Probing structure-designed Cu-Pd nanospheres and their Pt-monolayer-shell derivatives as high-performance electrocatalysts for alkaline and acidic oxygen reduction reactions

The oxygen reduction reaction (ORR) plays a critical role in various renewable energy technologies, however, the unsatisfactory ORR electrocatalytic performance of commonly used commercial electrocatalysts under alkaline and acidic conditions greatly limits the wide practical applications of these technologies. Accordingly, in this study, (1) a facile heat treatment (HT) is exploited to anneal carbon-supported highly uniform and small-sized Cu 1 Pd 1 nanospheres (NSs) with composition-graded (CG) structures ( CG Cu 1 Pd 1 NSs/C-HT); (2) through complete Cu underpotential deposition and Pt 2+ galvanic replacement, the above-annealed CG Cu 1 Pd 1 NSs are further coated with Pt monolayer (ML) shells (MSs) ( CG Cu 1 Pd 1 @Pt ML NSs/C-HT). Detailed physicochemical characterization, electrochemical analyses and density functional theory calculations reveal that, benefiting from the CG structural, size-morphology and annealing effects of the NSs, as well as the Cu-induced geometric and ligand effects, compared to CG Cu 1 Pd 1 NSs/C, commercial Pd/C and Pt/C, CG Cu 1 Pd 1 NSs/C-HT exhibits not only ultrahigh alkaline ORR electrocatalytic activity, showing respective 1.1/1.2-, 4.7/13.7- and 5.2/6.8-fold enhancements in area-/noble-metal-mass-specific activity (ASA/NM-MSA), but also a satisfactory alkaline electrochemical durability. Besides, owing to the Pt-MS structural effect and the synergistic effect on the Pt MS imparted by the CG Cu 1 Pd 1 core, CG Cu 1 Pd 1 @Pt ML NSs/C-HT presents remarkable acidic ORR electrocatalytic activity, NM utilization and acidic electrochemical durability compared to commercial Pt/C, exhibiting respective 3.4-, 3.4- and 13.3-fold enhancements in ASA, NM-MSA and Pt-MSA. This study has not only successfully developed two types of high-performance ORR electrocatalyst, but also comprehensively investigated the origins of their significantly enhanced ORR electrocatalytic performance for the rational design and preparation of highly active and durable ORR electrocatalysts. Composition-graded Cu-Pd nanospheres are annealed for highly efficient alkaline oxygen reduction reaction, and further coated with Pt monolayer shells for high-performance acidic oxygen reduction reaction.