Core–Shell Pd@M (M=Ni, Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction

Herein, it is demonstrated that pyrene butyric acid (PBA)‐stabilized metal nanoparticles with core–shell morphology, Pd@MNPs (M=Ni, Cu, Co), non‐covalently supported on graphene (G) sheets, are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading. The PBA‐stabilized Pd@MNPs (M=Ni, Cu, Co)/G ensembles were prepared by employing a simple modified polyol method and galvanic replacement and thoroughly characterized with advanced microscopy imaging and complementary spectroscopic techniques. Electrochemical studies revealed that Pd@NiNPs/G presents the optimum performance, exhibiting a 30 mV more positive onset potential and 3.2 times greater mass activity over Pd/C. Moreover, chronoamperometric assays showed the minimum activity loss for Pd@NiNPs/G, not only among its core–shell counterparts but importantly when compared with the benchmark catalyst. The excellent performance of Pd@NiNPs/G was attributed to the (a) presence of PBA as stabilizer, (b) uniform Pd@NiNPs dispersion onto the graphene sheets, (c) efficient intra‐ensemble interactions between the two species, (d) existence of the core–shell structure for Pd@NiNPs, and (e) stability of the Ni core metal under the reaction conditions. Last, the oxygen reduction on Pd@NiNPs/graphene occurs by the direct four‐electron reduction pathway, showing great potential for use in energy related applications. Nickel ensembles: Pyrene butyric acid (PBA)‐stabilized metal nanoparticles with core–shell morphology, Pd@MNPs (M=Ni, Cu, Co), non‐covalently supported on graphene (G) sheets are presented. The Ni‐based ensembles are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading.