Non-Noble Metal Incorporated Transition Metal Dichalcogenide Monolayers for Electrochemical CO2 Reduction: A First-Principles Study.

Using non-noble metal atoms as catalysts is attractive for decreasing the cost of the CO2 reduction reaction (CO2RR). By screening first-row transition metals and noble metals through extensive first-principles calculations, non-noble Sc and Ti single atoms binding on vacancy-defected transition metal dichalcogenide (TMD) monolayers exhibit better catalytic performance and selectivity for electrochemical CO2RR than noble metal single atoms. The overpotentials of Sc and Ti atoms for the CO2RR can be reduced lower than 0.09 V after applying suitable biaxial tensile strains on vacancy-defected TMDs, which are approximately 1 order of magnitude lower than that of most reported metal atom catalysts. The vacancy defects of TMDs and charge transfer to metal atoms induced by tensile strain play a key role in improving the catalytic activity of non-noble metal single atoms. These results highlight a possible way to design new single atom catalysts for electrochemical CO2RR by utilizing the combination of non-noble metal atoms, defected TMDs, and strain engineering.

Strain-mediated oxygen evolution reaction on magnetic two-dimensional monolayers.

By screening 56 magnetic 2D monolayers through first-principles calculations, it was found that 8 magnetic 2D monolayers (CoO2, FeO2, FeSe, FeTe, VS2, VSe2, VTe2 and CrSe2) can bind O*, OH* and OOH* intermediates of the oxygen evolution reaction (OER), in which the overpotentials of CoO2, FeO2, VSe2, and VTe2 monolayers are 0.684, 1.107, 0.863 and 0.837 V, respectively. After applying suitable biaxial tensile strains, the overpotentials of CoO2, FeO2 and VTe2 monolayers are reduced over 40%. In particular, the overpotentials of CoO2 and VTe2 monolayers decrease to 0.372 V and 0.491 V under the biaxial tensile strains of 4.0% and 3.0%, respectively, which are comparable to the reported overpotentials of noble metal and low-dimensional materials. Tensile strains modify the potential determining step for the OER and enhance the catalytic activity of metal atoms of magnetic 2D monolayers. Magnetic 2D monolayers could be activated by strain engineering as catalysts for the OER.

Wrinkle facilitated hydrogen evolution reaction of vacancy-defected transition metal dichalcogenide monolayers.

Utilizing transition metal dichalcogenides (TMDs) as catalysts in the hydrogen evolution reaction (HER) is a promising prospect for hydrogen production. Here, by first-principles calculations we reveal that the catalytic activities of vacancy-defected TMD MX2 (M = Mo or W and X = S, Se or Te) monolayers for the HER can be significantly improved by wrinkle engineering. The hydrogen adsorption Gibbs free energies of defected TMDs decrease with decreasing wrinkle length. By appropriately controlling and adjusting the wrinkle size and vacancy number, the hydrogen adsorption Gibbs free energy will be close to zero, allowing the wrinkled TMDs to reach their optimum catalytic capability. The improvement of the catalytic activity of TMDs is mainly attributed to the charge transfer and polarization enhancement of metal atoms at the vacancy sites, which are caused by the coupling effect of vacancy defects and wrinkling deformation induced flexoelectricity. These results provide an attractive route for the application of TMDs in hydrogen production by combining wrinkle engineering and defect engineering.