Investigation of platinum utilization and morphology in catalyst layer of polymer electrolyte fuel cells

Platinum utilization in the gas-diffusion catalyst layer and thin-film cata lyst layer is investigated. The morphology of PTFE and Nafion in a simulate d catalyst layer is examined by scanning electronmicroscopy (SEM) and trans mission electron microscopy (TEM). The results show that the platinum utili zation of the thin-film catalyst layer containing only Pt/C and Nafion is 4 5.4%. The low utilization is attributed to the fact that the electron condu ction of many catalyst particles is impaired by some thick Nafion layers or clumps. For the gas-diffusion (E-TEK) electrode, the platinum utilization is mainly affected by the proton conduction provided by Nafion. The blockin g effect of PTFE on the active sites is not serious. When the electrode is sufficiently impregnated with Nafion by an immersion method, the platinum u tilization can reach 77.8%. Transmission electron micrographs reveal that a lthough some thick Nafion layers and clumps are observed in the Pt/C + Nafi on layer, the distribution of Nafion in the catalyst layer is basically uni form. The melted PTFE disperses in the catalyst layer very uniformly. No la rge PTFE clumps or wide net-like structure is observed. The reactant gas ma y have to diffuse evenly in the catalyst layer. (C) 1999 Elsevier Science S .A. All rights reserved.