(140c) MOF-Derived PtCo/Co3O4 nanocomposites in Carbonaceous Matrices As High-Performance ORR Electrocatalysts Synthesized Via laser Ablation Techniques

Rapidly expanding global energy demands due to fast-paced human-technology interfaces have propelled fuel cell technology as a sustainable energy-conversion alternative. Nonetheless, the rational development of such technology demands the engineering of low-cost durable materials that can exhibit and retain specific electrocatalytic activities to sustain the electrochemical energy conversions. Over the years, our group has extensively developed the now-patented laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) technique as a non-equilibrium, one-pot and green route for synthesizing disparate heteronanostructured intermetallic composites^1,2 including Metal Organic Frameworks (MOF)³ without using any surfactants/ligands, that can be tuned for diverse interfacial activities (energetics, optical, electrochemical). Herein, we specifically present LASiS-GRR as a facile route for the synthesis of Pt-Co bimetallic nanoparticles (NPs) encapsulated in MOF phases of ZIF-67 that are concurrently formed during the laser ablation process.⁴ Upon pyrolytic post-treatments, these composite structures are found to be partially altered, giving rise to the formation of graphitic shell coated Pt-Co bimetallic nanocomposites (NCs) that are spatially framed onto Co₃O₄-decorated carbonaceous matrices. Our investigations into the effects of Pt precursor (K₂PtCl₄) concentrations during the LASiS-GRR technique indicate that increasing K₂PtCl₄ initial concentrations in the solution-phase facilitate a higher degree of Pt-Co alloying. Subsequent electrochemical characterizations reveal the ability of these hybrid NCs in carbonaceous matrices to exhibit superior electrocatalytic activities towards oxygen reduction reaction (ORR) while maintaining long-term stability in highly concentrated alkaline media (KOH 1M). Specifically, the NCs synthesized from LASiS under 125 mg·L^-1 K₂PtCl₄ solution,demonstrate an extraordinary 5-fold enhancement in their specific mass activities as compared to state-of-the-art commercial Pt catalysts. These outstanding performances are attributed to the unique configurations arising from cooperative catalytic activities (spill-over effects) between the graphitic shell coated bimetallic Pt-Co nanoparticles and the electrochemically active Co₃O₄-decorated carbon matrix support.

References:

1. Hu S, Goenaga G, Melton C, Zawodzinski TA, Mukherjee D. PtCo/CoOx nanocomposites: Bifunctional electrocatalysts for oxygen reduction and evolution reactions synthesized via tandem laser ablation synthesis in solution-galvanic replacement reactions. Applied Catalysis B: Environmental. 2016;182:286-296.
2. Hu S, Tian M, Ribeiro EL, Duscher G, Mukherjee D. Tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) for the production of PtCo nanoalloys as oxygen reduction electrocatalysts. Journal of Power Sources. 2016;306:413-423.
3. Ribeiro EL, Davari SA, Hu S, Mukherjee D, Khomami B. Laser-induced synthesis of ZIF-67: a facile approach for the fabrication of crystalline MOFs with tailored size and geometry. Materials Chemistry Frontiers. 2019;3(7):1302-1309.
4. Ribeiro EL, Davis EM, Mokhtarnejad M, Hu S, Mukherjee D, Khomami B. MOF-derived PtCo/Co3O4 nanocomposites in carbonaceous matrices as high-performance ORR electrocatalysts synthesized via laser ablation techniques. Catalysis Science & Technology. 2021.