| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 95 === Catalytic activity of Ti-Cu and Ti-Co films for oxygen reduction reaction (ORR) in the 0.5M H2SO4 was investigated in this work. Ti-Cu and Ti-Co films in variant compositions were prepared with magnetron sputtering method. Electrochemical technologies such as slow scan voltammetry (SSV), Tafel-Plot (TP), cyclic voltammetry (CV), and rotating disk eelectrode (RDE) were employed to study the electrochemical behavior of the films. Energy dispersive spectrometry (EDS) and x-ray photoelectron spectrometer (XPS) were applied to analyze the composition of the films before and after electrochemical testing.
The results of SSV indicated that both Ti-Cu and Ti-Co films were catalytically active for ORR. Ti-Co films were more active than Ti-Cu. The catalytic activity increases with increasing the concentration of Co (from 40-60 at%) in Ti-Co films and that of Cu (from 50 to 90 at%) in Ti-Cu. With higher catalytic activity, Ti-Co film revealed higher onset potential (i.e., at 1.0 V) than Ti-Cu (i.e., 0.6~0.7V). At a constant potential of 0.2V, a film of Ti50Co50 indicated a greater reduction current density (272.14μA/cm2) than Ti50-Cu50 (i.e., 28.57μA/cm2).
Resulting from CV, there was a strong broad oxidation peak at 0.5V on the first scan cycle of the Ti-Cu films. This peak disappeared on the second cycle and a week small one present at lower potential (i.e., 0.3 V) instead of it. The strong broad peak is ascribed the oxidation of Cu to Cu+ and Cu2+ and the weak small one to only oxidation of Cu to Cu+. The cyclic voltammogram depicted that Ti-Co films revealed only a symmetrical and smooth loop in the potential range from 0 to 1.2V. No any peak was present on the loop. This phenomenon implied that Ti-Co was more stable than Ti-Cu. The instability of Ti-Cu film was due to dissolution of Cu in 0.5M H2SO4. .Using the RDE data and Koutecky-Levich equation, the number of electron transferred in the ORR process was estimated. Almost four electrons were transferred on the Ti-Cu and about three electrons were transferred on the Ti-Co films.
Tafel plot provided the evaluation of exchange current density for ORR. The exchange current density (μA/cm2) decreases in the order Co (1.26 x 10-8) > Cu (8.54 x 10-9) > Ti (1.21 x 10-10).
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