The Synthesis of Platinum and Non-Precious Metal Catalysts Based on Carbonized Polyaniline Matrix and Its Application to Fuel Cell

Abstract

The polymer electrolyte membrane fuel cells (PEMFCs) are regarded as a promising energy conversion device because of high efficiency and eco-friendly energy generation. However, the prohibitive cost of PEMFCs still remains big problem for its a commercialization. The platinum which is considered promising metal for oxygen reduction reaction (ORR) accounts for the biggest part of the cost. Therefore, most researches have concentrated on reducing the amount of platinum or developing non-precious metal catalyst. In this study, we employed nitrogen doped carbon to improve performance of Pt catalyst. A lot of researches have shown that Pt supported on the nitrogen doped carbon is prospective catalyst for PEMFC.[1] And also, we applied the nitrogen doped carbon to non-precious metal catalyst. The nitrogen doped carbon was promising candidate to substitute Pt based catalyst, because the nitrogen doped carbon have catalytic activity without metal such as platinum.[2] The synthesis method to make nitrogen doped carbon is very diverse. In this study, we adopted a method that utilized carbonized polyaniline (PANI). The PANI have been used as a source of nitrogen doped carbon. Gavrilov et al. reported carbonized PANI supported Pt catalyst for ORR.[3] Their catalysts had good catalytic activity in acidic and alkaline media. Wu et al. reported that PANI-M-C (M = Fe and/or Co) which was comparable to the performance of conventional Pt/C catalyst was successfully synthesized with PANI.[4] We suggested differentiated method from other researches to synthesized PANI based catalyst. Our experiment process to make PANI based catalysts are like follows. First of all, metal precursor (Pt or Fe), aniline monomer and carbon black was fully mixed. The mixture was irradiated by ultrasound and the irradiated mixture was filtered. After filtering, we obtained M-PANI-C (M = Pt or Fe, C = carbon black). Finally, the M-PANI-C was heat-treated in nitrogen atmosphere to carbonize PANI. In our experiment, the role of metal precursor was not only metal source but also oxidant for polymerization of aniline. And the ultrasound made the metal particle well dispersed in PANI matrix. Consequently, this method suggested more simple process than other methods and made it possible to polymerize aniline without any oxidant. Fig 1. is the linear sweep voltammetry(LSV) result of Pt-PANI-C. The LSV curves shows that the synthesized Pt-PANI-C catalyst has better performance for ORR than conventional Pt/C catalyst. The Pt contents of Pt-PANI-C was 10 wt%, which is only half the Pt content of Pt/C catalyst. (Pt contents could be obtained by ICP-MS analysis) This result indicates that the PANI was successfully applied to ORR catalyst and the PANI could enhance performance of Pt based catalyst. Fig 2. is the LSV result of Fe-PANI-C catalyst in alkaline electrolyte. The Fe-PANI-C catalyst was acid leached for removing impurity and iron oxide before electrochemical analysis. The ORR performance of Fe-PANI-C catalyst is comparable to Pt/C catalyst. The both of catalysts were analyzed with various tools to characterize catalysts and determine the reason why performance was improved. And furthermore, the catalysts were applied to single cell test and we evaluated the single cell performance of catalysts. All the results investigated in the research will be presented with in-depth discussion.