Abstract
We present a systematic first-principles density functional theory study with dispersion corrections (DFT-D3) of hydrazine adsorption on the experimentally observed (111), (110) and (100) surfaces of the binary β1-NiZn alloy. A direct comparison has been drawn between the bimetallic and monometallic Ni and Zn counterparts to understand the synergistic effect of alloy formation. The hydrazine adsorption mechanism has been characterised through adsorption energies, Bader charges, the d-band centre model, and the coordination number of the active site - which is found to dictate the strength of the adsorbate–surface interaction. The bimetallic β1-NiZn nanocatalyst is found to exhibit higher activity towards adsorption and activation of hydrazine compared to the monometallic Ni and Zn counterparts. The Ni-sites of the bimetallic NiZn surfaces are found to be generally more reactive than Zn sites, which is suggested to be due to the higher d-band centre of −0.13 eV (closer to the Fermi level), forming higher energy anti-bonding states through NiN interactions. The observed synergistic effects derived from surface composition and electronic structure modification from Ni and Zn alloying should provide new possibilities for the rational design and development of low-cost bimetallic Ni-Zn alloy catalysts for direct hydrazine fuel cell (DHFC) applications.
Highlights
With the depletion of conventional energy sources and the growing need for energy in society, coupled with the challenge to ameliorate climate change, the development and improvement of safe, renewable, and low-cost clean energy technologies are necessary
The (1 1 0) surface is terminated by Ni:Zn in a 1:1 ratio, with the Ni and Zn atoms in an 8-fold coordination number (CN)
These results suggest that the combination of two weakly active metals (Ni and Zn) gives a highly active bimetallic NiZn catalyst for hydrazine adsorption and activation towards direct hydrazine fuel cell applications
Summary
With the depletion of conventional energy sources and the growing need for energy in society, coupled with the challenge to ameliorate climate change, the development and improvement of safe, renewable, and low-cost clean energy technologies are necessary. Promising non-noble bimetallic catalysts for DHFC’s include alloys with other first row transition metals, such as Ni-Cu, [23] Ni-Fe, [24] and Ni-Zn [25,26]. DFT-based calculations have been employed extensively to predict the adsorption geometries of hydrazine on metallic surfaces and offers good insight into catalyst activity [24,32,33]. Dispersion-corrected DFT-D3 calculations are employed to comprehensively investigate the adsorption properties of hydrazine on the bimetallic β1-NiZn alloy catalyst (1 0 0), (1 1 0), and (1 1 1) surfaces. The energetics and structural parameters of the lowest-energy adsorption configurations of the hydrazine are presented and a d-band model was developed to gain insight into the differences in reactivity of the bimetallic catalyst compared to the monometallic counterparts. Differential charge density iso-surface contour and projected density of states analyses were carried out to gain further atomic-level insights into the hydrazine adsorption mechanism
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