Structural and Electrochemical Properties of Physically and Chemically Activated Carbon Nanoparticles for Supercapacitors

The demand for supercapacitors has been high during the integration of renewable energy devices into the electrical grid. Although activated carbon materials have been widely utilized as supercapacitor electrodes, the need for economic and sustainable processes to extract and activate carbon nanomaterials is still crucial. In this work, the biomass waste of date palm fronds is converted to a hierarchical porous nanostructure of activated carbon using simple ball-milling and sonication methods. Chemical and physical activation agents of NaOH and CO2, receptively, were applied on two samples separately. Compared with the specific surface area of 603.5 m²/g for the CO2-activated carbon, the NaOH-activated carbon shows a higher specific surface area of 1011 m2/g with a finer nanostructure. Their structural and electrochemical properties are functionalized to enhance electrode–electrolyte contact, ion diffusion, charge accumulation, and redox reactions. Consequently, when used as electrodes in an H2SO4 electrolyte for supercapacitors, the NaOH-activated carbon exhibits an almost two-fold higher specific capacitance (125.9 vs. 56.8 F/g) than that of the CO2-activated carbon at the same current density of 1 A/g. Moreover, using carbon cloth as a current collector provides mechanical flexibility to our electrodes. Our practical approach produces cost-effective, eco-friendly, and flexible activated carbon electrodes with a hierarchical porous nanostructure for supercapacitor applications.

Cyanogel-Derived Synthesis of Porous PdFe Nanohydrangeas as Electrocatalysts for Oxygen Reduction Reaction

It is important to develop cost-efficient electrocatalysts used in the oxygen reduction reaction (ORR) for widespread applications in fuel cells. Palladium (Pd) is a promising catalyst, due to its more abundant reserves and lower price than platinum (Pt), and doping an earth-abundant 3d-transition metal M into Pd to form Pd–M bimetallic alloys may not only further reduce the use of expensive Pd but also promote the electrocatalytic performance of ORR, owing to the synergistic effect between Pd and M. Here we report a cyanogel-derived synthesis of PdFe alloys with porous nanostructure via a simple coinstantaneous reduction reaction by using K2PdIICl4/K4FeII(CN)6 cyanogel as precursor. The synthesized PdFe alloys possess hydrangea-like morphology and porous nanostructure, which are beneficial to the electrochemical performance in ORR. The onset potential of the porous PdFe nanohydrangeas is determined to be 0.988 V, which is much more positive than that of commercial Pt/C catalyst (0.976 V) and Pd black catalyst (0.964 V). Resulting from the unique structural advantages and synergetic effect between bimetals, the synthesized PdFe nanohydrangeas with porous structure have outstanding electrocatalytic activity and stability for ORR, compared with the commercial Pd black and Pt/C.

The model of potential barrier appearing in a hydrolayer localized in a two-layer porous nanostructure

A model has been proposed to describe the potential barrier that appears during interaction of two compacted layers consisting of hydrophilic oxide nanoparticles of different sizes in each layer upon saturation of this structure with adsorbed water. The dependence of the space charge density of the compacted powder material on the density of particles in it has been theoretically calculated. The distribution of the potential over the thickness of contact between two layers consisting of nanoparticles with different sizes has been obtained.

ZnCDs/ZnO@ZIF-8 Zeolite Composites for the Photocatalytic Degradation of Tetracycline

Considering the photocatalytic performance of CDs, ZnO, and the unique porous nanostructure and stability of ZIF-8, we prepared ZnCDs/ZnO@ZIF-8 zeolite composites. The resultant material represented an enhanced ability for the photodegradation of TC compared with that of ZnCDs and ZnO. The photocatalytic degradation efficiency reached over 85%. The catalytic activity of the composites was maintained after four cycles. The experimental result indicated that ×O2 radical was the active species in the reaction.