Elucidating Synergistic Mechanisms of Adsorption and Electrocatalysis of Polysulfides on Double-Transition Metal MXenes for Na-S Batteries

Md Shahriar Nahian; Rahul Jayan; Thanayut Kaewmaraya; Tanveer Hussain; Md Mahbubul Islam

doi:10.1021/acsami.1c22511

Elucidating Synergistic Mechanisms of Adsorption and Electrocatalysis of Polysulfides on Double-Transition Metal MXenes for Na-S Batteries

ACS Appl Mater Interfaces. 2022 Mar 2;14(8):10298-10307. doi: 10.1021/acsami.1c22511. Epub 2022 Feb 15.

Authors

Md Shahriar Nahian¹, Rahul Jayan¹, Thanayut Kaewmaraya^{2

3}, Tanveer Hussain⁴, Md Mahbubul Islam¹

Affiliations

¹ Department of Mechanical Engineering, Wayne State University, Detroit, Michigan 48202, United States.
² Department of Physics, Khon Kaen University, Khon Kaen 40002, Thailand.
³ Institute of Nanomaterials Research and Innovation for Energy (IN-RIE), NANOTEC-KKU RNN on Nanomaterials Research and Innovation for Energy, Khon Kaen University, Khon Kaen 40002, Thailand.
⁴ School of Science and Technology, University of New England, Armidale, New South Wales 2351, Australia.

PMID: 35167253
DOI: 10.1021/acsami.1c22511

Abstract

Multiple unfavorable features, such as poor electronic conductivity of sulfur cathodes, the dissolution and shuttling of sodium polysulfides (Na₂S_n) in electrolytes, and the slower kinetics for the decomposition of solid Na₂S, make sodium-sulfur batteries (NaSBs) impractical. To overcome these obstacles, novel double-transition metal (DTM) MXenes, Mo₂TiC₂T₂, (T = O and S) are studied as an anchoring material (AM) to immobilize higher-order polysulfides and to expedite the otherwise slower kinetics of insoluble short-chain polysulfides. Density functional theory (DFT) calculations are carried out to justify and compare the effectiveness of Mo₂TiC₂S₂ and Mo₂TiC₂O₂ as AMs by analyzing their interactions with S₈/Na₂S_n (n = 1, 2, 4, 6, and 8). Mo₂TiC₂S₂ provides moderate adsorption strength compared to Mo₂TiC₂O₂, therefore, it is expected to effectively inhibit Na₂S_n dissolution and shuttling without causing decomposition of Na₂S_n. The calculated Gibbs free energies of the rate-determining step for sulfur reduction reactions (SRR) are found to be significantly lower (0.791 eV for S and 0.628 eV for O functionalization) than that in vacuum (1.442 eV), suggesting that the SRR is more thermodynamically favorable on Mo₂TiC₂T₂ during discharge. Additionally, both Mo₂TiC₂S₂ and Mo₂TiC₂O₂ demonstrated effective electrocatalytic activity for the decomposition of Na₂S, with a substantial reduction in the energy barrier to 1.59 eV for Mo₂TiC₂S₂ and 1.67 eV for Mo₂TiC₂O₂. While Mo₂TiC₂O₂ had superior binding properties, structural distortion is observed in Na₂S_n, which may adversely affect cyclability. On the other hand, because of its moderate binding energy, enhanced electronic conductivity, and significantly faster oxidative decomposition kinetics of polysulfides, Mo₂TiC₂S₂ can be considered as an effective AM for suppressing the shuttle effect and improving the performance of NaSBs.

Keywords: DFT; double-transition metal MXene; electrocatalysis; shuttle effect; sodium−sulfur batteries.