Hybrid Core–Shell Microparticles Based on Vaterite Polymorphs Assembled via Freezing-Induced Loading

The hybrid core–shell system was fabricated based on pre-synthesized vaterite microparticles and iron oxide nanoparticles applying two technical approaches: physical adsorption of the nanoparticles from a suspension at room temperature and a newly developed method of freezing-induced loading. A combination of transmission electron microscopy and X-ray diffraction paired with precision nanomanipulation allows us to analyze the inner structure of the hybrid system, indicating that both vaterite and calcite phases were covered by Fe3O4 shells. The freezing-induced loading was found to be more preferable due to the formation of the core–shell nanoparticles in a more stable polymorphic composition of calcium carbonate when compared to physical adsorption

Influence of the Polymer Precursor Structure on the Porosity of Carbon Nanofibers: Application as Electrode in High-Temperature Proton Exchange Membrane Fuel Cells

Polyacrylonitrile and polyheteroarylenes, such as polybenzimidazole (PBI) and a polymer of intrinsic microporosity (PIM-1), have been employed to prepare nanoporous electrospun carbon nanofiber (CNF)-based materials for high-temperature proton-exchange (or polymer-electrolyte) membrane (HT-PEM) fuel cells. The nanoporous CNF mats are obtained by Nanospider (needle-free) electrospinning method from polymer solution followed by pyrolysis at 1500 °C to form nanoporous electrospun polymer nanofiber self-supporting mats with micropores (D D 2–50 nm). The nanoporous CNF samples are extensively characterized by N2 and CO2 adsorption applying the BET, BJH, Dubinin–Radushkevich (DR), NLDFT, and GCMC methods, CO2 uptake, Raman spectroscopy, elemental analysis, electrical conductivity, electron microscopy, and XPS. The role of the polymer precursor on the obtained values of specific surface area (SSA) and volume for micro- and mesopores is presented and discussed. The PBI-based CNF material reaches a micropore SSA of 919 m2 g–1 and CO2 uptake of 4.0 mmol g–1 derived from CO2 adsorption (273 K) data, and a micropore SSA of 873 m2 g–1 according to the t-method derived from N2 adsorption data. Close values confirm higher accessibility of micropores compared with the case of PIM-based CNF, where the micropore SSA values derived from CO2 and N2 adsorption data are different and indicate the partial inaccessibility of micropores for low-temperature nitrogen adsorption (77 K). Platinum-decorated CNF mats are successfully tested as electrodes for HT-PEM fuel cells, showing the feasibility of using the mats as cathodes; nevertheless, further optimization is required. For CNF anodes, the HT-PEM fuel cell performance reaches 0.69 V at 0.2 A cm–2 and 0.53 W cm–2 at 1.4 A cm–2 which permits the use of the Pt/CNF mats as anodes