MOF-derived PtCo/Co3O4 nanocomposites in carbonaceous matrices as high-performance ORR electrocatalysts synthesized via laser ablation techniques

Abstract

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. Herein, we present our recently patented tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) as a facile technique for the synthesis of Pt–Co bimetallic nanoparticles encapsulated in the simultaneously formed metal organic frameworks (MOF) phases of ZIF-67 out of the laser ablation process. Upon pyrolytic post-treatments, these 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. We investigate the effect of the Pt precursor (K₂PtCl₄) concentrations during the LASiS-GRR technique in facilitating a higher degree of Pt–Co alloying in the phases as the K₂PtCl₄ initial concentrations are increased from 65 to 125 mg L⁻¹. Our results from subsequent electrochemical characterizations reveal the ability of the as-manufactured NCs in the carbonaceous matrix to exhibit superior electrocatalytic activities towards oxygen reduction reaction (ORR) while maintaining their long-term stabilities in a highly concentrated alkaline media (KOH 1 M). Specifically, the NCs synthesized from a 125 mg L⁻¹ K₂PtCl₄ solution demonstrated 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.