Non-noble-metal biochars derived from biowastes for oxygen reduction reaction in fuel cell

• Main Authors: Hung-ChihKuo, 郭泓志
• Other Authors: Shou-Heng Liu
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/mr6a78

碩士 === 國立成功大學 === 環境工程學系 === 107 === Fuel cell is a device converting the chemical energy into electricity through an electrochemical reaction. At the cathode, the hydrogen ions, electrons, and oxygen are reacted and produced water. Compared to fossil fuels, the fuel cell only produce electricity and water without the emission of pollutants, so the fuel cell meets the concepts of environmental friendliness and clean energy. However, the sluggish kinetics of the cathodic oxygen reduction reaction and the high cost, poor durability of noble metal catalysts limit the large-scale commercial applications. In this study, we recover lignocellulose biomass to synthesize non-noble metal catalysts, and choose transition metal and potassium hydroxide as catalysts and activation agents, respectively. The samples after carbonization are activated by 800 W microwave radiation for 10 min. The obtained biochars are washed with 0.5 M HCl to remove K ions. For nitrogen doping, a post-treatment is performed by using microwave radiation with 800 W under NH3 atmosphere. By microwave irradiation, we produced core-shell structured M-N-C catalysts. Compared with lignin, cellulose-derived catalysts display superior ORR catalytic activity (Eonset=-0.05 V) due to more Fe-Nx active sites and mesopore structure which can promote mass transport. Moreover, FeCo alloys with ratio (Fe:Co = 1:1) samples not only show a comparable activity but also exhibit a better stability and maintain 73% of current density after 10000s of operation. In terms of biomass waste (sugarcane), the catalysts synthesized by Fe/Co (1:1) encapsulated with N doped carbon layers show a type IV adsorption-desorption isotherm, indicating the existence of mesopores. The formation of core-shell structure of FeCo alloys can be observed as evidenced by TEM. Meanwhile, the SC-Fe5Co5 exhibits excellent ORR catalytic activity (Eonset up to −0.06 V) through four-electron pathways (n≒3.9) in the alkaline electrolyte and excellent resistance to methanol crossover. Moreover, the synthesis process via a microwave-assisted treatment could provide a facile and energy-effective route to construct core-shell structured metal-N-C.