Paulo J. Ferreira

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Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a(More)
Zinc Oxide (ZnO) nano-superstructures (NSSs) have attracted intense research interests due to their large surface areas and unique properties. In this work, we report an original approach to synthesize ZnO NSSs in a one-step manner with a hydrothermal method. The crystalline structures and growth mechanism can be understood by surface energy calculations.(More)
An inverse Hall–Petch effect has been observed for nanocrystalline materials by a large number of researchers. This effect implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation-based models, diffusion-based models, grain-boundary-shearing models and(More)
The current success of nanocrystalline materials is due to their unusual and promising properties compared to coarser grain size materials. However, maintaining the nanocrystalline character during processes or applications is not an easy task, due to the tendency towards grain growth exhibited by nanocrystalline materials. It is well known that the(More)
Atomically resolved structures and compositions of Pt alloy nanoparticles were obtained using aberration-corrected high-angle dark field imaging, which was correlated to specific ORR activity based on a Pt surface area. The enhanced specific ORR activity (approximately 2 times relative to Pt) of acid-treated "Pt3Co" nanoparticles can be related to(More)
Rotating disk electrode measurements of acid-treated “Pt3Co” nanoparticles showed specific oxygen reduction reaction (ORR) activity (∼0.7 mA/cmPt at 0.9 V vs RHE in 0.1 M HClO4 at room temperature), twice that of Pt nanoparticles. Upon annealing at 1000 K in vacuum, the ORR activity at 0.9 V was increased to ∼1.4 mA/cmPt (four times that of Pt(More)
Certain signal reconstruction problems can be understood in terms of frames and redundant representations. The redundancy is useful because it leads to robust signal representations, that is, representations in which partial loss of data can be tolerated without misbehavior or adverse effects. This chapter begins by presenting a few engineering problems in(More)
Nanocrystalline metals demonstrate a range of fascinating properties, including high levels of mechanical strength. However, as these materials are exposed to high temperatures, it is critical to determine the grain size evolution, as this process can drastically change the mechanical properties. In this work, nanocrystalline sputtered Cu thin films with 43(More)