Preparation And Catalytic Activity Investigation Of High Performance PEMFC Catalysts

Polymer electrolyte membrane fuel cell (PEMFC) is a high efficiency and environmental friendly energy conversion device which could be operated at low temperature and start-up in short time. It can be used both in distributed power stations and mobile devices such as cell phones, laptops, cars, and air crafts. Many countries, including China, are putting in a lot of money to boost the performance of PEMFC. However, the performance of PEMFC is still limited by several problems. Pt was used as the main catalyst at both anode and cathode of PEMFC, especially for the cathode. The Pt catalyst loadings should be high enough to guarantee the fuel cell performance. However, the high cost of Pt is the main obstacle for the commercial application of PEMFC. So it is essential to develop the efficient catalyst with low Pt loading, high catalytic activity and high stability. In our work, we designed both anode and cathode catalysts and characterized their performances.(1) We investigated the performance of sub-monolayer Au modified Pt nanoparticle catalyst toward formic acid electro-oxidation. Firstly, we used under potential deposition method to deposit sub/mono-layer Cu onto the surface of Pt nanoparticle. Secondly, the sample was put into the solution with gold ion and then Au replaced Cu in-situ. By these two steps, sub-monolayer Au was precisely deposited onto the surface of Pt nanoparticle and the coverage of Au on Pt could be controlled by the times of deposition. We characterized the Au modified Pt nanoparticle catalyst toward formic acid electro-oxidation compared with pure Pt nanoparticle. Experimental results showed that the catalytic activity of Au modified Pt nanoparticle was enhanced by23-fold compared with pure Pt nanoparticle at a low potential (-0.2V). Interestingly, Au had almost no catalytic activity toward formic acid electro-oxidation, but as the coverage of Au on Pt increased, the performance of this catalyst increased. The much enhanced catalytic activity could be ascribed to a Pt surface ensemble effect, which induced changing of the reaction paths. These results showed great potential to rationally design more active and stable nanocatalysts by modifying the Pt surface with otherwise inactive materials.(2) We fabricated nanoporous gold leaf (NPG) supported Pt or PtCu alloy catalysts by photoreduction method and investigated the performance of those catalysts towards oxygen reduction reaction. Traditional deposition methods, chemical deposition and under potential deposition, have some drawbacks such as high toxicity of reducing regent and complex of fabrication procedure. Photoreduction is a simple and environmental friendly method to deposit metal onto NPG NPG was floating at the surface of solution containing Pt ion or PtCu ions. Then NPG and photocatalyst were connected by a copper wire. After irradiation under visible light, photocatalyst generated photo-induced electrons which were transported to NPG Photo-induced electrons reduced Pt ion or PtCu ions in solution and deposited Pt or PtCu alloy onto the surface of NPG The amount of Pt or PtCu alloy increased with increasing irradiation time. We investigated the oxygen reduction reaction performances of nanoporous gold leaf supported Pt (NPG-Pt) and nanoporous gold leaf supported PtCu alloy (NPG-PtCu) compared with commercial Pt/C catalyst. It was demonstrated that both NPG-Pt and NPG-PtCu catalysts were superior to commercial Pt/C catalyst which was caused by the high Pt utilization in NPG supported catalysts. As the electronic structure of Pt was influenced by Cu, NPG-PtCu catalyst showed much improved activity than NPG-Pt catalyst.