Volume 44: Energy Transitions toward Carbon Neutrality: Part VII

Detrimental 2p-3d Hybridisation in Ni Nanosheets Supported on Strontium Dioxide for Catalytic H2 Production, Necessitating Thickness Optimisation Kabir S. Suraj , M. Hussein N. Assadi

Abstract

We employ accurate density functional theory
calculations to examine the electronic structure of three
Ni/SrO2 nanostructures containing single-layer, bilayer
and four-layer Ni nanosheets. The single Ni layer
interacts strongly with the topmost oxygen layer at the
Ni/SrO2 interface, resulting in significant surface
reconstruction and strong hybridisation between the O
2p and Ni 3d states. For the bilayer Ni, the layer facing
the interface also strongly interacts with the O. However,
the second layer retains its geometry. For the four-layer
system, none of the Ni layers interacted strongly with O.
According to the electronic population analysis, in the
thinnest nanosheets, the strong hybridisation with
oxygen pulls Ni’s 3d states away from the Fermi level
deeper into the valence band. In these cases, Ni’s
electronic population that is labile for catalysis in the
vicinity of the Fermi level was as little as half of the
bilayer nanosheet. Such reduction in the labile 3d
population has a detrimental effect on Ni’s catalytic
performance in de-hydrogenating formic acid. Our
results demonstrate that there is an optimum dimension
for Ni nanoparticles below or above which the catalytic
performance deteriorates. Consequently, reducing the
Ni dimension to maximise the surface in the hope of
better catalytic yield might not be the best strategy as
detrimental p-d hybridisation takes hold. Smaller might
not always be better after all!

Keywords strontium dioxide, nickel, catalytic hydrogen production, density functional theory, interface