Alternative Catalyst Supports Deposited on Nanostructured Thin Films for Proton Exchange Membrane Fuel Cells

Abstract

A series of platinum-coated underlayer materials, alumina, gold, titanium carbide, and titanium disilicide, deposited by a high throughput magnetron sputtering method have been investigated as cathode catalyst supports in fuel cells. Orthogonal thickness gradients of the underlayer materials ͑0-100 nm planar equivalent͒ and the platinum top layer ͑0-75 nm planar equivalent͒ made up the 76 ϫ 76 mm libraries. The resulting catalyst films were characterized by surface profilometry, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical properties of the catalyst composition spreads were investigated simultaneously in 64-electrode proton exchange membrane fuel cells with emphasis placed on the determination of the electrochemical surface area ͑ECSA͒ as a function of underlayer thickness and chemistry. The present study shows that gold and titanium disilicide used as underlayers on 3M's nanostructured thin film supports lead to a loss of ECSA during operation. Migration and surface accumulation were observed when gold was used as underlayer material. For titanium disilicide, alloying and the generation of platinum silicide phases occurred. Alumina and titanium carbide were found to be potentially acceptable underlayer materials as well as alternative support materials on the basis of their influence on the catalyst surface area.Polymer electrolyte membrane fuel cells ͑PEMFCs͒ are promising power sources for automotive applications in the future. 1 The main environmental advantage of using PEMFCs in vehicles is the reduction of carbon dioxide emissions, pollutants, and consumption of fossil fuels. 2 To fully commercialize PEMFCs for automotive vehicles, their high production cost needs to be reduced while improving performance and durability. The core of a PEMFC, the membrane electrode assembly ͑MEA͒, consists of two electrocatalyst electrodes ͑anode and cathode͒ with gas diffusion layers ͑GDLs͒ on either side of the proton-conducting ion-exchange membrane. Each of these MEA components contributes to the overall performance, stability durability, robustness, and cost of a PEMFC, and thus research efforts have been focused on the improvement of the electrocatalyst and membrane properties. 3 Platinum or platinum alloys are commonly used as the catalyst on the anode side for the hydrogen oxidation reaction ͑HOR͒ and on the cathode side for the oxygen reduction reaction ͑ORR͒ in a PEMFC. These catalysts may consist of highly dispersed platinum particles ͑2-3 nm͒ supported on carbon blacks, activated carbon, or carbon nanotubes. A range of factors 4 are known to contribute to the significant performance degradation of PEMFCs that can occur during long-term operation or as a result of adverse operating conditions ͑e.g., fuel starvation on the anode side during start-up and shutdown 5 ͒. These include Pt-catalyzed corrosion of the carbon support, 6 oxidation and decomposition of the GDL, 7 dissolution or poisoning of the Pt catalysts on the cathode and anode side, 8 and degr...

Recent Progress on the Key Materials and Components for Proton Exchange Membrane Fuel Cells in Vehicle Applications

“…It has been reported that Pt monolayer catalysts, such as Pt ML /Pd/NiW/GDL and Pt ML /Pd/C, showed excellent durability in PEMFC tests [64], but their H 2 /Air performance needs further improvement by optimizing the ionomer distribution in the catalyst layer. The 3M nanostructured thin film (NSTF) catalyst is currently the sole practical example of an extended surface area catalyst shown to effectively address several critical issues facing cathode and anode catalysts for fuel cell vehicles, including the performance, cost, and durability [67]. The NSTF Pt68Co29Mn3 catalyst has been the workhorse cathode and anode of choice for a number of years and its CCM [68,69] generated a specific activity of 2.93 mA/cm 2 Pt and a mass activity of 0.18 A/mgPt at 0.9 V vs. RHE.…”

“…The mass activities of the NSTF Pt3Ni7 for ORR with standard treatment cover the range of 0.35 to 0.59 A/mg [70]. A proprietary GM additional pretreatment process can further substantially increase the mass activities over the standard treatment; 0.47 to 0.58 A/mg using the GM ORR protocol and 0.62 to 0.67 A/mg using the 3M protocol [67]. However, even though reasonable current densities are being realized at 650 mV in PEMFCs, the limiting current densities are still not optimally high.…”

“…Besides the Pt/C catalysts, Pt alloy catalysts, Pt-based NSTF catalysts and Pt monolayer catalysts are either commercially available or have been reported as being produced on a large-scale. The 3M Pt-based NSTF catalyst advocated by Debe [67] was reported to have a similar activity compared to Pt/C, but its performance degradation can be neglected in accelerated stress tests of PEMFCs. The activities and durability of various commercial Pt-alloy catalysts were reported by Wagner [92,93].…”

Advanced catalytic layer architectures for polymer electrolyte membrane fuel cells

“…These are composed of arrays of small (less than 1 µm length) organic whiskers, fully covered by a thin Pt or Pt‐based alloy catalyst layer (see Figure (b) and next section). 3M layers exhibit very promising performance in PEMFCs and have been subject of numerous original and review papers . Inspired by the success of the NSTFs, several groups came up with alternative structures.…”

“…3M layers exhibit very promising performance in PEMFCs and have been subject of numerous original and review papers. [37][38][39] Inspired by the success of the NSTFs, several groups came up with alternative structures. For example, in order to further decrease the amount of PGMs, it was proposed to co-sputter Pt with carbon 40 (Figure 1(c)), or to deposit it on spatially ordered carbon nanostructures, such as vertically aligned carbon nanotubes or nanofibers 32 (Figure 1 (d) and (e)).…”