B₄C₃ Monolayer with Impressive Electronic, Optical, and Mechanical Properties: A Potential Metal-Free Photocatalyst for CO₂ Reduction under Visible Light

Abstract

Visible-light-driven CO2 reduction technology offers a promising solution for the worldwide challenges of climate crisis and energy shortage. A key issue in photocatalysis is to develop environmentally benign, low-cost materials ideally with earth-abundant elements with suitable oxidizing and reducing potentials. Herein, by means of density functional theory computations and swarm-intelligence structure-searching method, we predicted the metal-free two-dimensional B4C3 monolayer as a promising green photocatalyst. Extended from a quasi-planar B4C3 cluster, the newly proposed boron carbide monolayer has not only novel tetracoordinate carbon atoms but also strong visible-light absorption, appropriate band edge alignments, and high carrier mobility, which endow the B4C3 monolayer’s great potential for the photocatalytic CO2 reduction. The computations of Gibbs free energy also suggest the energetic favorability in photoreduction of CO2. Remarkably, as the global minimum structure, the predicted B4C3 sheet is highly realizable in the experiment, as indicated by the impressive in-plane stiffness and weak interaction between the B4C3 and Si substrate.

Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table

“…59,60 The possibly metallic network is formed by strong bonds and is dynamically and thermally stable up to about 2000 K. 59 Another proposed boron carbide is the B 4 C 3 monolayer derived from quasi-planar hexacoordinated B 4 C 3 clusters 61 with tetracoordinate carbon (quasi-ptC). 62 This global minimum structure was obtained by DFT computations and swarm-intelligence structure-searching methods. Since the central B atom of each B 4 C 3 motif is situated about 0.03 nm above the hexagonal B 3 C 3 ring, the monolayer is slightly buckled.…”

“…64 This semiconducting monolayer is thermodynamically and dynamically stable, and maintains its structural integrity up to 1500 K. The plot in Fig. 10(a) displays the cohesive binding energies versus the range of bond lengths found in the nonuniform monolayer structures of BeC, 50 Be 2 C, 51,52 Ca 2 C, 56 CaSi, 57 B 2 C, 58-60 B 4 C 3 , 61,62 and Al 2 C. 63,64 According to the valence-shell electron-pair repulsion (VSEPR) rule, hypercoordinated moieties seem to be energetically unfavorable owing to repulsion of the high density of bonds in the plane. The plot, however, demonstrates surprisingly strong bonding of quasi-planar hypercoordinate structures with their unconventional bonding types.…”

Photocatalytic CO2Reduction: A Review of Ab Initio Mechanism, Kinetics, and Multiscale Modeling Simulations

“…A prime example of such a photocatalyst has been the discovery of g-C 3 N 4 , which has been in recent years investigated as a strong competitor to the traditional TiO 2 . Other purely theoretical studies have hinted at other novel materials, such as B 4 C 3 …”

“…The reduction of CO 2 on the B 4 C 3 monolayer supported on Si was theoretically studied by Chang et al. using the GGA-PBE approach (or HSE06 for band gap calculations) . The authors first checked that the monolayer is thermodynamically and kinetically stable, calculating the phonon dispersion and cohesive energy, and performing ab initio molecular dynamics.…”

“…Chang et al 127 performed calculations on a theoretically feasible material, which was proposed from first-principles based on the success of g-C 3 N 4 , namely a new metal-free catalyst B 4 C 3 . After calculating that the material is experimentally feasible, they performed further electronic calculations to predict its characteristics.…”