Adsorption of CO2 at 273 K up to 4 MPa has been studied in activated carbons and carbon molecular sieves of different origins and pore size distribution. The materials selected for this study include carbon molecular sieves with a pore size (i.e., pore width) between 0.3 and 0.5 nm, activated carbons with supermicroporosity (pore size between 0.7 and 2 nm), and mesoporous and macroporous activated carbons. The relative fugacities covered in the experiments ranges from 10 -4 to nearly 1. Additionally, N2 adsorption at 77 K at subatmospheric pressures has been also done. The experimental conditions used allow us to compare both measurements at similar adsorption potentials, in which both gases adsorb in the different ranges of porosity. The results obtained show that CO2 adsorbs at 273 K in the different ranges of porosity following a mechanism similar to that of N2 at 77 K. CO2 is sensitive to narrow micropores not accessible to N2 at 77 K, and hence, it is an adequate complement to N2 at 77 K. This is especially important for the characterization of the narrow micropores of carbonaceous solids and, especially, carbon molecular sieves. CO2 adsorbs in mesopores according to the capillary condensation mechanism.

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The adsorption of CO2 up to pressures of 4 MPa has been studied using two series of activated carbon fibers (ACFs) covering a wide range of burn-off. The relative fugacities covered in these experiments range from 3 × 10-4 to 0.76. Additionally, N2 adsorption at 77 K and CO2 adsorption at 273 and 298 K at subatmospheric pressures have been carried out. The experiments performed at high pressures allow us to compare both adsorptives at similar ranges of adsorption potential. The results obtained led to the following conclusions:  (i) CO2 adsorption at 273 K at subatmospheric pressures is a suitable technique to characterize the narrow microporosity of the ACF. (ii) The use of N2 to characterize the narrow microporosity is not appropriate because its adsorption is limited by the existence of diffusional restrictions in this type of porosity. (iii) CO2 at 273 K (or 298 K) is an adsorptive that behaves quite similarly to N2 at 77 K at comparable relative pressure ranges; thus, CO2 adsorbs in the super-microporosity range (pore size:  0.7−2 nm) at 298 K if pressures of about 4 MPa are used.

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Hydrogen storage has been studied in a large variety of activated carbons and activated carbon fibers and a wide range of pressures (up to 70 MPa). The experimental technique used has good reliability, and the experiments performed have a small error and high reproducibility. This seems to be essential to get trustworthy conclusions. In these samples, we have not found large amounts of hydrogen adsorbed. In any case, an activated carbon derived through a simple preparation method provides hydrogen storage values at 10 MPa close to 1 wt % (i.e., a value close to the target from an application point of view). The experimental results have been compared with theoretical work found in the literature, and an important agreement can be observed. From this study, we conclude that the optimum pore size for hydrogen storage is that which can hold two layers of adsorbed hydrogen. This work also considers practical aspects related to hydrogen storage in activated carbons and activated carbon fibers.