Abstract
Achieving high performance and durability at low Pt loads is an important challenge for polymer electrolyte fuel cells (PEFCs). We investigated the effect of catalyst Pt loading percentage (wt % Pt) on the performance and durability of an ultrahigh surface area carbon black (CB) with a large nanopore volume using morphological observations, nitrogen adsorption, and electrochemical performance measurements. The ratio of the surface areas of Pt on the interior and exterior surfaces of the CB affects the penetration of the ionomer into the nanosized pores. When the exterior Pt surface area is larger than that of the interior, the oxygen diffusion resistance in the ionomer increases and the performance deteriorates due to the thick covering of the ionomer on the exterior Pt. Based on durability testing that combines startup, shutdown, and galvanostatic load cycling, the main deterioration factors are dependent upon the Pt interparticle distance and the thickness of the catalyst layer, which vary with the wt % Pt. The advanced characterization and optimization of the various wt % Pt on an ultrahigh surface area CB, combined with the extensive performance and durability testing, have provided an unprecedented understanding of the reaction sites, mass transport characteristics, and stability, which are crucial for their practical application in PEFCs.
Highlights
Polymer electrolyte fuel cells (PEFCs) generate electricity from hydrogen (H2) and oxygen (O2) without producing carbon dioxide during electricity generation, in contrast to fossil fuels
In the membrane electrode assembly (MEA), H2 is supplied to the anode catalyst layers (CLs), and air or O2 is supplied to the cathode CL; the CLs are composed of a catalyst consisting of Pt nanoparticles on a high-surface area support and an ionomeric binder
Vulcan carbon blacks (CBs), and Ketjenblack, among others, are often used as carbon support materials, and it has been found that the structure and morphology of the carbon support have a great effect on the fuel cell performance and durability.[3−8] We considered that the efficient supply of protons and oxygen is crucial at a high current density
Summary
Polymer electrolyte fuel cells (PEFCs) generate electricity from hydrogen (H2) and oxygen (O2) without producing carbon dioxide during electricity generation, in contrast to fossil fuels. We suggested that the amount of hysteresis volume in the isotherm of the N2 adsorption measurement method is a parameter that indicates the state of ionomer coverage in the pores of the catalysts.[38] In addition, the effect of wt % Pt on the cell performance was investigated.[18] Rahman et al used two supports with different specific surface areas (about 1300 and 800 m2/g) to prepare a catalyst in which the wt % Pt was varied from 25 to 40 wt %. We examined the optimum CL structure for high durability by carrying out durability testing including startup, shutdown, and galvanostatic load cycling operation
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