Electric charging/discharging characteristics of super capacitor, using de-alloying and anodic oxidized Ti-Ni-Si amorpho
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NANO EXPRESS
Open Access
Electric charging/discharging characteristics of super capacitor, using de-alloying and anodic oxidized Ti-Ni-Si amorphous alloy ribbons Mikio Fukuhara1,2,3* and Kazuyuki Sugawara4
Abstract Charging/discharging behaviors of de-alloyed and anodic oxidized Ti-Ni-Si amorphous alloy ribbons were measured as a function of current between 10 pA and 100 mA, using galvanostatic charge/discharging method. In sharp contrast to conventional electric double layer capacitor (EDLC), discharging behaviors for voltage under constant currents of 1, 10 and 100 mA after 1.8 ks charging at 100 mA show parabolic decrease, demonstrating direct electric storage without solvents. The supercapacitors, devices that store electric charge on their amorphous TiO2-x surfaces that contain many 70-nm sized cavities, show the Ragone plot which locates at lower energy density region near the 2nd cells, and RC constant of 800 s (at 1 mHz), which is 157,000 times larger than that (5 ms) in EDLC. Keywords: Electric storage devices; Amorphous alloys with TiO2-x surfaces; Nanometer sized cavity
Introduction Titanium oxide (TiO2) is of considerable interest for wide range of applications, including photocatalysis [1], optovoltaics [2], solar energy conversion [3], chemical sensors [4], bioprobes [5] and environmental pollution control [6]. Although the majority of the applications of TiO2 are generally controlled by the crystalline phase [7], we report distinguished amorphous material supercapacitors, devices that store electric charge on their amorphous titanium oxide surfaces that contain many 70-nm sized cavities. Following the capacitance studies of Ni-Nb-Zr-H glassy alloys with femtofarad capacitance tunnels [8,9], we have found that the capacitance of nanocrystalline de-alloyed Si-Al [10,11] or Si-Al-V [12], and de-alloyed and anodic oxidised amorphous Ti-Ni-Si alloy ribbons [13] show prompt charging/discharging of 102 μF (0.55 F/cm3) at a frequency of 1 mHz, from 193 to 453 K, and with a high voltage variation from 10 to 150 V. Especially, the de-alloyed and anodic oxidized Ti-Ni-Si alloy one displayed a capacitance of ~ 4.8 F (~52 kF/cm3) in discharging * Correspondence: [email protected] 1 New Industry Creation Hatchery Center, Tohoku University, 3-4-1, Sakuragi, Tagajyo, Miyagi 985-8589, Japan 2 Fracture and Reliability Research Institute, Tohoku University, Sendai 980-8579, Japan Full list of author information is available at the end of the article
behaviors for voltage after 1.8 ks charging at DC current of 100 mA [13]. We assume that the surface structure of the oxide consists of a distributed constant equivalent circuit of resistance and capacitance, analogous to active carbons in electric double-layer capacitors (EDLCs). The amorphous materials of interest are completely different from the conventional “wet” cells such as EDLC and secondary cells which are controlled by diffusivity of ions. We termed this device a “dry” electric distributed constant capacitor (EDCC). In this study, we report DC and AC ch
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