Pore formation in carbon materials

In this section, three case examples taken as representative for the development of different types of pores in carbon materials will be described. The first example to be considered constitutes a model for development of extrinsic nanopores by air oxidation. The second one concerns macropore development by graphite exfoliation. The third case example deals with intrinsic, two-dimensional slit pores formed between neighboring graphite layers by intercalation. 

Development of extrinsic nano-sized pores in glass-like carbon spheres 

The same procedure as for oxidation yield was applied to Sbet and to several porous textural parameters determined by the alpha method (total surface area, external surface area and micropore volume) on each sample oxidized in dry air. This led to the master curves at 673 K for the respective parameters shown on Fig. 21. All master curves for pore parameters were derived by using the same shift factors as for the oxidation yield (i.e., the same apparent activation energy). 

From this pore parameter analysis with air oxidation, it is deduced that pore development in glass-like carbon spheres proceeds principally through the progressive enlargement of ultramicropores to macropores through supermicropores and mesopores. 

In Fig. 22a) and b), exfoliation volume and mass loss are plotted against exfoliation temperature in two runs of experiments on the same residue compound [52]. In Fig. 22a), exfoliation volume increases with increasing exfoliation temperature. Two kinks are clearly observed in the dependence of exfoliation volume on exfoliation temperature, around 923 and 1073 K. Below 923 K and above 1073 K, the rate of exfoliation volume increase is smaller than in the intermediate temperature range. In Fig. 22b), mass loss occurs below 923 K and atove 1073 K, whereas in the intermediate temperature range only a slight increase in mass 

---

Pore Formation in Carbon Materials, Pore Characterization and... 

PORE FORMATION IN CARBON MATERIALS, PORE CHARACTERIZATION AND ANALYSIS OF PORES... 

TABLE 5.3 Classification of pore formation in carbon materials... 

Inagaki, M. and Tascon, J.M.D. (2006). Pore formation and control in carbon materials. In Activated Carbon Surfaces in Environmental Remediation (T.J. Bandosz, ed.). Elsevier, pp. 49—105. 

Solvent influence can cause a difference in the shape of the loop observed and hence the pores produced in a material (384). When an ethylene glycol/water solvent system is used in the preparation of LDH carbonate from coprecipitation, the material formed appears to have pores of regular geometry and relatively equal size throughout. A glycerol/water solution on the other hand produces material with mesopores of varying geometry. Analysis of the hysteresis loop that results from the latter solvent combination shows the initial formation of... 

In the sixth paper of this chapter, Kierzek et al., mainly focus on modeling of pore formation vs surface area growth phenomena upon activation of coal and pitch-derived carbon precursors. These authors briefly touch on other precursor carbons as well. The properties of newly synthesized materials are being looked at from the point of view of their application as active materials in the supercapacitor electrodes. Editors thought this work by the Institute of Chemistiy and Technology of Petroleum and Coal in Poland, could be of genuine interest to the practical developers of carbon materials for the supercapacitor industry. 

Microstructures of CLs vary depending on applicable solvenf, particle sizes of primary carbon powders, ionomer cluster size, temperafure, wetting properties of carbon materials, and composition of the CL ink. These factors determine the complex interactions between Pt/carbon particles, ionomer molecules, and solvent molecules, which control the catalyst layer formation process. The choice of a dispersion medium determines whefher fhe ionomer is to be found in solubilized, colloidal, or precipitated forms. This influences fhe microsfrucfure and fhe pore size disfribution of the CL. i It is vital to understand the conditions under which the ionomer is able to penetrate into primary pores inside agglomerates. Another challenge is to characterize the structure of the ionomer phase in the secondary void spaces between agglomerates and obtain the effective proton conductivity of the layer. 

---