(282a) Rational Design and Synthesis of Surfactant-Free Pt-Based Ternary Nanoalloys As Superior Oxygen Reduction Reaction Electrocatalysts

Efficient and low cost electrocatalysts are indispensable for electrochemical oxygen reduction reactions (ORR) during proton exchange membrane fuel cell (PEMFC) operations. Yet, the challenge for solution phase synthesis of nanocatalysts with low precious metal loading, high durability and catalytic activities remains in tailoring their architectures and compositions without using unwanted chemicals and surfactants/ligands that are known to impede their active catalytic sites. We present to synthesize ternary nanoalloys (NAs) of Pt with transition metals (Co, Cu, Ni, Ti, Ru, Mn) as ORR electrocatalysts using our recently developed laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) technique as a facile and surfactant-free nanomanufacturing route. The specific choice of the elemental compositions is driven by the respective target metal/metal salt redox potential gaps as well as the target metal and/or, metal oxide solubility in desired acids. The high-energy thermodynamics of the LASiS-GRR process enables control of the sizes, elemental compositions and distributions of the ternary NAs through systematic tuning of initial metal salt concentration, pH, laser fluence and ablation time. Specifically, the PtCuCo NAs synthesized with an elemental composition of 72:12:16 (Pt:Co:Cu) indicates the best ORR catalytic activity. The NAs largely possess shell-core structure with the shell comprising mostly of Pt and minor amount Cu, along with a uniformly alloyed PtCuCo core. Mass and specific activities for ORR performance of the NAs indicate a 4 and 6.5-fold improvements respectively over the corresponding activities of commercial Pt/C. We attribute the enhanced activity to 1) our surfactant/ligand-free synthesis technique that prevents catalytic site degradations; and 2) minor alloying of the second transition metal Cu that shifts back the Pt d-band center to an optimal position between that of Pt and the PtCo binary NAs, thereby tuning their binding affinities for both oxygen and oxygenated species. Finally, this work establishes the versatility of the LASiS-GRR technique through the synthesis of other ternary NAs (PtRuNi, PtCoMn, PtNiTi) that also exhibit reasonably good ORR activities.