To investigate the effect of load cycling, platinum (Pt) and platinum-cobalt (PtCo) fuel cell catalysts with different particle sizes were prepared and evaluated for their durability against load cycling. The particle size of the Pt and PtCo catalysts was controlled by changing the catalyst loading and by applying heat treatment. Pt catalysts with particle sizes of 2–3 nm and 4–5 nm and PtCo catalysts with sizes of 3–4 nm, 4–5 nm and 7–8 nm were obtained. A potential sweep from 0.65 V to 1.05 V was applied to the cathode of membrane electrode assemblies (MEAs) prepared with these catalysts,and the degradation of their mass activity and cell voltage were evaluated. As a result of this investigation, it was found that Pt catalysts with particle sizes of 4–5 nm and PtCo catalysts of particle sizes 7–8 nm showed better stability against potential sweep, with the Pt catalysts of sizes 4–5 nm showing the best stability of all the catalysts tested.
After optimization of the preparation procedure and the alloy composition of a PtCo catalyst, we found that MEA of the PtCo catalyst could show better I-V performance than that of a Pt catalyst. To improve the stability of a carbon support, we have evaluated various types of carbon, and we found a graphitized carbon could show better stability than a normal carbon. We also evaluated the PtCo catalyst on the graphitized carbon to achieve both better ORR activity and better stability of carbon, but the PtCo catalyst on the graphitized carbon could not show any ORR activity improvement due to the larger particle size of PtCo. After exploring new carbons, we could find a unique carbon which has higher surface area and better stability than a normal carbon. We prepared the PtCo catalyst on the carbon, and this catalyst could show good balance between the ORR activity and the carbon stability.
Electrocatalytic materials for oxygen reduction reaction, currently dominated by platinum/carbon catalyst is marred by drawbacks such as use of copious amount of Pt and use of “non-green” sacrificial reducing agent (SRA) during its synthesis. A single stroke remedy for these two problems has been achieved through an in-situ aqueous photoreduction void of even trace amounts of SRA with an enhanced activity. Reduction of PtCl62− salt to Pt nano particles on carbon substrate was achieved solely using solar spectrum as the source of energy and TiO2 as photocatalyst. Here, we demonstrate that this new procedure of photoreduction, decorates Pt over different types of conducting allotropes with the distribution and the particle size primarily depending on the conductivity of the allotrope. The Pt/C/TiO2 composite unveiled an ORR activity on par to the most efficient Pt based electrocatalyst prepared through the conventional sacrificial reducing agent aided preparation methods.
The cell performances under low or high relative humidity were examined for Pt / C cathode catalysts of various kinds of carbon support. No significant difference of cell performance were observed among Vulcan XC-72, Graphitized Vulcan XC-72, HSAC-1 (Surface Area = c.a. 800 m2 g-1, particle size = c.a. 30 nm), and HSAC-2 (Surface Area = c.a. 800 m2 g-1, particle size = c.a. 10 nm). Heat treatment process to improve the stability decreased the cell performance especially under low relative humidity. It was suggested by the titration of catalysts that the loss of hydrophilic organic group on the surface of carbon support by the heat treatment of catalysts was one of the reasons. The effect of the weight ratio of ionomer to carbon (I / C) was also examined. For example, in the case of Vulcan XC-72 support, the best I / C for the cell performance was 0.9.
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