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Stanford, VW researchers use ALD to build OER electrodes for high-power-density fuel cells

A team from Stanford University and Volkswagen Group Research in Wolfsburg, with colleagues from McMaster University in Canada, the University of Delaware, SINTEF and the Norwegian University of Science and Technology have used an atomic layer deposition-facilitated electrode fabrication technique to build electrodes for the oxygen reduction reaction (ORR) in high-power-density PEM fuel cells.

In a paper published in the journal Cell Reports Physical Science, the researchers report that the combination of an agglomerated ionomer dispersion and a mesoporous support gives access to a high catalytic activity (mass activity [MA] = 0.31 A/mgPt with pure Pt) that can be maintained at high current densities.

Dull

Dull et al.


They hypothesized that the formulation results in Pt sufficiently withdrawn from the ionomer such that poisoning and transport losses are reduced. When paired with a low-resistance dispersion-cast membrane, a 0.1-mgPt/cm2 cathode can deliver a 0.65-V power density of 1.0 W/cm2 at 150 kPa and 80 ˚C. The assembly also demonstrates impressive durability, losing only 33 mV after 30,000 cycles.

Enabling fast refueling and long ranges, hydrogen (H2)-powered proton exchange membrane fuel cells (PEMFC) are emerging alongside lithium (Li)-based batteries as a reduced-emission alternative to internal combustion engines (ICEs) for transportation applications. To lower costs and support the deep market penetration of PEMFC vehicles, automotive manufacturers are interested in decreasing the quantity of platinum (Pt) in the electrodes.

… Because of the rapid H oxidation kinetics on Pt catalysts, anode loadings as low as 0.025 mgPt/cm2 can be used in PEMFCs without considerable voltage loss. This leaves a target of <0.1 mgPt/cm2 for the cathode to achieve the rated power density of 1 W/cm2 at a reasonable cell efficiency. Due to sluggish oxygen (O2) reduction reaction (ORR) kinetics and the relatively dilute presence of O2 in air, this presents a major challenge. To improve ORR kinetics, a large body of important work has gone into improving the intrinsic activity of Pt, largely through alloying and nanostructuring. Although order-of-magnitude improvements have been made in mass-normalized activity relative to Pt in the rotating disk electrode test configuration, translating these improvements into industrially relevant membrane electrode assemblies (MEAs) has remained a challenge.

… Here, we introduce an MEA fabrication technique facilitated by atomic layer deposition in which carbon (C), Pt, and ionomer are deposited sequentially. Unconstrained by the need to disperse an ink, we can tune the ionomer solvent environment independently of the Pt/C nanostructure. In evaluating a series of ionomer dispersion alcohol contents and carbon supports, we found that the combination of agglomerated ionomer dispersions and mesoporous furnace C yielded remarkably active cathodes at both low current densities (LCDs) and HCDs.

—Dull et al.

Resources

  • Dull et al. (2020) “Bottom-Up Fabrication of Oxygen Reduction Electrodes with Atomic Layer Deposition for High-Power-Density PEMFCs,” Cell Reports Physical Science doi: 10.1016/j.xcrp.2020.100297

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