Size Sensitivity of Supported Palladium Species on Layered Double Hydroxides for the Electro-oxidation Dehydrogenation of Hydrazine: From Nanoparticles to Nanoclusters and Single Atoms
Guihao Liu, Tianqi Nie, Huijuan Wang, Tianyang Shen, Xiaoliang Sun, Sha Bai, Lirong Zheng, Yu‐Fei Song
Abstract
The hydrazine oxidation reaction (HzOR) is structure-sensitive, and a slight modification of the catalyst structure can generate a significant change in activity. To date, no study on the size effect of the catalyst at a subnanometer scale on HzOR has been reported yet. Herein, we report the fabrication of Pd species with sizes ranging from nanoparticles (NPs) and nanoclusters (NCs) to single atoms (SAs) onto a NiFe-layered double hydroxide by fine-tuning precursors and reduction methods. When applied for the electro-oxidation dehydrogenation of hydrazine, the as-prepared Pd NCs/NiFe exhibit a current density of 4.3 A mgPd–1 at 0.35 V versus RHE. It should be noted that the mass activity of Pd NCs/NiFe was 36 times that of Pd SAs/NiFe and 7 times that of Pd NPs/NiFe, respectively. The in situ electrochemical impedance spectroscopy and density functional theory calculation demonstrate that different from previous studies, both the Pd SAs/NiFe and Pd NPs/NiFe are suboptimal in HzOR due to the isolated active sites of the Pd SAs/NiFe and large steric hindrance of Pd NPs/NiFe, respectively. Instead, the strong intracluster interactions of Pd NCs/NiFe lift the d-band center closer to the Fermi level, leading to stronger hybridization of Pd d-orbitals and the σ orbitals of N2H4 molecules. Consequently, the excellent performance of Pd NCs/NiFe can be attributed to its multiple neighboring metal sites, high d-band center, and small steric hindrance.