arXiv subjects

Alister J. Page

Publications and source records attributed to Alister J. Page.

3 recordsLinked to original sources

arXiv2025

Electronic Structure of Bimetallic CoRu Catalysts Modulates SWCNT Nucleation

Nucleation of single-walled carbon nanotubes (SWCNTs) via chemical vapour deposition of methane on CoRu bimetallic nanoparticles is simulated using quantum chemical molecular dynamics. By varying the Ru loading in the catalyst, we show that Ru decreases catalytic efficiency; C-H bond activation is impeded, key reactive intermediate species become longer-lived on the catalyst surface, and longer carbon chains are stabilised through the earliest stages of SWCNT nucleation. Analysis of the CoRu nanoparticle structure during the CVD process shows that this influence of Ru is indirect, with the catalyst adopting Ru-Co core-shell or segregated structures throughout nucleation, and Co exclusively driving the catalytic decomposition of the methane precursor. We show that the influence of Ru occurs via the electronic structure of the catalyst itself, by lowering the Fermi level of the catalyst due to lower energy 4d/5s states, in a manner consistent with d-band theory.

cond-mat.mtrl-sci↗

arXiv2025

How oxygen influences the catalytic activity of iron during carbon nanotube nucleation

The catalytic activity of metal nanoparticles toward nucleation of single-walled carbon nanotubes (SWCNTs) is fundamental to achieving structure-controlled growth using catalytic chemical vapor deposition (CVD). Despite the success of oxidized catalysts in SWCNT growth, there is a lack of understanding regarding how oxygen influences the catalysts and the nucleation process. Quantum chemical molecular dynamics (MD) simulations employing density functional tight binding (DFTB) demonstrate that the kinetics of carbon nucleation on an iron nanoparticle catalyst can be tuned via oxygen loading. Increasing the oxygen content in the catalyst leads to activation of surface-bound carbon species and enhanced carbon chain growth due to respective weakening and strengthening of the C-C and Fe-C bonding. This is due to oxygen modulating the electronic structure of the iron catalyst, with the Fermi level of the catalyst increasing proportionally with oxygen content until the iron:oxygen stoichiometry reaches parity. The increase in Fe 3d states near the Fermi level also promotes the donation of electron density into unoccupied C 2p states, activating C-C bonds which in turn facilitates carbon chain growth and slows carbon ring condensation.

cond-mat.mtrl-sci↗

arXiv2025

There is Nothing Anomalous about 'Anomalous' Underscreening in Concentrated Electrolytes

Over the last decade, experimental measurements of electrostatic screening lengths in concentrated electrolytes have exceeded theoretical predictions by orders of magnitude. This disagreement has led to a paradigm in which such screening lengths are referred to as 'anomalous underscreening', while moderate screening lengths - predominantly those predicted by theory and molecular simulation - are referred to as 'normal underscreening'. Herein we use discrete Fourier analysis of the radial charge density obtained from molecular dynamics simulations to confirm the presence of many electrostatic screening modes present at any one time. We present a new approach for extracting screening lengths directly from the bulk charge density that reveals the origins of both normal and anomalous underscreening. These results reconcile a decades-old disagreement between experimental measurements and theoretical predictions of screening lengths in concentrated electrolytes.

cond-mat.soft↗