RESUMEN
Nanoporous carbon was synthesized from microalgae as a promising electrode material for electric double layer capacitors due to its large specific surface area and controllable pore structures. The pore textural properties of the algae-derived-carbon (ADC) samples were measured by N2 adsorption and desorption at 77 K. The performance of the activated carbon (AC) as supercapacitor electrodes was determined by the cyclic voltammetry and galvanostatic charge/discharge tests. The effect of the nanoporous carbon structure on capacitance was demonstrated by calculating the contributions of micropores and mesopores toward capacitance. Capacitance was significantly affected by both pore size and pore depth. To further increase the specific capacity, a single-pot synthesis of porous carbon supported CoO composite (CoO/ADC) electrode material was developed using microalgae as the carbon source and Co(OH)2 as both a carbon activation agent and CoO precursor. After carbonization, CoO particles were formed and embedded in the ADC matrix. The synergic contributions from the combined CoO and ADC resulted in better supercapacitor performance as compared to that of the pure CoO electrode. The calculated specific capacities of CoO/ADC were 387 and 189 C g-1 at 0.2 and 5 A g-1, respectively, which were far more than the capacities of pure CoO electrode (185 C g-1 at 0.2 A g-1 and 77 C g-1 at 5 A g-1). The cycle stability of CoO/ADC also increased significantly (83% retention of the initial capacity for CoO/ADC vs 63% for pure CoO). This research had developed a viable and promising solution for producing composite electrodes in a large quantity for commercial application.
RESUMEN
Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb2O5 NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb2O5 NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb2O5 NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb2O5 NCs existed. The architecture of ultrafine Nb2O5 NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied by Nb(5+)/Nb(4+) redox reaction and the ultrafine Nb2O5 NCs provide more surface area to accomplish the redox reaction.
