Downshift of the Ni d band center over Ni nanoparticles confined within an amorphous silicon nitride matrix

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 53; no. 12; pp. 5686 - 5694
• Main Authors: Asakuma, Norifumi, Tada, Shotaro, Tamura, Tomoyuki, Kawaguchi, Erika, Honda, Sawao, Asaka, Toru, Bouzid, Assil, Bernard, Samuel, Iwamoto, Yuji
• Format: Journal Article
• Published: 19.03.2024
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d3dt04155g

Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si 3 N 4 ) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO 2 ) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H 2 )-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H 2 desorption at about 100-130 °C evaluated for the Ni/a-Si 3 N 4 sample (47.4 kJ mol −1 ) was lower than that for the Ni/a-SiO 2 sample (68.0 kJ mol −1 ). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si 3 N 4 matrix compared to O atoms in the a-SiO 2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H 2 desorption, as experimentally observed in the Ni/a-Si 3 N 4 sample. More covalent Ni-N bonds at Ni/amorphous Si 3 N 4 heterointerfaces resulted in downshifting the Ni d band centerand facilitating H 2 desorption.