The mid-, near-, and far-infrared (IR) spectra of synthetic, single-phase calcium silicate hydrates (C-S-H) with Ca/Si ratios (C/S) of 0.41-1.85, 1.4 nm tobermorite, 1.1 nm tobermorite, and jennite confirm the similarity of the structure of these phases and provide important new insight into their H 2 O and OH environments. The main mid-IR bands occur at 950-1100, 810-830, 660-670, and 440-450 cm −1 , consistent with single silicate chain structures. For the C-S-H samples, the mid-IR bands change systematically with increasing C/S ratio, consistent with decreasing silicate polymerization and with an increasing content of jennite-like structural environments of C/S ratios >1.2. The 950-1100 cm −1 group of bands due to Si-O stretching shifts first to lower wave number due to decreasing polymerization and then to higher wave numbers, possibly reflecting an increase in jennite-like structural environments. Because IR spectroscopy is a local structural probe, the spatial distribution of the jennite-like domains cannot be determined from these data. A shoulder at ∼1200 cm −1 due to Si-O stretching vibrations in Q 3 sites occurs only at C/S ≤ 0.7. The 660-670 cm −1 band due to Si-O-Si bending broadens and decreases in intensity for samples with C/S > 0.88, consistent with depolymerization and decreased structural order. In the near-IR region, the combination band at 4567 cm −1 due to Si-OH stretching plus O-H stretching decreases in intensity and is absent at C/S greater than ∼1.2, indicating the absence of Si-OH linkages at C/S ratios greater than this. The primary Si-OH band at 3740 cm −1 decreases in a similar way. In the far-IR region, C-S-H samples with C/S ratio greater than ∼1.3 have increased absorption intensity at ∼300 cm −1 , indicating the presence of CaOH environments, even though portlandite cannot be detected by X-ray diffraction for C/S ratios <1.5. These results, in combination with our previous NMR and Raman spectroscopic studies of the same samples, provide the basis for a more complete structural model for this type of C-S-H, which is described.

A complex impedance model for spherical particles was used to determine the lithium ion diffusion coefficient in graphite as a function of the state of charge (SOC) and temperature. The values obtained range from of 1.12 ϫ 10 Ϫ10 to 6.51 ϫ 10 Ϫ11 cm 2 /s at 25ЊC for 0 and 30% SOC, respectively, and for 0% SOC, the value at 55ЊC was 1.35 ϫ 10 Ϫ10 cm 2 /s. The conventional potentiostatic intermittent titration technique (PITT) and Warburg impedance approaches were also evaluated, and the advantages and disadvantages of these techniques were exposed.

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Catalysts play an important role in the energy conversion reaction process.

Graphene oxide (GO) is promising for a variety of applications due to its excellent dispersibility and processability. However, current chemical oxidation routes have several drawbacks, including the use of explosive oxidizing agents, residual metal ions contaminations, and the creation of irreparable hole defects on the GO sheet. The electrochemical exfoliation and oxidation of graphite is a potentially greener approach without the need for extensive purification steps. Most reported electrochemical methods employ a single preformed bulk graphite as electrode, which limits their scalability, reproducibility, and degree of oxidation. Herein, we reported a novel mechanically assisted electrochemical method to produce graphene oxide directly from graphite flakes. The electrochemically derived graphene oxide (EGO) shows a good degree of oxidation but with less physical defects than chemically derived graphene oxide (CGO). EGO has good dispersibility in water and various solvents and, in particular, displays better long-term stability in ethanol when compared with CGO. Notably, unlike conventional CGO, EGO can undergo facile thermal conversion at 200 °C in air to conductive thermally processed EGO, which is highly desirable for heat/chemical-sensitive applications.

Reproducible and in-depth studies of the electrochemical graphite intercalation and oxidation processes were carried out with the use of an electrochemical Tee-cell setup. The electrochemical method allowed simpler and greater controllability over the level of oxidation/functionalization, relative to the commonly employed chemical oxidation approach (e.g. the modified Hummers method). Extensive characterization was carried out to understand the properties of the electrochemically-derived graphite oxide (EGrO) and it was found that the abundance of each functionality is highly dependent on the electrochemical reaction time or by varying the concentration of the electrolyte (perchloric acid) employed.Notably, the amount of oxygen functional groups on EGrO could be as high as 30 wt.%, but the degree of oxidation did not proceed beyond the generation of carbonyl species. The controllable oxidation level of the EGrO makes it an attractive precursor for many applications, such as electronics and nanocomposites.

Since Sony introduced the first commercial cell in 1990 that used a carbon material in lieu of lithium metal as the negative electrode, 1 rechargeable Li-ion batteries have become readily available worldwide. Of various carbon materials, graphite is favored because it exhibits a high specific capacity, a most desirable charge potential profile, and superior cycling behavior. However, the irreversible reactions that take place with lithium during the first cycle have been one of the very persistent problems associated with the use of graphite. In commercial Li-ion cells, the loss of lithium due to these irreversible reactions is normally compensated for by using excess cathode material, however, this leads to a decrease in the specific energy density and thus an increase in the cell cost. 2,3 These irreversible reactions can also cause gas evolution, which may result in some very serious safety issues, such as cell can buckling, cell venting, electrolyte spillage, and even fire. 2,4 It is widely known 2-5 that the irreversible capacity can originate from electrolyte decomposition followed by the formation of a solid electrolyte interface (SEI) film on the external surface of the graphite. However, it can also arise from solvated lithium intercalation between the graphene layers and subsequent reduction of the solvent, 6-7 because the formation of a solvated lithium/graphite compound like Li x (sol) y C 6 is more favorable than the formation of Li x C 6 during insertion. 6 The irreversible capacities in both cases are largely dependent on the external surface area of the electrode, 6 because the exposed surface is where the irreversible reactions take place. In fact, it has been shown that the irreversible capacity associated with the edge surfaces of graphite is substantially larger than that associated with the basal plane surfaces due to solvent cointercalation into the layer spacing. 7 The irreversible capacity associated with the use of graphite also varies considerably with different electrolytes, and especially with different solvents. It has been shown 7-9 that the irreversible reactions are worse in propylene carbonate (PC)-based electrolyte than in ethylene carbonate (EC)-based electrolyte, and PC alone can cause severe degradation of the graphite structure by a process called "exfoliation." 7-11 The results by Ogumi et al. 12 indicated that PC begins to decompose at ca. 1 V vs. Li/Li ϩ and continues to decompose during the remainder of the intercalation process. It has further been suggested that this decomposition occurs continuously without forming a stable passive SEI layer on the edge surfaces of the graphite particles. [7][8][9][10][11] The net effect is that the PC solvent continuously cointercalates with Li-ions into the graphene layers and subsequently reduces, which gives rise to a large irreversible capacity during cycling. 9,11 Nevertheless, PC is still attractive for use as an electrolyte in Li-ion batteries, especially for low-temperature operation, because of its high salt solubility and lo...