Understanding Activity and Durability of Core/Shell Nanocatalysts for Fuel Cells
We review recent analyses of the various aspects related to the performance of core/shell nanocatalyst particles used as electrodes in proton exchange membrane fuel cells. These nanoparticles usually consist of a thin layer of pure Pt in the shell and a c
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Understanding Activity and Durability of Core/ Shell Nanocatalysts for Fuel Cells Rafael Callejas-Tovar and Perla B. Balbuena
Abstract We review recent analyses of the various aspects related to the performance of core/shell nanocatalyst particles used as electrodes in proton exchange membrane fuel cells. These nanoparticles usually consist of a thin layer of pure Pt in the shell and a core alloy made of a combination of metal elements that are targeted to meet two main objectives: reducing the catalyst price and enhancing the activity of the surface layer with respect to an equivalent particle made of pure Pt. Even though both objectives have been shown to be met, a huge challenge remains that is related to the long-term durability of the particle. This is because the less noble components are prone to relatively easy dissolution in the harsh acid conditions in which low-temperature fuel cells operate. The catalytic behavior of the nanoparticle towards the oxygen reduction reaction (ORR) and the evolution of the catalytic particle under this complex environment require a combination of experimental modern surface science and electrochemical techniques but also the formulation of models that allow a better understanding and a rational catalyst design. In this chapter, we review the state-of-the-art modeling of core/shell catalysts for the ORR. This involves various aspects that are intrinsic to the core/shell structure: surface segregation, metal dissolution, and catalytic activity. A number of methods ranging from ab initio density functional theory to classical molecular dynamics and Kinetic Monte Carlo are included in our discussion.
R. Callejas-Tovar Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA P.B. Balbuena (*) Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA Materials Science and Engineering Program, Texas A&M University, College Station, TX 77843, USA e-mail: [email protected] M. Shao (ed.), Electrocatalysis in Fuel Cells, Lecture Notes in Energy 9, DOI 10.1007/978-1-4471-4911-8_20, # Springer-Verlag London 2013
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R. Callejas-Tovar and P.B. Balbuena
Introduction
Proton exchange membrane fuel cells (PEMFCs) are promising green alternatives to replace fossil fuels in transportation applications. However, the high cost and poor catalytic efficiency of the electrocatalyst where the oxygen reduction reaction takes place are crucial challenges that need to be overcome in order to exploit this technology. The ORR is a kinetically slow reaction in which molecular oxygen is reduced and combines with protons producing water. Platinum has been widely used as electrocatalyst for the ORR in fuel cells, but its prohibitive cost and relatively sluggish ORR kinetics[1] have motivated the development of catalysts with improved efficiency and low cost. The use of nanoparticles to carry out the electrocatalysis of the ORR minimizes the required amount of precious material that is able to maximiz
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