Low-Pt electrocatalyst

Demonstrate the performance of combined features derived from the best performing low-Pt electrocatalyst and the optimal MEA structure in a short stack fuel cell. 

The concept of a promoter can also be extended to the case of substances which enhance the performance of an electrocatalyst by accelerating the rate of an electrocatalytic reaction. This can be quite important for the performance, e.g., of low temperature (polymer electrolyte membrane, PEM) fuel cells where poisoning of the anodic Pt electrocatalyst (reaction 1.7) by trace amounts of strongly adsorbed CO poses a serious problem. Such a promoter which when added to the Pt electrocatalyst would accelerate the desired reaction (1.5 or 1.7) could be termed an electrocatalytic promoter, or electropromoter, but this concept will not be dealt with in the present book, where the term promoter will always be used for substances which enhance the performance of a catalyst. 

Brankovic SR, Wang JX, Adzic RR. 2001b. Pt submonolayers on Ru nanoparticles—A novel low Pt loading, high CO tolerance fuel cell electrocatalyst. Electrochem Solid State Lett 4 A217-A220. 

Wee, J. H., Lee, K. Y, and Kim, S. H. Fabrication methods for low-Pt-loading electrocatalysts in proton exchange membrane fuel cell systems. Journal of Power Sources 2007 165 667-677. 

This review will focus on the applications of XAS in the characterization of low temperature fuel cell catalysts, in particular carbon supported Pt electrocatalysts, Pt containing alloys for use as anode and... 

Adzic, R. et al.. Low Pt loading fuel cell electrocatalysts, 271, 2006 Annual Merit-Review and Peer Evaluation Report, DOE Hydrogen, Fuel Cells and Infrastructure Technologies Program, Arlington, VA, May 16-19, 2006. 

Zeis, R. et al., Platinum-plated nanoporous gold An efficient, low Pt loading electrocatalyst for PEM fuel cells, J. Power Sources, 165(1), 65, 2007. 

The possible complete replacement of Pt or Pt alloy catalysts employed in PEFC cathodes by alternatives, which do not require any precious metal, is an appropriate final topic for this section. Some nonprecious metal ORR electrocatalysts, for example, carbon-supported macrocyclics of the type FeTMPP or CoTMPP [92], or even carbon-supported iron complexes derived from iron acetate and ammonia [93], have been examined as alternative cathode catalysts for PEFCs. However, their specific ORR activity in the best cases is significantly lower than that of Pt catalysts in the acidic PFSA medium [93], Their longterm stability also seems to be significantly inferior to that of Pt electrocatalysts in the PFSA electrolyte environment [92], As explained in Sect. 8.3.5.1, the key barrier to compensation of low specific catalytic activity of inexpensive catalysts by a much higher catalyst loading, is the limited mass and/or charge transport rate through composite catalyst layers thicker than 10 pm. 

In addition to having a good CO tolerance, Pt-Ru electrocatalysts must also have a high activity for H2 oxidation. Comparison of the mass-specific activity of a PtRu2o electrocatalyst with a commercial Pt-Ru 1 1 alloy electrocatalyst for the oxidation of pure H2 showed that its activity is tluee times that of the commercial alloy. This indicates that even for a low Pt coverage on Ru, its activity for H2 oxidation is preserved, a prerequisite for an active CO tolerant catalyst. Comparing the CO tolerance of the PtRu2o electrocatalyst with that of two commercial Pt-Ru alloy electrocatalysts for the oxidation of 1095 ppm CO in H2 confirmed the exceptional stability of the former (Fig. 20) the measurements... 

Fuel cell electrocatalysis also has advanced significantly with innovations in the preparation of active Pt-Ru catalysts. A new type of electrocatalyst was developed, consisting of a Pt submonolayer on Ru nanoparticles. It has high CO tolerance and a very low Pt content. Its synthesis was facilitated by the discovery of electroless deposition of Pt on Ru nanoparticles that can be controlled so that most (> 90%) Pt atoms become available for the catalytic reaction. The catalytic activity of PtRu2o prepared by this method affords considerable advantages in the oxidation of H2, CO, and CH3OH compared with commercial Pt-Ru alloys. 

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... 

Ramaswamy N, Arruda TM, Wen W, Hakim N, Saha M, Gulla A, Mukcrjee S (2009) Enhanced activity and interfacial durability study of ultra low Pt based electrocatalysts prepared by ion beam assisted deposition (IBAD) method. Electrochim Acta 54 6756-6766 Wu J, Yuan XZ, Martin JJ, Wang H, Zhang J, Shen J, Wu S, Merida W (2008) A review of PEM fuel cell durability degradation mechanisms and mitigation strategies. J Power Sources 184 104-119... 

Develop and apply eombinatorial powder synthesis platform based on spray pyrolysis for diseovery of high-performanee low-Pt eathode electrocatalysts. 

Galvanic displacement method is also often used for synthesizing catalysts. By this method, low Pt-content electrocatalysts can be obtained. For example, a carbon-supported core—shell structured electrocatalyst with bimetallic IrNi as the core and platinum monolayer as the shell has been successfully synthesized using this method. In this synthesis, IrNi core supported on carbon was first synthesized by a chemical reduction and thermal annealing method and a Ni core and Ir shell structure could be formed finally. The other advantage of this method is that the Ni can be completely encased by Ir shell, which will protect Ni dissolve in acid medium. Secondly, IrNi PtML/C core—shell electrocatalyst was prepared by depositing a Pt monolayer on the IrNi substrate by galvanic displacement of a Cu monolayer formed by under potential deposition (UPD). 

Ignaszak A, Teo C, Ye S, Gyenge ED. Pt-Sn02-Pd/C electrocatalyst with enhanced activity and durability for the oxygen reduction reaction at low Pt loading the effect of carbon support type and activation. / Phys Chem C 2010 114(39) 16488-504. 

The long-term stability of Pd-based electrocatalysts is one of the unavoidable issues for PEM fuel cell applications. Pd-Pt-based ORR catalysts are more stable than Pd-transition metal alloys under harsh fuel cell conditions, but may still not meet the long-term fuel cell operation requirement due to the Pd leaching out. Future research may focus on improving the durability of Pd-based catalysts by surface modification and composition optimization. Core-shell type of catalyst with Pd-based materials as the core and Pt as the shell may be one of the most promising candidates to be used in the automotive fuel cell due to its low Pt content and high activity and stability. 

Esmaeilifar A, Rowshanzamir S, Eikani MH, Ghanzanfari E (2010) Synthesis methods of low Pt-loading electrocatalysts for proton exchange membrane fuel cell systems. Eneigy 35 (9) 3941-3957... 

Recent intensive research efforts have led to the development of less expensive and more abundant electrocatalysts for fuel cells. This book aims to summarize recent advances of electrocatalysis in oxygen reduction and alcohol oxidation, with a particular focus on low- and non-Pt electrocatalysts. The book is divided into two parts containing 24 chapters total. All the chapters were written by leading experts in their fields from Asia, Europe, North America, South America, and Africa. The first part contains six chapters and focuses on the electro-oxidation reactions of small organic fuels. The subsequent eighteen chapters cover the oxygen reduction reactions on low- and non- Pt catalysts. 

---