Fundamental Mechanisms of Platinum Catalyst for Oxygen Reduction Reaction in Fuel Cell: Density Functional Theory Approach

Kang, Seok Ho; Lee, Chang-Mi; Lim, Dong-Hee; Kang, Seok Ho; Lee, Chang-Mi; Lim, Dong-Hee

doi:2016.38.5.242

The Korean text of this paper can be translated into multiple languages on the website of http://jksee.or.kr through Google Translator.

J Korean Soc Environ Eng > Volume 38(5); 2016 > Article

Original Paper

J Korean Soc Environ Eng 2016;38(5): 242-248. doi: https://doi.org/10.4491/KSEE.2016.38.5.242

연료전지 산소환원반응 향상 위한 백금 촉매의 구조적 특성: 밀도범함수이론 연구

강석호, 이창미, 임동희

충북대학교 환경공학과

Fundamental Mechanisms of Platinum Catalyst for Oxygen Reduction Reaction in Fuel Cell: Density Functional Theory Approach

Seok Ho Kang, Chang-Mi Lee, Dong-Hee Lim

Department of Environmental Engineering, Chungbuk National University

Corresponding author

Dong-Hee Lim ,Tel: 043-261-2467 , Fax: 043-264-2465, Email: limkr@cbnu.ac.kr

Received: January 26, 2016; Revised: March 14, 2016; Accepted: April 4, 2016. Published online: May 31, 2016.

ABSTRACT

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt (3.977 Å) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

Key Words: Fuel Cell, Oxygen Reduction Reaction (ORR), Platinum (Pt) Catalysts, Density Functional Theory (DFT)