Ljiljana Atanasoska

Surface injection catalysis at glassy carbon electrodes

Injection of solution species into glassy carbon electrodes has been monitored by Phase Detection Microscopy (PDM), and by sputter profiling and surface analysis. Electrochemical treatment in strongly alkaline solutions at positive voltage conditions caused swelling of the surface at local spots and eventual disruption of the surface with the formation of pits. The number, size, and depth of the pits increased with increased voltage. X-ray Photoelectron Spectroscopy (XPS) depth profiles revealed the presence of oxygen species below the surface at depths that were dependent on electrochemical treatment. Increased positive voltage or increased treatment time gave surfaces with oxygen at greater depths below the surface. Glassy carbon, activated as described here, has been found to support a high rate oxidation of S2− to polysulfides.

Efficient Oxygen Evolution Reaction Catalysts for Cell Reversal and Start/Stop Tolerance

Minute amounts of ruthenium and iridium on platinum nanostructured thin films have been evaluated in an effort to reduce carbon corrosion and Pt dissolution during transient conditions in proton exchange membrane fuel cells. Electrochemical tests showed the catalysts had a remarkable oxygen evolution reaction (OER) activity, even greater than that of bulk, metallic thin films. Stability tests within a fuel cell environment showed that rapid Ru dissolution could be managed with the addition of Ir. Membrane electrode assemblies containing a Ru to Ir atomic ratio of 1:9 were evaluated under start-up/shutdown and cell reversal conditions for OER catalyst loadings ranging from 1 to 10 μg/cm2. These tests affirmed that electrode potentials can be controlled through the addition of OER catalysts without impacting the oxygen reduction reaction on the cathode or the hydrogen oxidation reaction on the anode. The morphology and chemical structure of the thin OER layers were characterized by scanning transmission electron microscopy and X-ray photoelectron spectroscopy in an effort to establish a correlation between interfacial properties and electrochemical behavior.

Development of Catalysts with Enhanced Tolerance to Fuel Cell Transient Conditions

A Ru1-xIrx binary over-layer was deposited on Pt-coated nano-structured thin film from 3M Company. XPS measurements were used to confirm the composition of the over-layer. Rotating disk electrode measurements were used to assess oxygen evolution activity of the catalysts. The results showed that a low Ir/high Ru over-layer had a higher activity but lower stability than high Ir/low Ru samples.

Final Report - Durable Catalysts for Fuel Cell Protection during Transient Conditions

The objective of this project was to develop catalysts that will enable proton exchange membranes (PEM) fuel cell systems to weather the damaging conditions in the fuel cell at voltages beyond the thermodynamic stability of water during the transient periods of start-up/shut-down and fuel starvation. Such catalysts are required to make it possible for the fuel cell to satisfy the 2015 DOE targets for performance and durability. The project addressed a key issue of importance for successful transition of PEM fuel cell technology from development to pre-commercial phase. This issue is the failure of the catalyst and the other thermodynamically unstable membrane electrode assembly (MEA) components during start-up/shut-down and local fuel starvation at the anode, commonly referred to as transient conditions. During these periods the electrodes can reach potentials higher than the usual 1.23V upper limit during normal operation. The most logical way to minimize the damage from such transient events is to minimize the potential seen by the electrodes. At lower positive potentials, increased stability of the catalysts themselves and reduced degradation of the other MEA components is expected.