Abstract
The prototype chalcogenide electrocatalyst RhxSy was probed in situ via a synchrotron-based X-ray absorption near-edge structure (XANES) technique to elucidate specific sites and modes of water activation during oxygen reduction reaction. X-ray diffraction revealed a mixture of phases (Rh2S3, Rh3S4, and Rh17S15). Theoretically generated XANES on a variety of geometries of O(H) adsorption on the predominant Rh3S4 phase were compared to the experimental data. We show for the first time that the electrocatalyst first adsorbs O(H) in a onefold configuration at lower potentials and n-fold at potentials greater than 0.80 V. This expectedly has important consequences for oxygen reduction reaction on alternative chalcogenide materials.
High Performance Polymer Electrolyte Fuel Cells with Ultra-Low Pt Loading Electrodes Prepared by Dual Ion Beam Assisted Deposition
M. Saha, A. F. Gulla, R. Allen and S. Mukerjee Electrochimica Acta, 51, 4680 (2006)
Abstract
Ultra-low pure Pt-based electrodes (0.04–0.12 mgPt/cm2) were prepared by dual ion-beam assisted deposition (dual IBAD) method on the surface of a non-catalyzed gas diffusion layer (GDL) substrate. Film thicknesses ranged between 250 and 750 Å, these are compared with a control, a conventional Pt/C (1.0 mgPt(MEA)/cm2, E-TEK). The IBAD electrode constituted a significantly different morphology, where low density Pt deposits (largely amorphous) were formed with varying depths of penetration into the gas diffusion layer, exhibiting a gradual change towards increasing crystalline character (from 250 to 750 Å). Mass specific power density of 0.297 gPt/kW is reported with 250 Å IBAD deposit (0.04 mgPt/cm2 for a total MEA loading of 0.08 mgPt/cm2) at 0.65 V. This is contrasted with the commercial MEA with a loading of 1 mgPt(MEA)/cm2 where mass specific power density obtained was 1.18 gPt/kW (at 0.65 V), a value typical of current state of the art commercial electrodes containing Pt/C. The principal shortcoming in this effort is the area specific power density which was in the range of 0.27–0.43 W/cm2 (for 250–750 Å IBAD) at 0.65 V, hence much below the automotive target value of 0.8–0.9 W/cm2 (at 0.65 V). An attempt to mitigate these losses is reported with the use of patterning. In this context a series of patterns ranging from 45 to 80% Pt coverage were used in conjunction with a hexagonal hole geometry. Up to 30% lowering of mass transport losses were realized.
Towards Improving the Performance of PEM Fuel Cells by Using Mix Metal Electrodes Prepared by Dual Ion Beam Assisted Deposition
Abstract
Dual ion beam assisted deposition (IBAD) has been used to manufacture selected Pt-based alloy/mix (Pt–Co and Pt–Cr) electrodecatalysts by direct metallization of a standard E-TEK gas diffusion layer (GDL). Their kinetics for oxygen reduction reaction and their performance in a proton exchange membrane fuel cells (PEMFCs) are presented. Activity enhancement, normalized to electrochemical surface area and mass activity, of 38.99 mA/cm2 (Pt–Co) and 27.21 mA/cm2 (Pt–Cr) are reported relative to an IBAD Pt electrode-catalyst. We report a significant new development in terms of materials and mass-manufacturability for PEMFC applications
Investigation of Durability Issues of Selected Non-Fluorinated Polymer Exchange Membranes for Fuel Cell Applications
Abstract
Nonfluorinated sulfonic acid membranes are a group of promising candidate materials for the commercialization of proton exchange membrane fuel cell (PEMFC) technology. However, one of the main obstacles is that the harsh fuel cell environment may originate different modes of degradation and aging processes that result in either chemical or morphological alteration in these membranes. The effect of peroxide radicals on PEM durability is of particular interest because a common feature of many hydrocarbon-based membranes is that the building block consists of sulfonic acid-substituted aromatic rings, which are much more sensitive to radical attack than the Teflon-like backbone in perfluorinated sulfonic acid type materials. In this work, we attempt to provide answers to the hydroxyl radical initiated durability issues at the PEM and electrocatalyst interface by analyzing the performance of two novel membranes, sulfonated poly(arylene ether sulfone) and sulfonated poly(ether ether) ketone, using a
newly designed durability evaluation method under fuel cell-like conditions. This method is able to separate the membrane evaluation process into cathode and anode aspects. Under experimental conditions in this work, degradations in SPES-40 samples were found happening at the cathode (oxygen) side of the PEMFC.