Extended Surface Electrocatalysts Synthesized Via Atomic Layer Deposition

Platinum-nickel nanowires are a promising advanced catalyst material for the oxygen reduction reaction (ORR) in fuel cell applications. When synthesized by galvanic displacement of nickel nanowires (NiNWs), these extended surface electrocatalysts have demonstrated activity and durability superior to benchmark carbon-supported Pt nanoparticle catalysts. However, challenges in scale-up and reproducibility of this fabrication process have prompted investigation into alternative synthesis routes. In this work, atomic layer deposition (ALD) of Pt was used to develop a scalable analog process to the galvanic displacement of extended surface electrocatalyts. Pt was deposited on nickel nanowire substrates in packed bed reactor equipped with in situ mass spectrometry to monitor products of the ALD half-reactions. The ALD process was investigated using both O₂ and H₂ as ligand removal agents. Resulting PtNi nanowire catalysts were characterized at 5, 10, 20, and 30 cycles of ALD using a variety of analytical techniques (chemisorption, ICP-MS, electron microscopy) to analyze the nucleation and growth of the Pt during the deposition process and its effects on active surface area. In the case of the oxidative ALD process, these novel extended surface catalysts were found to possess an ORR mass activity almost 3X higher than benchmark Pt/C and over 70% retention of activity after durability testing.