Ni-Pd Nanocomposites on Reduced Graphene Oxide Support as Electrocatalysts for Hydrogen Evolution Reactions

Synthesis of bimetallic nanoparticles is a popular approachindeveloping novel electrocatalytic materials. In this work, by wetchemical protocols, we synthesized the mixed nickel-palladiumnanocomposite on reduced graphene oxide support (Ni-Pd/rGO)alone with its monometallic analogues Ni/rGO and Pd/rGO as referencesamples. The structure of the three nanocomposites was revealed bya set of advanced instrumental methods. In Ni/rGO, nickel evenly coversthe rGO support in the form of single ions, chemically bound to thesurface. In Pd/rGO, palladium is in form of nanoparticles with thesize of 3-8 nm. In Ni-Pd/rGO, nickel uniformly coversthe rGO surface, and Pd forms nanoparticles, similar to that in themonometallic analogues. At the same time, a thin surface layer ofthe Pd nanoparticles is enriched by Ni atoms. The nickel-enrichedlayer is not continuous, with a gradient of Ni content from the particlesurface toward its center; its thickness does not exceed dimensionsof two to three atomic layers. Only Pd/rGO and Ni-Pd/rGO demonstratedcatalytic activity toward the hydrogen evolution reaction (HER), suggestingthat catalytic properties stem from Pd, not Ni. Ni-Pd/rGO exhibitsa significantly higher electrocatalytic surface area of 2.421 m(2)/g, compared to 0.278 m(2)/g for Pd/rGO, which couldbe explained by agglomeration of Pd nanoparticles in the latter andtheir lower availability to reagents. Both nanocomposites demonstratedgood stability after 1000 cycles. Despite reduced palladium content,Ni-Pd/rGO demonstrated higher efficiency toward HER with overpotentialof 63 mV compared to 116 mV for Pd/rGO: the catalytic efficiency isincreased simultaneously with reducing the content of precious Pdby half. These observations can be explained by the alteration ofthe surface energy of the particles due to the difference in electronegativityand the lattice mismatch between the two metals.

Automated summary

In this study, a mixed nickel-palladium nanocomposite was synthesized using wet chemical methods, and compared with monometallic analogues Ni/rGO and Pd/rGO. Advanced instrumental methods revealed the structure of the three nanocomposites. The Ni-Pd/rGO exhibited higher electrocatalytic surface area and catalytic activity, indicating that its catalytic properties mainly stem from palladium.