Platinum is a very attractive metal in the jewelry industry. It doesn’t tarnish or oxidize when exposed to air or water, and it’s a great choice for rings because of its hypoallergenic properties and its beautiful silver-white metallic appearance.
Platinum makes desirable jewelry, but its most important applications are industrial. Platinum is the primary component of catalytic converters, pollution control devices to convert dangerous automotive emissions to safe non-toxic substances. Platinum is also used in numerous electronic components, diesel engines, and as petroleum and chemical refining catalysts. Platinum is used in glass, silicones, computer hard disks, medicines and medical devices, and dental alloys.
Platinum is the primary catalyst used in proton exchange fuel cells, an environmentally-friendly power generation source for vehicles including forklifts, automobiles, buses, airplanes, boats, motorcycles, submarines, satellites and space capsules. Fuel cell technology combines oxygen and hydrogen to form water and electricity.
One of the components of a proton exchange fuel cell is the Membrane Electrode Assembly (MEA). The MEA has layers of platinum in carbon black, which catalyzes the reaction of hydrogen and oxygen. When manufacturing or developing an MEA, the aim is to maximize the surface area of platinum that is electrically connected to the conducting support. Any loss of surface area decreases the efficiency of the device. Platinum loss can sometimes occur when high currents effectively corrode the carbon-black support liberating the active metal allowing it to migrate from the electrode surface to the adjacent polymer electrolyte. A typical material for electrolyte is Nafion®. The presence of platinum in the Nafion will hinder hydrogen ion mobility in the electrolyte.
What is an effective way to analyze an MEA and determine if platinum has migrated from the catalytically active layers into the adjacent Nafion electrolyte? X-ray Photoelectron Spectroscopy (XPS), a technique for analyzing the surface chemistry of a material.
The MEA consists of layers which are tens of microns thick. The platinum-containing anode and cathode layers are around the thicker Nafion electrolyte. The Nafion is electrically insulating, but allows transport of hydrogen ions. These layers are too thick for conventional XPS depth profiling so sectioning is required for XPS analysis. Cross sectioning, among other techniques, enables the detection of subtle diffusion of platinum in these nanometer scale layers.
Read this XPS Characterization of a Membrane Electrode Assembly from a Proton Exchange Fuel Cell application note to get more details about the methodology, the cross-sectioning technology, images, linescans, and results.