Large area graphene – cobalt manganese oxide thin film for oxygen evolution reaction

• Main Authors: Chang-Ying Yang, 楊長穎
• Other Authors: Chun-hu Chen
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/14084524668459287138

碩士 === 國立中山大學 === 化學系研究所 === 104 === It is necessary to develop clean and green energy because of the shortage of non-renewable energy. The hydrogen and oxygen generated by water splitting is one of the solution for clean energy. However, energy required for water splitting is usually greater than energy generated by water splitting. Oxygen evolution reaction (OER) is the main reason of excessive energy consumption in the splitting process, thus it is necessary to prepare a catalyst to promote the OER. In this research, by a simple redox method with heating, we successfully synthesized cobalt manganese oxide hydroxide (CMOH) catalyst. This method is fast and simple; efficiently deposit catalytic thin film on large area substrate even on complex surfaces. At first, we used cobalt sulfate as precursor to prepare catalytic films (CMOH-sulfate, CMOH-S) for electrochemical measurement. However, the films (CMOH-acetate, CMOH-A) prepared by cobalt acetate have superior optical properties to CMOH-S, so we chose cobalt acetate for subsequent experiments. To further understand the difference between CMOH-S and CMOH-A, We characterized these two thin film by a series of characterization. The results of UV-visible and AFM show that the thickness of CMOH-A is smaller than CMOH-S thus has higher transmittance. CMOH-A have transmittance of 87.15% with thickness of 60 nm versus CMOH-S having 60.39% transmittance and 120 nm thickness. We further confirmed the thickness of CMOH-A to be 5 to 10 nm by TEM (rather than 60 nm by AFM), and the composition is amorphous. Despite the difference on optical property, CMOH-S and CMOH-A exhibit almost the same on OER activity. To study the reason, we altered the length of CMOH-A films, knowing that the active sites actually lie at the interface of catalyst and FTO glass. Finally, after covering a layer of graphene on the catalytic thin films and go through 500ºC calcination under Ar, we tremendously raise the stability of OER catalyzing process, with only 7.6% decay of current after 3000 circles scanning and still remain at same over potential (0.47 V at 10 mA cm-2).