Theoretical Investigation on the Single Transition-Metal Atom-Decorated Defective MoS₂ for Electrocatalytic Ammonia...

Using density functional theory calculations, we explored the potential of defective MoS₂ sheets decorated with a series of single transition-metal (TM) atoms as electrocatalysts for the N₂ reduction reaction (NRR). The computed reaction free-energy profiles reveal that the introduction of embedded single TM atoms significantly reduces the difficulty to break the N≡N triple bond and thus facilitates the activation of inert nitrogen. Onset potential close to -0.6 V could be achieved by anchoring various TMs, such as Sc, Ti, Cu, Hf, Pt, and Zr, and the formation of the second ammonia molecule limits the overall process. The Ti-decorated nanosheet possesses the lowest free-energy change of -0.63 eV for the potential determining step. To better predict the catalysis performance, we introduced a descriptor, φ, which is the product of the number of valence electron and electronegativity of the decorated TM. It shows a good linear relationship between the d-band center and binding energy of nitrogen, except for those metals with less than half-filled d-band. Although the metals in Group IIIB and IVB have strong adsorption interactions with N atoms, the Gibbs free-energy changes for desorption of the second ammonia are unexpectedly low. The selectivity of these systems toward nitrogen reduction reaction (NRR) is also significantly improved. Therefore, those defective MoS₂ decorated with Sc, Ti, Zr, and Hf are suggested as promising electrocatalysts for NRR, for their both high efficiency and selectivity.