Mark K. Debe

Influence of Anode GDL on PEMFC Ultra-Thin Electrode Water Management at Low Temperatures

In addition to meeting cost, durability, and rated performance targets, PEM fuel cell systems for automotive traction applications additionally need the capability to transiently attain relatively high current densities at low temperatures to provide drive-away power. Additionally, the system ideally would be robust towards atypical shutdown/restart events which may leave the fuel cell stack in a relatively flooded state.

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

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 equivalent) and the platinum top layer (0-75 nm planar equivalent) made up the 76 × 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 (ECSA) as a function of underlayer thickness and chemistry. The present study shows that gold and titanium disilicide used as underlayers on 3Ms 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.

A New Paradigm for PEMFC Ultra-Thin Electrode Water Management at Low Temperatures

In this paper, we provide initial results of a novel method which dramatically improved the performance of ultra-thin electrode polymer electrolyte membrane fuel cells under highly water-condensing operating conditions, realized via modification of the anode gas diffusion layer and utilization of reduced anode reactant pressures, including sub-atmospheric pressure down to 20kPa. Measurements indicated that the sub-atmospheric anode reactant acted to greatly reduce the water flux exiting out the cathode, likely reducing cathode water flooding and oxygen transport limitations.

Catalytic Activity of Pt1-xNix (0 < x < 0.8) Measured on High Surface Area NSTF-Coated GC Disks

Intermixed Pt1-xNix (0 < x < 0.8) and Pt were sputter-deposited onto high surface area, NSTF-coated GC disks and studied for oxygen reduction reaction (ORR) activity by rotating disk electrode (RDE). NSTF-coated GC disks used in RDE experiments is a viable alternative to the regular mirror-polished GC disks in screening catalyst activities because both the catalytic activities and the effects of high-surface area support can be examined in a single measurement. The sputtered Pt-Ni samples have a much higher Surface Enhancement Factor (SEF) and kinetic current density. The impact of potential cycling is also included in this work.

RRDE Measurements of ORR Activity of Pt1-xIrx (0 < x < 0.3) on High Surface Area NSTF-coated GC Disks

Rotating (Ring) Disk Electrode (R(R)DE) experiments are commonly used to examine the kinetic activities of fuel cell (FC) catalysts with well-defined mass-transport properties [1]. Researchers at Dalhousie University regularly use RRDE as part of the screening process for potential FC catalyst candidates deposited by combinatorial sputtering techniques [2, 3]. In order to accurately determine the activities of sputtered catalysts that are enhanced by the high-surface area support, the glassy carbon discs were pre-coated with a layer of 3M’s high-surface area Nano-Structured Thin Film (NSTF) whiskers [4, 5]. The NSTF-coated GC discs have proven to be a viable alternative to the regular mirror-polished GC disks in screening catalysts activities because the material being measured has the same morphology, composition and surface structure as the material that would be used in a fuel cell [6].

Fine Tuning Highly Active Pt 3 Ni 7 Nanostructured Thin Films for Fuel Cell Cathodes

Polymer electrolyte membrane fuel cells (PEMFCs) are under intense research and development for transportation applications. It has been shown that a highly active, lower cost, oxygen reduction reaction (ORR) catalyst can be made by replacing a portion of the costly Pt catalyst with a transition metal, in this case Ni [1]. Further gains can be achieved through dealloying the PtNi alloy catalyst to create a Ptrich skin or shell, although spontaneous dealloying during fuel cell operation poses a significant durability issue [2]. While usually deployed in nanoparticle form, highly active Pt3Ni7 nanostructured thin films (NSTF) have also been demonstrated, and the substantial increase in both the specific activity and specific surface area has been attributed to a complex interplay between composition, grain size, lattice strain, and the catalyst nanoparticle morphology, e.g., Pt-skin, -shell or -skeleton structures [3].

A Combined Rotating Disk Electrode/X-ray Diffraction Study of Co Dissolution from Pt1-xCox Alloys

The oxygen reduction activity of a series of Pt1-xCox catalysts (with high Co content) sputter-deposited onto 3Ms nano-structured thin film support was measured with Rotating Disk electrode techniques. The activity was found to be much higher than that measured on Pt only. It was however not stable with repeated potential cycling. Ex-situ x-ray diffraction measurements of the disks during testing showed loss of bulk Pt from the lattice.