Single -atom anchored novel two-dimensional MoSi 2N4 monolayers for efficient electroreduction of CO 2 to formic acid and methane

2025-05-03 0 0 625.72KB 17 页 10玖币

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Single-atom anchored novel two-dimensional

MoSi2N4 monolayers for efficient electroreduction of

CO2 to formic acid and methane

Wei Xuna*, Xiao Yanga, Qing-Song Jianga, Ming-Jun Wangb*, Yin-Zhong Wuc, Ping

Lid*

a Faculty of Electronic Information Engineering, Huaiyin Institute of Technology,

Huaian 223003, China (xunwei@hyit.edu.cn)

a Faculty of Electronic Information Engineering, Huaiyin Institute of Technology,

Huaian 223003, China (yangxiao@hyit.edu.cn)

a Faculty of Electronic Information Engineering, Huaiyin Institute of Technology,

Huaian 223003, China (jiangqingsong05@hyit.edu.cn)

b School of Automation and Information Engineering, Xi’an University of Technology,

Xi’an, Shaanxi 710048, China (wangmingjun@xaut.edu.cn)

c School of Physical Science and Technology, Suzhou University of Science and

Technology, Suzhou 215009, China (yzwu@usts.edu.cn)

d State Key Laboratory for Mechanical Behavior of Materials, Center for Spintronics

and Quantum System, School of Materials Science and Engineering, Xi’an Jiaotong

University, Xi’an, Shaanxi 710049, China (pli@xjtu.edu.cn)

Abstract

Efficient and selective CO2 electroreduction into value-added chemicals and fuels

emerged as a significant approach for CO2 conversion, however, it relies on catalysts

with controllable product selectivity and reaction paths. In this work, by means of first-

principles calculations, we identify five catalysts (TM@MoSi2N4, TM = Sc, Ti, Fe, Co

and Ni) comprising transition-metal atoms anchored on a MoSi2N4 monolayer, whose

catalytic performance can be controlled by adjusting the d-band center and occupation

of supported metal atoms. During CO2 reduction, the single metal atoms function as the

active sites activates the MoSi2N4 inert basal-plane, and as-designed electrocatalysts

exhibit excellent activity in CO2 reduction. Interestingly, HCOOH is the preferred

product of CO2 reduction on the Co@MoSi2N4 catalyst with a rate-determining barrier

of 0.89 eV, while the other four catalysts prefer to reduce CO2 to CH4 with a rate-

determining barrier of 0.81-1.24 eV. Moreover, MoSi2N4 is an extremely-air-stable

material, which will facilitate its application in various environments. Our findings

provide a promising candidate with high activity, catalysts for renewable energy

technologies, and selectivity for experimental work.

Keywords: Electrochemical CO2 reduction; Single atom catalysts; 2D materials;

Density functional theory

1. INTRODUCTION

Because of the continuing increase in the emissions of CO2 from excessive fossil

fuel usage, the reduction of CO2 into environmentally friendly, high-efficiency, and

low-cost alternative fuels such as formic acid (HCOOH), methanol (CH3OH), and

methane (CH4) is recognized as one of the most promising approaches that would

positively impact the global carbon balance and energy storage1-6. Since CO2 is an

extremely stable and nonreactive molecule, converting CO2 into fuels is a scientifically

challenging problem requiring appropriate catalysts and high energy input2. Single

atom catalysts (SACs), first proposed for CO oxidation in 20117, provide efficient

activation and conversion of CO2 using transition metal (TM) atoms8–16. The

coexistence of empty and occupied TM d-orbitals can accept lone-pair electrons, and

then back-donate these electrons to the antibonding orbitals to weaken the C=O bonds.

Remarkably, since two dimensional (2D) materials have large surface-to-volume

ratios, short carrier diffusion distances, unique electronic properties, and abundant

active sites, they serve as promising substrates for atomically dispersed transition metal

atoms for CO2 reduction. To date, most of the discovered monolayer 2D materials have

a thickness of n ≤7. Graphene monolayer is famous six-membered ring (SMR)

materials17 of n = 1, which have been a central topic for CO2 reduction18–28. The silicon

counterpart of graphene (n = 2), has also shown great potential for CO2 reduction29, 30.

For n = 3, monolayer transition-metal dichalcogenides are the most studied SMR

materials. In particular, the reduction of CO2 to methanol can be achieved with the

MoS2 supported single Co atom catalyst31. Among the family of n = 4, monolayer group

III chalcogenides have attracted growing interest. For instance, TM@InSe catalysts

based on 2D InSe and transition metal atoms are candidates for CO, HCOOH, and CH4

production32. The 2D In2Se3, the representative systems of n = 5, Anchoring different

single TM atoms shows the great electrocatalytic ability of CO2 reduction via

ferroelectric switching33. Recently, CaMg was found to have a sextuple layer (n = 6)

structure, but there is no research about CO2 reduction34.

Recently, a new compound of septuple layer SMR material, MoSi2N4, has been

successfully, which has a band-gap of ~1.94 eV with excellent ambient stability35. The

MoSi2N4 monolayer can be built by intercalating a 2H-MoS2-type MoN2 layer (n = 3)

into an α-InSe-type Si2N2 (n = 4). Motivated by the extensive research attention of

MoSi2N4 and the reported interesting electronic and catalytic properties36−46, it is of

great fundamental interest to determine whether the emerging 2D MoSi2N4 materials

can be applied to other important electrocatalytic reactions, such as the CO2 reduction

reaction (CO2RR).

In this work, we theoretically investigate the potential of using transition metal

decorated MoSi2N4 monolayers for electrochemical CO2 reduction into hydrocarbon

fuels. Our efforts identify five catalysts with singly dispersed TM atoms anchored on

the 2D MoSi2N4 monolayer (denoted as TM@MoSi2N4, where TM = Sc, Ti, Fe, Co and

Ni). The differential charge density demonstrated that TM atoms form strong

interactions with MoSi2N4 by exchanging electron density. With the increase in atomic

number, the net electron transfer of TM atoms to CO2 decreases, indicating that CO2

activation changes from strong to weak. Anchoring different TM atoms can not only

alter the reaction barrier and paths of CO2 reduction, but also lead to different final

products. These performance improvements stem from the synergistic effects of the

adjusted empty and occupied d-orbitals (d orbital center) of the adsorbed metal atom,

electron transfer, and CO2 adsorption energies. These SACs and catalytic mechanisms

introduce a feasible approach to significantly improve the efficiency of the CO2RR.

2. COMPUTATIONAL METHODS

DFT calculations were performed by using the Vienna Ab Initio Simulation

Package (VASP)47, 48. The exchange−correlation interactions were treated within the

generalized gradient approximation (GGA)49 in the form of the

Perdew−Burke−Ernzerhof (PBE) functional50. The van der Waals interactions were

described using the Bayesian Error Estimation Exchange-correlation functional (BEEF-

vdw)51. The electron wave functions were expanded using plane waves with a cutoff

energy of 500 eV, and the convergence criteria for the residual force and energy on each

atom during structure relaxation were set to 0.002 eV/Å and 10−6 eV, respectively. The

vacuum space was more than 20 Å, which was enough to avoid interactions between

periodic images. The dipole correction is taken into account for all the asymmetric

structures52. The single-atom catalysts were modelled by depositing one metal atom on

2×2×1 supercell MoSi2N4. The Brillouin zone (BZ) was sampled with a

Monkhorst−Pack mesh with a 6 × 6 × 1 kpoint grid in reciprocal space during geometry

optimization, and a 12×12×1 kpoint grid to calculate the electronic properties of all

systems. The Gibbs free energy is calculated using a hydrogen electrode model (CHE)53,

and the solvent effect is considered with the implicit solvent model implemented in

VASPsol33, 54. The site-specific charge differences were obtained using Bader analysis.

3. RESULTS AND DISCUSSION

Due to the large band gap (1.94 eV) of the MoSi2N4 monolayer, not enough

electrons are injected into the antibonding 2πu orbitals of CO2 so that the strong sp-

hybridization symmetry of the carbon atom cannot be disrupted55. Therefore, the

MoSi2N4 material itself is not suitable as a catalyst for CO2 reduction. Our theoretical

study also confirmed this point: by adsorption on MoSi2N4, the inherent linear O=C=O

structure of CO2 molecules can be well maintained (see Supplementary Fig. S1).

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Single-atomanchorednoveltwo-dimensionalMoSi2N4monolayersforefficientelectroreductionofCO2toformicacidandmethaneWeiXuna*,XiaoYanga,Qing-SongJianga,Ming-JunWangb*,Yin-ZhongWuc,PingLid*aFacultyofElectronicInformationEngineering,HuaiyinInstituteofTechnology,Huaian223003,China(xunwei@hyit.edu.cn)aFaculty...

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Single -atom anchored novel two-dimensional MoSi 2N4 monolayers for efficient electroreduction of CO 2 to formic acid and methane

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