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

Abstract

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 Cu₁Pd₁ nanospheres (NSs) with composition-graded (CG) structures (^CGCu₁Pd₁ NSs/C-HT); (2) through complete Cu underpotential deposition and Pt²⁺ galvanic replacement, the above-annealed ^CGCu₁Pd₁ NSs are further coated with Pt monolayer (ML) shells (MSs) (^CGCu₁Pd₁@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 ^CGCu₁Pd₁ NSs/C, commercial Pd/C and Pt/C, ^CGCu₁Pd₁ 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 ^CGCu₁Pd₁ core, ^CGCu₁Pd₁@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.