Clay–Carbon Nanotubes Hybrid Materials for Nanocomposite Membranes: Advantages of Branched Structure for Proton Transport under Low Humidity Conditions in PEMFCs

A new class of hybrid materials based on carbon nanotubes (CNT) rooted on smectite clays (SWy) was synthesized by catalytic chemical vapor deposition (CCVD) method, and studied to be introduced in a perfluorosulfonic acid (Nafion) membrane. Side-wall chemical oxidation and organo-functionalization of the CNT was performed using organic ester molecules containing hydrophilic groups (−RSO₃H). SWy–CNT nanoadditives were incorporated in the polymer by solution-precipitation method producing highly homogeneous nanocomposite membranes with outstanding mechanical properties. Materials were characterized by a combination of techniques (TGA, Raman, FT-IR, SEM, TEM, and DMA), while a deep investigation on the water transport properties was performed by NMR methods (PFG and relaxation times). Membranes containing SWy–oxCNT–RSO₃H nanoadditives are able to guarantee a very high proton diffusion in “quasi-anhydrous” conditions. Proton mobility is ensured by a correct network created from the long nanotubes (well distributed through the clay nanoplatelets) appropriately functionalized with acid groups. Remarkable are the electrochemical results: the best membrane reaches conductivities of 7 × 10^–2 S cm^–1 at 120 °C and 30% RH, 1 order of magnitude higher than pristine polymer, and a rather high value in the current panorama of the PEMFCs

Cu-BTC/Aminated Graphite Oxide Composites As High-Efficiency CO₂ Capture Media

CO₂ adsorption isotherms on Cu-BTC/aminated graphite oxide composites were measured in the pressure range up to 1.5 MPa at three different temperatures close to ambient. Adsorption capacity, isosteric heat of adsorption, and regenerability were investigated. They are considered as significant factors determining the practical application of materials for CO₂ capture. The results indicate a significant improvement in the performance of the composites as CO₂ adsorbents in comparison with the parent Cu-BTC MOF. Among all samples analyzed, the composite of Cu-BTC and modified graphite oxide with the highest N content (MOF/GO-U3) is the best performing sample. On its surface 13.41 mmol/g CO₂ was adsorbed at room temperature and 1.5 MPa. A high selectivity for CO₂ adsorption over that of CH₄ was found. The selectivities for CO₂ adsorption over N₂ are governed by the properties of the MOF phase. A relatively low heat of CO₂ adsorption and the high degree of surface homogeneity cause that the composites can be fully regenerated and used in multicycle adsorption with the minimum energy demand