Promoting Effects of Au Submonolayer Shells on Structure-Designed Cu-Pd/Ir Nanospheres: Greatly Enhanced Activity and Durability for Alkaline Ethanol Electro-Oxidation

Rationally engineering the surface physicochemical properties of nanomaterials can improve their activity and durability for various electrocatalytic and energy conversion applications. Cu-Pd/Ir (CPI) nanospheres (NSs) anchored on N-doped porous graphene (NPG) [(CPI NSs/NPG)] have been recently demonstrated as a promising electrocatalyst for the alkaline ethanol oxidation reaction (EOR); to further enhance their electrocatalytic performance, the NPG-supported CPI NSs are coated with Au submonolayer (SML) shells (SMSs), through which their surface physicochemical properties can be tuned. CPI NSs/NPG is prepared by our previously developed method and possesses the special structures of composition-graded Cu1Pd1 and surface-doped Ir-0.03. The Au SMSs with designed surface coverages are formed via an electrochemical technology involving incomplete Cu underpotential deposition (UPD) and Au3+ galvanic replacement. A distinctive volcano-type relation between the EOR electrocatalytic activity and the Au-SMS surface coverage for CPI@Au-SML NSs/NPG is revealed, and the optimal CPI@Au-1/6ML NSs/NPG greatly surpasses commercial Pd/C and CPI NSs/NPG in electrocatalytic activity and noble metal utilization. More importantly, its electrocatalytic durability in 1 h chronoamperometric and 500-cycle potential cycling degradation tests is also significantly improved. According to detailed physicochemical characterizations, electrochemical analyses, and density functional theory calculations, the promoting effects of the Au SMS for enhancing the EOR electrocatalytic activity and durability of CPI NSs/NPG can be mainly attributed to the greatly weakened carbonaceous intermediate bonding and properly increased surface oxidation potential. This work also proposes a versatile and effective strategy to tune the surface physicochemical properties of metal-based nanomaterials via incomplete UPD and metal-cation galvanic replacement for advancing their electrocatalytic and energy conversion performance.