Tuning the Activity of Molybdenum Carbide MXenes for CO₂ Electroreduction by Embedding the Single Transition-Metal Atom

Abstract

Mo2C electrocatalysts may reduce CO2 to CH4 with the low overpotentials, but also accelerate the hydrogen evolution reaction (HER). Here a series of the transition-metal-embedded Mo2C (M@Mo2C) MXenes are screened by first-principles calculations, and Cr@Mo2C, Mn@Mo2C, Fe@Mo2C, and Co@Mo2C are predicted to have higher activity and selectivity toward CO2ER than HER, compared to the pristine Mo2C. In particular, Fe@Mo2C and Co@Mo2C are quite promising for CO2ER to CH4 or CH3OH at low limiting potentials. In addition, the scaling relationship between the limiting potential and the binding strength of *OH as well as the correlationship among the binding energies of the key intermediates have been investigated, and the binding energy of *OH can serve as the activity descriptor for CO2ER to CH4. Furthermore, Fe@Mo2C may reduce CO2 to C2H4 and CH3CH2OH, which can serve as a potential 2D electrocatalytic material for CO2ER to C1 and C2 products.

MXene-Based Photocatalysts and Electrocatalysts for CO2 Conversion to Chemicals

“…These TM-substituted MXenes also exhibited high stability and excellent CH 4 product selectivity over CO, HCOOH, and CH 3 OH. Meanwhile, the single-atom dopants (Cr, Mn, Fe, and Co) on M-terminal Mo 2 C caused the electron density to be concentrated at the dopant, although this phenomenon was not observed in Ni-, Ru-, or Rh-doped Mo 2 C because of the similar configuration with the pristine Mo 2 C [90]. M-doped Mo 2 C MXenes (M = Cr, Mn, Fe, and Co) have a high ECR activity and selectivity that promote CH 4 and CH 3 OH generation, although CH 4 is energetically unfavorable.…”

“…0.35 eV) compared to the pristine Mo 2 C (0.9 V). Moreover, a smaller *OH binding energy of Fe-doped Mo 2 C could break the inherent linear scaling relationship to trigger high activity for ECR to the C 2 products of C 2 H 4 and CH 3 CH 2 OH [90].…”

“…The theoretical results suggest that the characteristics of bare and -O or -OH terminated MXenes seemed to make ECR preferable to the HER even in acidic conditions because proton adsorption on the MXene surfaces is thermodynamically unfavorable because of the CO 2 -philic surfaces [28,34,35,88,92]. Likewise, the defective MXenes, such as single-metal dopants and metal substitution in the inner layer of M 3 C 2 MXenes, strengthen their CO 2 capture abilities and enhance ECR selectivity against the HER according to energy profiles of all possible H* intermediate configurations [89,90]. Despite the vacancies (V X and V M ) offering promising enhancement in ECR, their strong effect on the fragment-type intermediate adsorption caused some of them to have higher selectivity to the HER than ECR [88].…”

Engineering strategies and active site identification of MXene-based catalysts for electrochemical conversion reactions

“…285 Besides, Fe@Mo 2 C was a promising candidate to form C 2 products, such as C 2 H 4 and CH 3 CH 2 OH, due to the smaller binding energies of key intermediates (OH*), which originated from the binding energy between Fe and O atoms. 286…”

“…285 Besides, Fe@Mo 2 C was a promising candidate to form C 2 products, such as C 2 H 4 and CH 3 CH 2 OH, due to the smaller binding energies of key intermediates (OH*), which originated from the binding energy between Fe and O atoms. 286 Experimentally, Cu was atomically dispersed on Ti 3 C 2 T x by mixing MXene with a Cu precursor, exhibiting 3.6 times higher current density and 3 times higher FE of HCOOH compared to those of pure Ti 3 C 2 T x . 287 The high CO 2 RR catalytic activity originated from the high electron density induced by Cu atoms and the reaction pathway of *HCOOH.…”