(282d) Particle Atomic Layer Deposition for Stabilization of Oxygen Reduction Catalysts

As a highly efficient, portable, non-greenhouse gas emitting source of electrical power, the proton exchange membrane (PEM) fuel cell holds great potential as a replacement for the internal combustion engine. One of the most significant development challenges in the commercialization of the PEM fuel cell is the long-term durability of the oxygen reduction reaction (ORR) catalyst. Cathode potential cycling—resulting from the variable voltage loads imposed during vehicular operation—is known to promote agglomeration and growth of the Pt nanoparticle catalyst, which in turn degrades the power output of the fuel cell. In this work, atomic layer deposition (ALD) was used to deposit protective TiO₂ films onto both commercial and ALD-synthesized Pt/C catalyst in order to increase its electrochemical durability. Deposition half-reactions during fluidized bed particle ALD were observed via in-situ mass spectrometry, and chemisorption analysis was used to quantify changes in Pt surface area following TiO₂ deposition. Rotating disk electrode analysis indicated that electrochemical surface area (ECSA) and activity were slightly depressed by the addition of TiO₂ ALD layers. Activity retention during electrochemical durability testing was modestly improved, with TiO₂-coated catalysts retaining upwards of 60% of their initial activity. Examination of catalysts before and after testing also showed that TiO₂ ALD barriers were effective at preventing Pt agglomeration under fuel cell operating conditions. Further testing of the catalysts in membrane electrode assemblies was used to quantify effects of TiO₂ ALD on the hydrophobicity of the catalysts, which has been previously demonstrated as an important factor in fuel cell device operation with ALD-fabricated catalysts.