Highly efficient N2 fixation catalysts: Transition-metal carbides M2C (MXenes)

Shuo Wang, Bo Li, Lei Li, Ziqi Tian, Qiuju Zhang, Liang Chen, Xiao Cheng Zeng

Research output: Contribution to journalArticle

Abstract

The development of highly efficient metal or metal compound electrocatalysts under mild conditions has always been a challenging task for N2 reduction. Herein, we show that pristine two-dimensional (2D) MXenes are promising N2 electroreduction catalysts due in part to the availability of multiple active sites per unit area. We systematically explore a series of 3d, 4d and 5d-transition metal M2C (M = Sc, Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta and Hf) MXenes and compute their limiting potentials for the N2 reduction reaction (NRR). We find that 4d4-Mo2C gives rise to the lowest free-energy barrier (ΔG) of 0.46 eV, among the synthesized M2C MXenes as of today. More importantly, we find that two hypothetical MXenes, 3d5-Mn2C and 3d6-Fe2C, possess even lower ΔG of 0.28 and 0.23 eV, respectively, compared to the state-of-the-art 4d4-Mo2C, thereby likely being more efficient NRR catalysts. The N2 capture strength, a key parameter of the potential-limiting step, is found to be closely related to the d-electron arrangement on the occupied and empty spin-split d-orbitals. Hence, the excellent NRR performance of Mn2C and Fe2C can be attributed to the desirable half-filled 3d5 or 3d6 electron arrangements. The adsorption of N2 on Mn2C results in the donation of 1σ electrons to the empty spin-down 3d orbitals of Mn. The donated electrons weaken the N2 adsorption strength and lower the energy barrier of the potential-limiting step of hydrogenation. The insights obtained from this comprehensive study offer guidance to design new and efficient electrocatalysts for N2 fixation.

Original languageEnglish (US)
Pages (from-to)538-547
Number of pages10
JournalNanoscale
Volume12
Issue number2
DOIs
StatePublished - Jan 14 2020

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Transition metals
Carbides
Catalysts
Electrons
Electrocatalysts
Energy barriers
Metals
Adsorption
Free energy
Hydrogenation
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ASJC Scopus subject areas

  • Materials Science(all)

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Highly efficient N2 fixation catalysts : Transition-metal carbides M2C (MXenes). / Wang, Shuo; Li, Bo; Li, Lei; Tian, Ziqi; Zhang, Qiuju; Chen, Liang; Zeng, Xiao Cheng.

In: Nanoscale, Vol. 12, No. 2, 14.01.2020, p. 538-547.

Research output: Contribution to journalArticle

Wang, S, Li, B, Li, L, Tian, Z, Zhang, Q, Chen, L & Zeng, XC 2020, 'Highly efficient N2 fixation catalysts: Transition-metal carbides M2C (MXenes)', Nanoscale, vol. 12, no. 2, pp. 538-547. https://doi.org/10.1039/c9nr09157b
Wang S, Li B, Li L, Tian Z, Zhang Q, Chen L et al. Highly efficient N2 fixation catalysts: Transition-metal carbides M2C (MXenes). Nanoscale. 2020 Jan 14;12(2):538-547. https://doi.org/10.1039/c9nr09157b
Wang, Shuo ; Li, Bo ; Li, Lei ; Tian, Ziqi ; Zhang, Qiuju ; Chen, Liang ; Zeng, Xiao Cheng. / Highly efficient N2 fixation catalysts : Transition-metal carbides M2C (MXenes). In: Nanoscale. 2020 ; Vol. 12, No. 2. pp. 538-547.
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