(630b) Extended Surface Electrocatalyst Development Via Atomic Layer Deposition

Extended surface electrocatalysts based on nanowire templates have emerged as promising candidates for advanced catalysts for the oxygen reduction reaction (ORR) in fuel cell applications. When synthesized by spontaneous galvanic displacement (SGD) of nickel nanowires (NiNWs), these extended surface electrocatalysts have demonstrated exceptional performance (specific activity > 6000 μA/cm²) and superior durability to benchmark carbon-supported Pt catalysts. However, challenges in scale-up and reproducibility of this fabrication process have prompted an investigation into atomic layer deposition (ALD) as a facile, scalable synthesis alternative for the production of extended thin film electrocatalyst structures. An ALD analog of the SGD synthesis process was developed using an oxidative Pt ALD chemistry in a viscous flow reactor. In situ mass spectrometry was used to study the deposition reactions, while elemental analysis, transmission electron microscopy, elemental mapping and X-ray diffraction were used to characterize Pt growth and effects of post-treatment procedures, such as H₂ annealing. Electrochemical half-cell testing showed that the highest-performing ALD catalyst was 16 times more active than commercial Pt/C. After integration into membrane electrode assemblies, these materials were also found to exceed the DOE 2020 mass activity target of 440 mA/mg_Pt. Further work is also underway to leverage the tunable nature of ALD to develop a co-deposition process with Pt and Ni ALD on a cobalt nanowire (CoNW) substrate. Fabrication of these trimetallic extended surface catalysts using ALD “supercycles” and subsequent characterization experiments will also be discussed.