Increasing Durability of Fuel Cell Catalysts with Atomic Layer Deposition

The proton exchange membrane (PEM) fuel cell is a highly efficient, portable, non-greenhouse gas emitting source of electrical power that holds great promise as a replacement for the internal combustion engine. One of the most significant challenges in the development 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 of the Pt nanoparticle catalyst and degradation of the carbon support. In this work, atomic layer deposition (ALD) was used to produce both modified Pt nanoparticle catalysts as well as PtNi extended surface catalysts with enhanced electrochemical durability. Commercial and ALD-synthesized (on functionalized carbon black) Pt/C catalysts were modified with TiO₂ ALD to create protective nanostructures on the support surface that acted as physical barriers to Pt agglomeration and preserved electrochemical surface area and mass activity over voltage cycling. Extended surface catalysts synthesized by galvanic displacement have previously been shown to have high activity and enhanced durability over Pt/C catalysts due to highly-coordinated surface Pt and elimination of the carbon support. An analog of the galvanic displacement process was developed using Pt ALD on Ni nanowires substrates to create a novel extended surface catalyst with mass activity almost 3X higher than benchmark Pt/C and over 70% retention of activity after durability testing. The PtNi nanowire catalysts were characterized at 5, 10, 20, and 30 cycles of ALD to analyze the nucleation and growth of the Pt during the deposition process and its effects on active surface area.