Chia-Chin Chang

Kinetics of oxygen reduction at oxide-derived Pd electrodes in alkaline solution

Oxygen reduction at oxide-derived Pd electrodes is investigated by using the rotating disc electrode technique. On the basis of these experiments along with further data analysis (ie reaction orders, Tafel slopes, etc.), a mechanism of oxygen reduction on an oxide-derived Pd electrode is proposed to explain the observed rate equation.

An investigation of thermally prepared electrodes for oxygen reduction in alkaline solution

The electrocatalytic activity and stability of various thermally prepared electrodes (of metal species Pd, Pt, Ir, Co, Ru, and Ni) for oxygen reduction in 1 M KOH are investigated. Electrocatalytic activity is elucidated by potentiostatic polarization and galvanostatic electrolysis. Tafel slopes, exchange current densities and onset potentials are derived from potentiostatic polarization and are used to explain the different processes of oxygen reduction on various electrodes. In order to evaluate electrode stability, CV, SEM and XRD are used to test for changes in electrode surface.

Effects of Dispersant on the Conductive Carbon for LiFePO4 Cathode

Carbon-based electrically conductive particles (cECP) are commonly used to reduce interparticle resistance in Li-ion batteries, but cECP tend to flocculate in the dense slurries used to fabricate electrodes. Herein, a novel dispersant limits flocculated cECP particle size and improves cECP dispersion. The increased cECP efficacy allows reduced addition of carbon to the battery, thereby increasing the ratio of active material to conductive material and increasing volumetric energy density. With/without dispersant LiFePO 4 /ketjenblack cathodes are examined by scanning electron microscopy (SEM), slurry viscosity, electrochemical redox behavior, electrochemical impendence spectroscopy (EIS) and charge/discharge cycling performance. Discharge capacity, durability and resistance are better for the with-dispersant LiFePO 4 cathode. EIS shows reduced interfacial impedance and increased cycling performance for the with-dispersant electrode. SEM shows smooth distribution of nano-scale particles of consistent size with dispersant use. Without dispersant, the cECP particles are micro-scale, with high variability in size and location. It is seen that a good cECP dispersant in the initial electrode slurry improves Li-ion battery performance, primarily because of a more cohesive cECP network between the active material particles.

A mixture design approach to thermally prepared Ir–Pt–Au ternary electrodes for oxygen reduction in alkaline solution

Thermally prepared ternary Ir–Pt–Au electrodes were investigated experimentally over their entire compositional range using the mixture design method. The results, involving voltammetric charges from electrode redox (q*), oxygen reduction current densities (i), and their correspondingly electrocatalytic activities (i/q*), are examined through regression models and response surface contour plots. Using mixture experimental design, the empirical models are fitted and plotted as contour diagrams which facilitate comparisons with experimental trends noted by other investigators and reveal the synergistic/antagonistic effects between the mixed oxides. The material characterization was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to assist in interpreting the electrocatalytic activity for oxygen reduction.

Tris(pentafluorophenyl)borane as an Electrolyte Additive to Improve the High Temperature Cycling Performance of LiFePO4 Cathode

The capacity fading of LiFeP0O 4 batteries using 1.2 mol dm -3 LiPF 6 ethylene carbonate/dimethyl carbonate electrolyte with tris(pentafluorophenyl)borane (TPFPB) additive at 60°C is investigated by cyclic voltammetry, cyclability, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The cyclability results show that the LiFePO 4 -Li cell with the TPFPB additive electrolytes exhibits high discharge capacity and good cycling performance at 60°C. The LiFePO 4 electrode cycled at 60°C without the TPFPB additive shows a significant increase in charge-transfer resistance by EIS analysis. The TPFPB additive in the electrolyte reduces the difference in the charge-transfer resistance before and after 100 cycles at elevated temperatures. SEM results show that after 100 cycles at 60°C in an electrolyte without TPFPB additive, the LiFePO 4 electrode forms a visible material on the electrode surface. The observed material is presumably related with capacity fading in the LiFePO 4 ―Li cell. The results indicate that TPFPB in the electrolyte prevents the formation of the observed material on the electrode, reduces charge-transfer resistance, and enhances cycling performance of the LiFePO 4 ―Li cells at 60°C.

Lithiation-induced crystal restructuring of hydrothermally prepared Sn/TiO2 nanocrystallite with substantially enhanced capacity and cycling performance for lithium-ion battery

A Sn-doped TiO2 nanocrystallite with the composition of Sn0.1Ti0.9O2 was prepared by hydrothermal co-precipitation followed by thermal annealing at 600 °C for 2 hours. Results combining high-resolution transmission electron microscopy, in situ XRD, ex situ XAS, and electrochemical impedance spectroscopy indicate that Sn0.1Ti0.9O2 underwent restructuring to give Sn-substituted TiO2 (Sn to Ti sites) by a lithiation reaction at 0.1C in a lithium-ion battery. The capacity and cyclability of Sn0.1Ti0.9O2 were increased by ∼73% (to ∼598 mA h g−1) and ∼17.4% compared with those of TiO2 (∼345 mA h g−1 and ∼22%) at 0.1C until the 250th cycle. Our results proved that these improvements were caused by the self-aligned formation of Sn–Ti oxide and the subsequent formation of a SnLix local alloy at Ti sites.