SYNTHESIS, CHARACTERIZATION AND INVESTIGATION OF ELECTOCATALYTICAL PROPERTIES OF PLATINUM TERNARY CATALYSTS IN ORDER TO BE USED AT THE CATHODE OF A PEM FUEL CELL


Thesis Type: Post Graduate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2008

Student: SİLVER GÜNEŞ

Consultant: FATMA ÇİĞDEM GÜLDÜR

Abstract:

Fuel cells are devices that enables the conversion of chemical energy to useful electricity by high efficiency. Among various types of fuel cells developed, PEM (Polymer Electrolyte Membrane) fuel cell is the most promising candidate for uses as a portable power source in transportation due to its advantages such as low working temperature (generally between 80-90 C°), resistance to corrosion and low volume. One of the major problems confronting the commercialization of PEM fuel cells is that they need the use of very expensive platinum based electrocatalysts. The voltage produced by PEM fuel cell is limited by the low kinetic rate of the oxygen reduction reaction (ORR) occuring at the cathode. Thus, studies on PEM fuel cells are focused on developing a catalyst that will be used in the electrocatalysis of the oxygen reduction reaction. In this study, it was aimed to develop cheap and active catalysts that can be used in the electrocatalysis of the ORR reaction at the cathode of the PEM fuel cell. The catalysts were prepared by depositing the ternary catalysts of platinum with the transition metals; Ag, Cu and Fe on carbon support by wet impregnation reduction method and were characterized by various methods including N2 physisorption, XRD, SEM, EDX and cyclic voltammetry (CV). As vii the result of the characterization studies it was observed that the catalysts have macroporous structure and surface areas varying between 152 and 209 m2/g. The mean particle size of platinum is varying between 3.66 and 16.35 nm and it was seen that catalysts with higher platinum loadings have smaller particle sizes. In the cyclic voltammetry measurements it was seen that the choice of the binding agent used in the preparation of the electrode is very important. While the electroactive surface areas of the PTFE-binded catalyst films is low, catalysts prepared with nafion have quite high electroactive surface area. PtAgFe/C-611 has the largest electroactive surface area with 557,25 cm2/mg. It was seen that that PtAgFe/C catalysts give the highest activity and the mass activities are inversely proportional to the platinum mass loading. Selectivity of the catalysts towards the oxygen reduction reaction was investigated by rotating ring-disk voltammetry technique. It was seen that the peroxide formation percentage is higher at the catalysts having less platinum content. As a result, it was concluded that within the catalysts synthesized in this study PtAgFe/C-611 and PtCuFe/C-611 can be used as alternative catalyst at the cathode of the PEM fuel cell.