Single-step Synthesis of CoAl Layered Double Hydroxides Electrode for Energy Conversion and Storage

• Main Authors: Chun Tsao, 曹均
• Other Authors: Chin-Jung Lin
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/az4was

碩士 === 國立宜蘭大學 === 環境工程學系碩士班 === 106 === In recent years, environmental protection consciousness gains ground, scientists were more focusing on energy storage and new green-energy development. Currently, they discovered that Layered Double Hydroxide (LDH) is a promising material. Owing to LDHs’ adjustable compositions, structures, and wide assembly, they can be tailored to fulfill specific demands for multiple applications in a variety of fields. Here we synthesized CoAl-LDH as an Oxygen Evolution Reaction (OER) catalyst and an electrode, which were studied and compared to their OER activities and electrochemical behaviors. In this study, the CoAl-LDHs nanosheet array on titanium foil was synthesized by a simple hydrothermal method and calcination treatment. Different from traditional method, we didn’t use any adhesion to stick the substrate and this method has been independent of substrate. We controlled different hydrothermal conditions (temperatures and times) to change the flake size and focused on the structures and its specific capacitances. In the hydrothermal method, we decided the best condition through their specific capacitance. After that, CoAl-LDH electrodes were named by CoAl-LDH-120-12-cz (c is an abbreviation of Calcination and z means the calcination temperature) in the calcination treatment. The thickness of CoAl-LDH-120-12-cz was measured by Scanning Electron Microscope (SEM), the results showed their dimension was about 3.67 μm. The structural characterization was carried out by X-ray Diffractometer (XRD) and lattice parameters, the samples presented a classic LDH structure. We inferred the porous borders were created by the gaps between the nanosheets from N2 Adsorption-Desorption Isotherm (BET) results. Their chemical compositions and valence electrons were analyzed through X-ray Photoelectron Spectrometer (XPS) and Temperature Programmed Reduction (TPR). In the electrochemical studies, the CoAl-LDH-120-12-c300 exhibited the highest specific capacitance of 68.57 F/cm3, the lowest charge transfer resistance and also long cyclic life (95% capacity retention after 100 cycles). In addition, the CoAl-LDH-120-12-c250 had excellent OER activity with an onset potential of 1.65 V vs. RHE and overpotential only of 424 mV to achieve a current density of 2 mA/cm2 and it was relatively stable. Moreover, we tried to synthesize CoAl-LDH film on different substrates (titanium, nickel, and conductive glass), confirmed the truth of the LDH growth wasn’t limited by substrates. As an electrode, the CoAl-LDH-120-12-c300 has a great cycling stability and specific capacitance; as an OER catalyst, the CoAl-LDH-120-12-c250 has an outstanding activity in alkaline medium. Lastly, the formula price of each electrode, it only cost 34.2 NTD during the non-summer period. Our CoAl-LDH holds excellent energy conversion and storage device potential as a promising capacitor as well as an OER catalyst with the advantages of great performance, simple preparation, no substrate restriction, eco-friendly and low cost.