this paradox, a statistical approach is then adopted. To this end, a mesoscopic ensemble that contains microscopic states is first constructed. The thermal conductivities of the microstates are identified by the principle of least action. A statistical parameter for each microstate is identified to characterize the effect of interface resistance on heat flow, as well as the connection between microstates. Effective thermal conductivity of the ensemble was then obtained from the variation principle that minimizes the standard deviation with optimal distribution of the parameter. The predictions by the present statistical model fit to experimental data with excellent agreement.

Metal dissolution and redeposition are considered to be the most important degradation mechanism for Pt-based fuel cell electrocatalysts. Understanding key factors mitigating the dissolution and migration under realistic proton-exchange-membrane (PEM) fuel cells is crucial for improving their performance and durability. Using ordered and disordered PtCo electrocatalysts, we address how structural ordering and particle size can affect the dissolution of Co/Pt and their redeposition into the membrane upon catalyst accelerated durability test in PEM fuel cells by statistical scanning transmission electron microscopy (STEM) and spectroscopic analysis. Consistent with the improved performance and durability, we observe that both Co and Pt dissolution were mitigated in the ordered PtCo catalyst compared to the disordered one. The suppressed Pt dissolution was evidenced from the relieved particle coarsening and significantly suppressed Pt redeposition/migration in the membrane after the durability test. Moreover, we reveal an optimum particle size range between 2–5 nm for ordered PtCo catalysts, which favors the highest structural ordering degree and hence the highest retention of Co. These results provide a rationale for implementing ordered Pt intermetallic electrocatalysts in PEM fuel cells and further particle size optimization for improved durability.

Graphene/polytetrafluoroethylene (PTFE)/polyoxymethylene (POM) composites were successfully prepared by high speed mixer and injection molding machine. As a consequence, graphene and PTFE covered at the surface of the POM powder evenly and the tribological performance of the composites is enhanced remarkably, especially the graphene content is 0.2%. In addition, the friction and wear behaviour of the composites is connection to the content of graphene, both of them will decrease at first and increase with the adding of graphene. In a word, this proposed method is simple and effective for mass production of graphene/PTFE/POM composites, and it is promising to be applied to fabricate many kinds of nanofillers modified POM composites.

Laser flash analysis (LFA) is a sophisticated method to access the thermal diffusivity of homogeneous planar samples with very little effort. LFA measurement on fiber-reinforced composites, however, often generates inconsistent results due to violation of homogeneous assumptions. We propose a computational method to reduce this inconsistency. The method compares the radiometer signals of one dimensional carbon fiber-reinforced composite from LFA measurement and the finite element simulation results to predict the interfacial thermal resistance and the axial thermal conductivity of carbon fiber. The thermal conductivities of the composite under different environmental temperature are obtained. Agreement between the simulation signal curves and the experiment signal curves is within 5% error during the main temperature rise. The method extends the functionality of LFA to measuring thermal conductivity of complex composite with known microscopic structure, and provides a way to estimate microscopic parameters and to evaluate macroscopic and microscopic effect of different preparation methods.

In this study, we report on a fundamental first-principles investigation of native point defects in spinel LiTi2O4, an alternative electrode material for lithium ion batteries (LIBs). Under O-rich conditions, Ti vacancy (VTi) and Li antisite (LiTi) are energetically favorable, but Ti interstitial (Tii) has highest formation energy and is hence unstable. While Li interstitial (Lii) is the most stable configuration in O-poor conditions, and O vacancy (VO), Ti interstitial (Tii), Li antisite (LiTi) and Ti antisite (TiLi) have almost the same formation energies, suggesting spontaneous formation of defect complexes. According to the calculated electronic structures of defects, no localized states are found in the gap between the O 2p and Ti t2g states, which is considerable related to the charge compensation process between O and Ti ions. Besides, Li vacancy (VLi) and Li interstitial (Lii) are the most stable defect types with negligible structural changes, while other defects will induce large octahedral disorders and suppress Li ions mobility. These results not only reveal the original defect information of LiTi2O4, but also provide practical guidance to the development of this material.

It has been indicated that anatase TiO2 is a promising anode material for lithium ion power battery from many previous researches. Whereas, in this work, we find that the anatase TiO2, when used as an anode for lithium ion battery, has high catalytic activity to initiate the decarboxylation reaction of electrolyte solution, resulting in the large generation of sole gaseous component, CO2. The ROLi species and the new phase of flake-like Li2TiF6 material are the main reaction products between anatase TiO2 and LiPF6 based electrolyte solution. This work provides important and urgent information that the surface chemistry of anatase TiO2 used as the anode material of lithium ion battery must be modified to suppress its catalytic activity for the decomposition of solvents.

Six samples of α-MnO2 with different K ion contents are synthesized by using KMnO4 and Mn(CH3COO)2·4H2O with different pH values at room temperature. The samples are labeled as Mx where x denotes the pH value. The anomalous effect of K ion content on the electrochemical capacitance properties of amorphous MnO2 is investigated systematically. It is found that with the increase of the K ion content, the MnO2 nanospheres form a more dense aggregates, the surface area dramatically decreases from 273 (M2) to 14 m2 g−1 (M12), and pore volume decreases from 0.349 (M2) to 0.014 cm3 g−1 (M12). The specific capacitance (SC) is decreased by 17.6% from 157 (M2) to 131 F g−1 (M12). In addition, the SC values are greatly influenced by the molar ratio of K to Mn in the range of 0–0.4. And it is found that part of K ions in the MnO2 tunnels can be replaced by Na ions during electrochemical reaction. Finally, an appropriate explanation of the effect of K ion content on the SC values is provided.

A small amount of cations such as Li + , Na + , K + , or NH 4 + is required to stabilize the tunnels during the formation of MnO 2 . Here, the effect of the content of K ion on crystalline state and capacitance behavior of MnO 2 are investigated. It is found that with the content of K ion increasing, manganese dioxide is more likely to maintain amorphous, while adding Li + , Na + , or NH 4 + has no such effect. Adding K ion not only delays the conversion of manganese dioxide crystalline, but also delays the phase transformation temperature, which causes the big difference of specific capacitance value from 58 F g −1 for H2/400 to 124 F g −1 for K12/400. Furthermore, the morphology, special surface area, and pore data change dramatically from H2/400 to K12/400. These results have important implications for the characterization of MnO 2 in supercapacitor applications.

The lithium ion batteries using Li4Ti5O12 as the anode material are easily being inflated during charge and discharge, which, however, does not occur in the batteries using graphite as the anode material. The high reduction reactivity of electrolyte on the Li4Ti5O12 material may be the main reason. In this work, the reduction reactivities of electrolyte on the uncoated and carbon-coated Li4Ti5O12 electrodes are compared for the first time. The results show that the reduction decomposition of electrolyte does occur on the uncoated Li4Ti5O12 electrode at around 0.7 V, while it only takes place at the first cycle on the carbon-coated Li4Ti5O12 electrode. The carbon coating layers cover the catalytic active sites of Li4Ti5O12 particles and separate the Li4Ti5O12 particles from the electrolyte. A successive solid electrolyte interface (SEI) film is formed on the carbon layer during the formation process, which can prevent the further reduction decomposition of electrolyte at around 0.7 V. The impurity phases of rutile and anatase TiO2 do not influence the reduction reactivity of electrolyte. This work is not only important to understand the reduction decomposition mechanism of electrolyte on the Li4Ti5O12 electrode, but also provides an effective solution to suppress the reduction decomposition of electrolyte in the batteries.

Li4Ti5O12 anode material is synthesized using TiO2 with different crystal structure as titanium source by solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical test methods are applied to characterize the effects of TiO2 crystal structure on the structure, morphology and electrochemical performance of Li4Ti5O12. Results show that the reaction of TiO2 with Li2CO3 is an exothermic behavior. The reactivity of TiO2 with Li2CO3 gradually decreases and the particles size of Li4Ti5O12 increases with the TiO2 crystal structure changing from amorphous to rutile. The TiO2 crystal structure has a slight influence on the reversibility of Li4Ti5O12, while the specific capacities of Li4Ti5O12 at different current densities decreases obviously with the TiO2 crystal structure changing from amorphous to rutile and the sample using amorphous TiO2 as titanium sources shows highest specific capacity. The capacity retentions of all Li4Ti5O12 samples are above 97% after 50 cycles and these materials show good cycle performance. The TiO2 crystal structure has not large effects on the cycling performance of Li4Ti5O12 material.

The structural and thermal stabilities of the layered Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathode materials under high rate cycling and abusive conditions are investigated using the commercial 18650 Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 /graphite high power batteries. The Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 materials maintain their layered structure even when the power batteries are subjected to 200 cycles with 10 C discharge rate at temperatures of 25 and 50 °C, whereas their microstructure undergoes obvious distortion, which leads to the relatively poor cycling performance of power batteries at high charge/discharge rates and working temperature. Under abusive conditions, the increase in the battery temperature during overcharge is attributed to both the reactions of electrolyte solvents with overcharged graphite anode and Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathode and the Joule heat that results from the great increase in the total resistance ( R cell ) of batteries. The reactions of fully charged Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 cathodes and graphite anodes with electrolyte cannot be activated during short current test in the fully charged batteries. However, these reactions occur at around 140 °C in the fully charged batteries during oven test, which is much lower than the temperature of about 240 °C required for the reactions outside batteries.

The co-existence of two mechanisms, the surface chemisorption mechanism (SCM) and the tunnel storage mechanism (TSM), for the charge storage of MnO 2 is investigated. Sample α-MnO 2 whose tunnels (2 × 2) are almost vacant is synthesized by chemical co-precipitation technique. To verify whether the charge storage of as-prepared α-MnO 2 involves the charges based on the SCM besides the TSM, Ba 2+ and K + are intercalated into the tunnels of α-MnO 2 by refluxing and samples Ba-MnO 2 and K-MnO 2 are obtained, respectively. By powder X-ray diffraction, ICP and the extraction test, it is confirmed that Ba 2+ and K + occupy the tunnels and are difficult to remove. By electrochemical analyses, we have found that the charge storage of Ba-MnO 2 and K-MnO 2 basically depends on the SCM, as Ba 2+ and K + stabilized in the tunnels in advance block the intercalation/deintercalation of cations from the electrolyte. Thus, it can be inferred that for α-MnO 2 two mechanisms contribute to the charge storage. The contributions of α-MnO 2 's mechanisms are estimated. The charges based on the TSM predominantly account for 81.2–89.9% of the total charges. The charges on the SCM may contribute to 7.9–16.8% and are not negligible. The charges from double-layer capacitance may be negligible, since it is only 1.1–4.1%.

We synthesized three kinds of Pt-Ru/C catalysts (denoted as a, b, and c) through conventional polyol process by heating the reaction solutions to different temperatures (120, 160 and 180 °C, respectively) and the fourth kind of catalyst (denoted as d) through a modified polyol process at 180 °C. By using scanning transmission electron microscopy combined with energy dispersive X-ray line analysis, we found that a higher reaction temperature resulted in more uniform particle-compositions of the Pt-Ru catalysts, which could be ascribed to the influence of temperature on the reduction rates of metal ions. The Pt-Ru/C-a catalyst showed a bimodal particle-composition distribution, while the Pt-Ru/C-d catalyst showed the narrowest unimodal distribution due to the highest temperature throughout the reaction. X-ray diffraction showed that all the Pt-Ru/C catalysts exhibited low alloying degrees of Ru with Pt. From high resolution transmission electron microscopy, we confirmed that the un-alloyed Ru was present in an amorphous form (likely RuOx), and moreover, its distribution varied greatly in different catalysts. In the Pt-Ru/C-d catalyst, the amorphous RuOx intimately contacted with the Pt/Pt-rich alloy, forming nano-composite particles. The most uniform compositions of Pt-Ru particles in the Pt-Ru/C-d catalyst resulted in the highest electrocatalytic activity on methanol oxidation.

Bamboo-shaped carbon nanotubes (BCNTs), with a large amount of pentagon defects introduced in the walls, were explored as the support of high loaded Pt–Ru catalysts for the anode of direct methanol fuel cells (DMFCs) in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon black. By ethylene glycol reduction, Pt–Ru catalysts with a high loading (60 wt%) and uniform particle size of 2–3 nm were uniformly deposited on BCNTs; while 60 wt% Pt–Ru catalysts on CNTs resulted in significant agglomeration. The Pt–Ru/BCNT catalyst showed the highest activity on methanol oxidation in cyclic voltammetry and highest performance as the anode in a DMFC single cell. Such an enhancement was largely ascribed to an enhanced interaction of the introduced pentagon defects with Pt–Ru, which could promote a high loading and well dispersion of Pt–Ru catalysts and the charge transfer from Pt–Ru to the tubes. Keywords: Direct methanol fuel cells, Catalyst support, Carbon nanotubes, Pentagon defects, Pt–Ru catalysts, High loading

Different amounts of multi-walled carbon nanotubes (MWCNTs) are added to anode catalyst layer in the membrane electrode assemblies (MEAs) of direct methanol fuel cells (DMFCs). The MEA with 0.5 wt.% carbon nanotubes (CNTs) shows the best performance in DMFC. In the protonic conductivity tests, a 0.5 wt.% amount of MWCNTs results in the highest protonic conductivity. SEM and TEM observations show that a continuous and uniform distribution of Nafion ionomer layer is formed on the MWCNT surface. Therefore, the dispersed MWCNTs in the catalyst layer are considered to be helpful for developing the pathways of protons transport.

Manganese dioxide has been synthesized by a new simple self-reacting microemulsion method. The synthesized MnO 2 has been found to be amorphous structure containing a moderate amount of water by X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Particles in a spherical shape with about 4 nm in diameter have been observed by transmission electron microscopy. Cyclic voltammetic tests have been performed between −0.5 and 0.5 V versus Hg/Hg 2 SO 4 in 1 mol L −1 Na 2 SO 4 solution at sweep rates up to 50 mV s −1 . A specific capacitance value as high as 246.2 F g −1 was obtained, which was much higher than 146.5 F g −1 of MnO 2 prepared by chemical co-precipitation. After 600 cycles, only 6% decrease of specific capacitance was measured which indicated that such a material possesses good cycling property.

Destructive gas generation with associated swelling has been a major challenge to the large-scale application of lithium ion batteries (LIBs) made from Li(4)Ti(5)O(12) (LTO) anodes. Here we report root causes of the gassing behavior, and suggest remedy to suppress it. The generated gases mainly contain H(2), CO(2) and CO, which originate from interfacial reactions between LTO and surrounding alkyl carbonate solvents. The reactions occur at the very thin outermost surface of LTO (111) plane, which result in transformation from (111) to (222) plane and formation of (101) plane of anatase TiO(2). A nanoscale carbon coating along with a stable solid electrolyte interface (SEI) film around LTO is seen most effective as a barrier layer in suppressing the interfacial reaction and resulting gassing from the LTO surface. Such an ability to tune the interface nanostructure of electrodes has practical implications in the design of next-generation high power LIBs.