Stability of Ultra-low Pt Anodes for Polymer Electrolyte Fuel Cells Prepared by Magnetron Sputtering

Abstract

Anodes for polymer electrolyte fuel cells (PEFC) with ultra-low platinum loadings (3, 15 and 25 μg Pt /cm 2 ) were prepared by sputter deposition of platinum onto carbon cloth covered with a microporous carbon layer. Platinum nanoparticles as well as agglomerates were observed by TEM for all investigated Pt loadings. Sputtered anodes with Pt loadings of 15 and 25 μg Pt /cm 2 can be operated at currents up to 2 A/cm 2 without voltage losses compared with a commercial anode with 500 μg Pt /cm 2 . Anode loadings of 3 μg Pt /cm 2 yield a similar PEFC performance only at low current densities (<0.5 A/cm 2 ). Longevity tests at constant current density (0.5 A/cm 2 ) show nearly constant cell voltages for up to 1,000 h for an anode loading of 25 μg Pt /cm 2 . Lower Pt loadings (3 and 15 μg Pt /cm 2 ) lead to more distinct voltage losses, probably caused by CO traces in the hydrogen reactant gas. The CO poisoning is in part reversible by (electro)chemical oxidation of CO.

The Effect of Platinum Nanoparticle Distribution on Oxygen Electroreduction Activity and Selectivity

“…As reported in a previous investigation,15 if the sputtering deposition time is increased, a constant increase of the Pt amount on top of the carbon layer is obtained, but owing to the process conditions, the primary particle size remained constant (2±1 nm in diameter). For loadings lower than 3 μg Pt cm −2 dispersed Pt nanoparticles were observed, whereas Pt agglomerates were formed for loadings >20 μg Pt cm −2 ; if the Pt loading (i.e., deposition time) was further increased, extended particulate Pt layers were obtained.…”

“…As shown by the TEM images in Figure 1, primary particles of approximately 2–3 nm in diameter can be observed together with agglomerates of a few particles. It is worth highlighting that although on a flat surface a Pt loading of 2 μg Pt cm −2 results in some particle agglomeration (Figure 1), on high‐surface‐area carbon such a low loading is expected to result in isolated particles 15…”

Ultra‐low Mass Sputtered and Conventional Catalyst Layers on Plasma‐etched Nafion for PEMFC Applications

“…The membrane patterning approach has been demonstrated with membrane laser ablation , plasma modification in Ar, H 2 ‐He, Ar‐O 2 , and Ar‐SF 6 environments , and lithographic patterning . Plasma deposited Pt gas diffusion electrodes and catalyst coated membranes , Pt films in conjunction with restructured membranes , and sputter‐patterned Pt electrodes via a glancing angle deposition approach have also been examined to illustrate the benefits of microfabrication to PEMFC cell construction. These previous efforts on membrane restructuring and ultra‐low catalyst loading detail the capability of the various techniques for performance improvement in comparison to unmodified MEAs.…”

Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3Y Thin Films

“…The results (Figure ) show the formation of dense alloy material on top of the carbon black and thinner areas of alloy on the sidewalls, which breaks up and forms isolated nanoparticles further down into the GDL. The observations are similar to previous ones on Pt sputtered onto GDL . The leaching of the Y and formation of a Pt overlayer do not change the overall structure of the catalyst material, as observed by TEM (Figure ) and SEM (Figure S6 in the Supporting Information).…”

“…The latter process leads to an exponential decay of the amount of catalyst material with the depth into the GDL . For sputtered Pt, the exponential reduction in film thickness on the sides of the carbon particles eventually leads to breaking up of the film into nanoparticles …”