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

Abstract

Synthesis of bimetallic nanoparticles is a popular approach in developing novel electrocatalytic materials. In this work, by wet chemical protocols, we synthesized the mixed nickel–palladium nanocomposite on reduced graphene oxide support (Ni–Pd/rGO) alone with its monometallic analogues Ni/rGO and Pd/rGO as reference samples. The structure of the three nanocomposites was revealed by a set of advanced instrumental methods. In Ni/rGO, nickel evenly covers the rGO support in the form of single ions, chemically bound to the surface. In Pd/rGO, palladium is in form of nanoparticles with the size of 3–8 nm. In Ni–Pd/rGO, nickel uniformly covers the rGO surface, and Pd forms nanoparticles, similar to that in the monometallic analogues. At the same time, a thin surface layer of the Pd nanoparticles is enriched by Ni atoms. The nickel-enriched layer is not continuous, with a gradient of Ni content from the particle surface toward its center; its thickness does not exceed dimensions of two to three atomic layers. Only Pd/rGO and Ni–Pd/rGO demonstrated catalytic activity toward the hydrogen evolution reaction (HER), suggesting that catalytic properties stem from Pd, not Ni. Ni–Pd/rGO exhibits a significantly higher electrocatalytic surface area of 2.421 m2/g, compared to 0.278 m2/g for Pd/rGO, which could be explained by agglomeration of Pd nanoparticles in the latter and their lower availability to reagents. Both nanocomposites demonstrated good stability after 1000 cycles. Despite reduced palladium content, Ni–Pd/rGO demonstrated higher efficiency toward HER with overpotential of 63 mV compared to 116 mV for Pd/rGO: the catalytic efficiency is increased simultaneously with reducing the content of precious Pd by half. These observations can be explained by the alteration of the surface energy of the particles due to the difference in electronegativity and the lattice mismatch between the two metals.

Tuning the Electrocatalytic Activity of Pd Nanocatalyst toward Hydrogen Evolution and Carbon Dioxide Reduction Reactions by Nickel Incorporation

“…Powder X-ray diffraction studies of both Pd and NiPd show characteristic peaks corresponding to the Pd fcc crystal structure with Pd (111) being the most intense peak obtained in both cases (Figure 1a). 30 FESEM analysis of both Pd and NiPd shows an interconnected nano-network morphology (Figure S3). The bright-field TEM image (Figure 1b) of NiPd confirms the interconnected network morphology formed by the fusion of nanoparticles of size ∼5 nm.…”

“…ICP-OES analysis confirmed the presence of 7 wt % Ni in the NiPd catalyst. Powder X-ray diffraction studies of both Pd and NiPd show characteristic peaks corresponding to the Pd fcc crystal structure with Pd (111) being the most intense peak obtained in both cases (Figure a) …”

A Nickel-Doped Two-Dimensional Covalent Organic Polymer (2D-COP) for Electrocatalytic Hydrogen Evolution Reaction

“…In recent decades, there has been exploration into the development of platinum-free metal-based catalysts, such as transition metal oxides, carbides, , nitrides, sulfides, selenides, phosphides, , and hydroxides. , Unfortunately, many of these catalysts exhibit high onset overpotentials (η), Tafel slopes, and poor reliability. Consequently, research groups are actively developing catalysts employing metal-containing and metal-free materials and complexes as electro- and photocatalysts to reduce water to produce molecular hydrogen. − Parameters such as oxidation and reduction sites, redox potentials, and electronic structures play crucial roles in the development of more efficient catalysts for H 2 evolution. These catalysts improve electron transfer by lowering the energy gap, hence enhancing their catalytic performance.…”