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.
Highlights
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]
Amorphous Ti-15 at.% Ni-15 at.% Si alloys prepared by the rotating wheel method were leached out for 288 ks in 1 N HCl solution at room temperature and anodically oxized for 3.6 ks in 0.5 M H2SO4 solution at 50 V and 278 K, respectively
atomic force microscope (AFM) images showed a large numbers of volcanic craters with round pores approximately 70 nm in diameter on amorphous TiO2-x surface
Summary
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]. 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. We report DC and AC charging/discharging characteristics for anodic oxidized-amorphous Ti15 at.% Ni-15 at.% Si alloy supercapacitors with higher narrow cavity densities and higher electric resistivities, with an aim to obtain further wide behaviors for Ti-Ni-Si ones, in comparison with those of the de-alloyed Si-Al alloy one [10,11]. Capacitances were calculated as a function of frequency between 1 mHz and 1 MHz from AC electric charge/discharge pulse curves of 10 V applied at 25 ns ~ 0.1 s intervals, using a mixed-signal oscilloscope (MSO 5104, Tektronix, Beaverton, OR, USA) and 30 MHz multifunction generator Experimental inspection for electric storage was carried out by swing of reflected light of DC Galvanometer (G-3A, Yokogawa Electric, Tokyo, Japan) after charging at 1 mA for 20 s
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