Platinum Thin Catalyst Layer for Proton Exchange Membrane Fuel Cell

Abstract

As one of the renewable energy, polymer electrolyte membrane fuel cell (PEMFC) is a promising candidate because of its good performance efficiency and environment-friendly technique. However, high cost and poor durability of Pt catalys are main obstacles to a commercialization of PEMFC. As a solution for the problems, some researchers have focused on thin film catalyst layer instead of Pt/C catalyst for reducing the amount of platinum use and for enhancing performance at high current density. For example, NSTF (nanostructured thin film) catalyst layer and inverse opal structured catalyst layer were studied for improving mass-transfer and enhancing durability and stability of catalyst.[1-2] In this study, we used ultrasound to form a thin catalyst layer. By using ultrasound, we synthesized Pt nanoparticle and coated it on MPL (microporous layer), simultaneously. It has being revealed that ultrasound is an effective way to create metal nanoparticle because of ultrasound’s cavitation effect.[3] Bang et al explained about cavitation effect. Bubble explosion provides huge pressure and energy for a chemical reaction if the bubble size reached the critical point under ultrasound irradiation.[4] In addition, ultrasound has a micro jet effect, which has ability to clean a substrate and coat nanoparticles on it.[5] In our study, ultrasound applied to form a catalyst layer and the we adopted it for fabricating MEA (Membrane Electrode Assembly) of single cell. The MEAs were compared with MEA fabricated by a conventional method with Pt/C catalyst. To verify a formation of nanoparticle via a cavitation effect of ultrasound, we used UV-visible spectroscopy and observed spectrum change nearby 450 nm which is known for Pt 4+ after ultrasound’s irradiation.[6] To coat Pt nanoparticles on the carbon paper, we prepared carbon papers fixed at an acrylic frame in platinum precursor solution with reducing agent. Ultrasound was irradiated at various conditions. For example, time and power of irradiation, concentrations of the precursor and the reducing agent were changed to find an optimum condition for a sonochemical coating. As shown in Figure 1, images of the carbon papers acquired by FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive Spectroscopy) were used for checking platinum distribution. Cathode’s catalyst layer of MEAs was prepared by sonochemical method and anode’s catalyst layer was formed by spraying Pt/C on carbon paper. The MEAs were fabricated using hot-pressing without ionomer. Figure 2 shows I-V curve of the MEAs made at the 12 W of ultrasound power for 120 min and 90 min. To figure out experiment condition effect, we are still carrying out single tests and perform a characterization of MEA to elucidate the difference between MEAs. All the results investigated in the study will be presented with in-depth discussion. Figure 1