Two-dimensional Iron Monocarbide with Planar Hypercoordinate Iron and Carbon

TL;DR

This paper reports the theoretical discovery of stable two-dimensional iron monocarbide sheets with unique planar hypercoordinate structures, potential for high-capacity energy storage, and superconductivity at low temperatures.

Contribution

It introduces two novel 2D iron monocarbide structures with unprecedented hypercoordinate configurations and explores their stability, electrochemical properties, and superconducting potential.

Findings

t-FeC is the global minimum configuration among the studied structures.

t-FeC can stably adsorb lithium with high capacity and low diffusion barrier.

t-FeC shows potential as a 2D superconductor with a transition temperature of 6.77 K.

Abstract

We report on the theoretical discovery of Iron monocarbide binary sheets stabilized at two-dimensional confined space, which we call tetragonal-FeC (t-FeC) and orthorhombic-FeC (o-FeC), respectively. From the energy viewpoint, the proposed t-FeC is the global minimum configuration in the 2D space, and each carbon atom is four-coordinated with ambient four Iron atoms. Strikingly, the o-FeC monolayer is an orthorhombic phase with planar pentacoordinate carbon moiety and planar seven-coordinate Fe moiety. To our knowledge, this monolayer is the first example of a simultaneously pentacoordinate carbon and planar seven-coordinate Fe-containing material. State-of-the-art theoretical calculations confirm that all these monolayers have significantly dynamic, mechanical, and thermal stabilities. Among these two monolayers, t-FeC monolayer shows a higher theoretical capacity (395 mAh g-1 ), and can stably adsorb Li up to t-FeCLi3 . Low migration energy barrier is predicted as small as 0.26 eV for Li, which result in the fast diffusion of Li atom on this monolayer. Moreover, electron-phonon calculations coupled with Bardeen-Cooper-Schrieffer arguments suggest t-FeC can be potential two-dimensional superconductors with 6.77 K superconducting transition temperature.