Pt nanoparticle electrocatalyst

This section provides a comprehensive overview of recent efforts in physical theory, molecular modeling, and performance modeling of CLs in PEFCs. Our major focus will be on state-of-the-art CLs that contain Pt nanoparticle electrocatalysts, a porous carbonaceous substrate, and an embedded network of interconnected ionomer domains as the main constituents. The section starts with a general discussion of structure and processes in catalyst layers and how they transpire in the evaluation of performance. Thereafter, aspects related to self-organization phenomena in catalyst layer inks during fabrication will be discussed. These phenomena determine the effective properties for transport and electrocatalytic activity. Finally, physical models of catalyst layer operation will be reviewed that relate structure, processes, and operating conditions to performance. 

The solid curve in Figure 6.19 displays the cyclic voltammetric response of a carbon-supported high surface area Pt nanoparticle electrocatalyst in perchloric acid electrolyte under de-aerated conditions. The hydrogen adsorption range between... 

Li X, Liu J, He W, Hutmg Q, Yang H (2010) Influence of the composition of core-shell Au-Pt nanoparticle electrocatalysts for the oxygen reduction reaction. J Colloid Interface Sd 344 132... 

Zhang, S., et al., Carbon nanotubes decorated with Pt nanoparticles via electrostatic self-assembly a highly active oxygen reduction electrocatalyst, journal of Materials Chemistry,... 

Figure 6.19. Experimental cyclic voltammograms of carbon-supported high surface area nanoparticle electrocatalysts in deaerated perchloric acid electrolyte. Solid curve pure Pt dashed curve Pt5oCo5o alloy electrocatalyst. Inset blow up of the peak potential region of Pt—OH and Pt— formation. Scan rate 100 mV/s. Potentials are referenced with respect to the reversible hydrogen electrode potential (RHE).

Figure 6.20. Experimental linear sweep voltammogram of carbon-supported high surface area nanoparticle electrocatalyst in oxygen-saturated perchloric acid electrolyte (room temperature). Solid curve pure Pt dashed curve Pt50Co50 alloy electrocatalyst. Inset a blow up of the kinetically controlled ORR regime. Inset b comparison of the specific (Pt surface area normalized) current density of the Pt and the Pt alloy catalyst for ORR at 0.9 V.

Catalyst Structure D in Fig. 6.21 represents a structurally distinct electrocatalyst compared to catalysts A-C. Unlike A-C, structure D contains no base-metal near the top layer of the smooth or high surface area catalyst. Catalysts like that in Figure 6.21D were prepared [126-129] by rapid electrochemical de-alloying (preferred leaching of the base-metal) of base-metal-rich precursor Pt alloys. The electrocatalytic ORR activities of the catalyst materials obtained after de-alloying exceeded pure Pt nanoparticle catalysts by a factor of 4-6 x. 

In this chapter we review studies, primarily from our laboratory, of Pt and Pt-bimetallic nanoparticle electrocatalysts for the oxygen reduction reaction (ORR) and the electrochemical oxidation of H2 (HOR) and H2/CO mixtures in aqueous electrolytes at 274—333 K. We focus on the study of both the structure sensitivity of the reactions as gleaned from studies of the bulk (bi) metallic surfaces and the resultant crystallite size effect expected or observed when the catalyst is of nanoscale dimension. Physical characterization of the nanoparticles by high-resolution transmission electron microscopy (HRTEM) techniques is shown to be an essential tool for these studies. Comparison with well-characterized model surfaces have revealed only a few nanoparticle anomalies, although the number of bimetallics... 

Zeis R, Mathur A, Fritz G, Lee J, Erlebacher J (2007) Platinum-plated nanoporous gold an efficient, low Pt loading electrocatalyst for PEM fuel cells. J Power Sources 165 65-72 Wu H, Wexler D, Wang G (2009) PtjNi alloy nanoparticles as cathode catalyst for PEM fuel cells with enhanced catalytic activity. J Alloy Compd 488 195-198... 

Characterize Pt/Ru electrocatalysts prepared by a new method involving a spontaneous deposition of Pt on Ru nanoparticles. 

Fig. 2.24 TEM of homogeneously alloyed Cu/Pt nanoparticles on carbon (a) and the onion-type Pt Cu electrocatalyst (b). The inset on micrograph (b) shows small Pt nanoparticles (1-2 nm) decorating larger copper nanoparticles (6-8nm).

Liu J, Cao J, Huang Q et al (2008) Methanol oxidation on carbon-supported Pt-Ru-Ni ternary nanoparticle electrocatalysts. J Power Sources 175 159-165... 

In general, non-noble metal alloy nanoparticles have shown some methanol tolerance effects, but their activity towards ORR is lower than that of Pt/C. Furthermore, it has been found that the non-precious metal catalysts do not present the required stability in the acidic environment, even in the case of Pd (at high potential). On the other hand, some works have shown that this instability (dissolution), mainly of the non-noble metal, can be overcome by the addition of small amounts of stabilizers like Au. Based on this, Mathiyarasu and Phani [30] examined the effect of the addition of Au, Ag and Pt on the activity and stability of several Pd-Co/C electrocatalysts. Results showed higher ORR activities for Pd-Co-Pt/C, equal to that of a commercial Pt/C electrocatalyst. 

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