고분자 전해질 연료전지의 장시간 운전 안정성 향상을 위한 백금 담지 실리카 촉매의 제조에 관한 연구

Abstract

Synthesis of platinum (Pt) nano-sized catalyst dispersed on various form of silica (SiO2) support was investigated using chemical processes including alcohol reducing method and modified Stö ber method, and application for proton exchange membrane fuel cell (PEMFC) system was conducted. Pt catalysts immobilized support materials should satisfy several requirements, e.g. high surface area, high electric conductivity, chemical stability and thermal stability. Especially, in PEMFC operation, support materials must bear highly acidic condition in pH range from 2 to 3, to avoid support degradation as well as catalyst loss. As a support material, SiO2 have advantages, such as simple fabrication, good stability in acidic condition and excellent thermal stability. Therefore, in this study, SiO2 were employed as support material on basis of the advantages mentioned above, although they have extremely low conductivity. For the fabrication of Pt immobilized on SiO2 support with high durability, preparation of Pt catalysts in two different types of SiO2 supports, e.g. Pt immobilized spherical SiO2(Pt-SiO2) and PS@SiO2 core-shell sphere (Pt-PS@SiO2) have been conducted by a novel route involving chemical reduction of Pt ions. After that, prepared catalyst materials were employed in PEMFC catalyst layer by fabrication of MEA using conventional Pt-carbon black (Pt-CB) and two type of SiO2-supported Pt catalyst. Fabrication of thin membrane-electrode assembly (MEA) with catalyst layer (CL) thickness of 15~20 μm was conducted by the decal transfer method (DTM). Pt-SiO2 catalysts of various diameters of SiO2 support in range from 100 nm to 600 nm have been fabricated and the above procedures were repeated to evaluate the effect of support size on cell performance. Cell performance of MEA prepared by two different catalysts is investigated in details. Pt-PS@SiO2 core-shell MEA has achieved similar degree of cell polarization as conventional Pt-CB MEA, while Pt-SiO2 MEA has presented degraded cell polarization on basis of electrode over-voltage. In comparison with cell performances from the literatures, presented MEA in this work indicated the most enhanced performance among the MEAs with SiO2 supported Pt catalysts.