S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Chemical and Biological Engineering (화학생물공학부) Theses (Ph.D. / Sc.D._화학생물공학부)
Design of bimetallic nanoparticles and its electrocatalysis for fuel oxidation
이원계 금속 나노입자의 설계 및 연료 산화에서의 전기촉매 작용
- 공과대학 화학생물공학부(에너지환경 화학융합기술전공)
- Issue Date
- 서울대학교 대학원
- fuel cell; electrocatalyst; ethanol oxidation reaction; bifunctional effect; electronic effect
- 학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부(에너지환경 화학융합기술전공), 2014. 2. 성영은.
- This study purposes the synthesis of nano-sized bimetallic electrocatalysts toward fuel oxidation reaction with the lower price and the enhanced activity compared to the existing catalysts. Moreover, a facile and rapid synthesis is introduced via a microwave-assisted synthesis instead of the conventional methods, and the complete oxidation reaction of fuel can be further achieved to improve the efficiency. The electrochemical and morphological properties of carbon supported platinum and tin oxide nanoparticles were evaluated in the first part, and the heterogeneous rhodium-tin alloyed nanoparticles deposited on the carbon as an electrocatalyst for the fuel oxidation were prepared to further reach to the complete oxidation reaction into the carbon dioxide as well as the better electrocatalytic activity and durability for fuel oxidation.
The electrocatalyst of carbon supported platinum and tin oxide nanoparticle was prepared through the microwave-assisted synthesis. It is clearly observed that the platinum nanoparticles and tin dioxide nanoparticles were uniformly dispersed onto the supporting material. The catalyst containing 16 wt% of tin oxide nanoparticles exhibited the highest activity and durability for the ethanol oxidation. The onset potentials of prepared electrocatalysts were negatively shifted compared to that of the commercial catalyst, result from the adsorbed CO species on platinum are more easily oxidized at lower potentials by hydroxyl groups adsorbed onto the surface of nearby tin oxide. In addition to the bifunctional effect, it is confirmed that the electronic effect was also acted in the platinum-tin oxide nanocomposites. As the amounts of tin oxide increased, the white line of Pt L3-edge decreased. According to the cyclic voltammetry results and theoretical calculations, the excess amounts of tin oxide nanoparticles dispersed on the carbon surface play a role as an isolating barrier that hinders the electron transfer between platinum and carbon support, while too low amounts of tin oxide nanoparticles limit the transfer of adsorbed hydroxyl groups for the oxidation of carbon monoxide species.
Without platinum as one of the most valuable metal, the rhodium-tin alloy nanoparticle was formed for the efficient electrocatalyst toward fuel oxidation. The alloyed bimetallic nanoparticles were uniformly distributed onto the whole surface of carbon supporting material through the microwave-assisted method. Electrocatalytic activity and the ratios of peak current density at forward scan and backward scan were significantly enhanced in the tin-abundant sample. Moreover, the rhodium-tin electrocatalysts produced much carbon dioxide compared to the platinum-based conventional catalyst, result from the accomplishment of additional total oxidation of ethanol including the C-C bond splitting. Not only the increased production of carbon dioxide but also the negative shift in onset potentials was observed. As the tin ratios were increased, the white lines of Rh K-edge were up-shifted that the interactions between rhodium and adsorbed species become stronger than the pure metallic rhodium. It indicates the electronic modifications can be powerful strategy to fulfill both the increased performance and the lower expense. Even in concentrated fuel solutions and at lower operating potentials, the superior activity and durability were maintained. These results correlated with the lower overpotentials and the increased reaction rates under various fuel concentrations, confirmed from the Tafel plots and Butler-Volmer equations.
Consequently, the bimetallic nanoparticles with improved electrocatalytic activity and durability toward fuel oxidation were successfully synthesized through the facile and swift method.