|The power performance of the SWNH/SWNT composite electrode surpasses other nanocarbon electrodes. Credit: ACS, Click to enlarge.|
Researchers at Japan’s National Institute of Advanced Industrial Science and Technology (AIST) and Japan Science and Technology Agency (JST) have developed a novel high-power composite material for supercapacitor electrodes.
The material, featuring a unique meso-macro pore structure engineered through the utilization of single-walled carbon nanotubes (20 wt%) as scaffolding for single-walled carbon nanohorns (80 wt%), offers a high maximum power rating of 990 kW/kg and 396 kW/L. A paper on their work was published in the journal ACS Nano.
The single-walled nanohorn/single-walled nanotube (SWNH/SWNT) composite electrode also exhibited durable operation (6.5% decline in capacitance over 100,000 cycles) as a result of its monolithic chemical composition and mechanical stability, the team found.
Compared with another high-power electrode made from single-walled carbon nanotubes, the composite electrode had a lower surface area (280 vs 470 m2/g from nitrogen adsorption), and a higher meso-macro pore volume (2.6 vs 1.6 mL/g from mercury porosimetry). This enabled the composite electrode to retain more electrolyte, ensuring facile ion transport, and hence achieving a higher maximum power rating.
The maximum power rating of the SWNH/SWNT composite electrode (990 kW/kg) was almost twenty times higher than the estimated maximum power performance (~50 kW/kg) of the only previous report on SWNH electrodes, and more than twice that of the SWNT Bucky paper (400 kW/kg) examined here. Comparison of the performance of the composite electrodes with other nanocarbon electrodes showed that while the composite electrodes have been operated only at 2.5 V, their maximum power rating still surpassed other nanocarbon electrodes.
The only electrode (nanocarbon based or otherwise) reported having a higher maximum power (3.2 MW/kg, 16 kW/l vs 0.99 MW/kg, 396 kW/l for the composite electrodes) was composed of a sparse MWNT forest electrode (density of 0.005 g/cm3). Sparse CNT forest electrodes naturally have higher power performance as essentially individual CNTs within the forest are immersed in an almost infinite sea of electrolyte, i.e., infinite supply of ions. Here, our composite material has achieved a similar power performance, by tailoring the pore structure to optimize electrolyte retention yet having a density eighty times that of the sparse CNT forest.—Izadi-Najafabadi et al.
Ali Izadi-Najafabadi, Takeo Yamada, Don. N. Futaba, Masako Yudasaka, Hideyuki Takagi, Hiroaki Hatori, Sumio Iijima, Kenji Hata (2011) High-Power Supercapacitor Electrodes from Single-Walled Carbon Nanohorn/Nanotube Composite. ACS Nano Article ASAP doi: 10.1021/nn1017457