Boosting Electrocatalytic N2 Reduction to NH3 over Two-Dimensional Gallium Selenide by Defect-Size Engineering.
2020
Using density functional
theory calculations, we propose that the exposed Ga atom in a two-dimensional
defective gallium selenide monolayer (V-GaSe) can display a good dinitrogen
fixation capacity and an excellent nitrogen reduction reaction (NRR)
performance. Our results show that N2 can be captured by
three sp3-hybridized Ga atoms due to the pulling effect.
With the enlargement in vacancy size through applying tensile strain,
the adsorption of N2 is strengthened and the electrochemical
NRR performance is enhanced. On 8% strained V-GaSe, the estimated
onset potential is as low as 0.30 V. Inspired by the concept of “defect-size-dependent”
NRR performance, we further design a Janus V-GaInSe2 structure
in which the natural size of the cavity is enlarged and the electron
density of the active Ga atoms is enriched. It is found that N2 adsorption is demonstrably enhanced with respect to V-GaSe.
On 4% strained V-GaInSe2, the onset potential is calculated
to be 0.31 V, which is the same as the 8% strained V-GaSe. Moreover,
the produced NH3 can be removed rapidly with a free-energy
change of less than 0.52 eV, which is much lower than those of most
reported catalysts with low overpotentials. Meanwhile, the side hydrogen
evolution reaction is successively suppressed as the strain increases.
Our work offers a feasible method that utilizes the size of a defect
to tune the NRR performance, adding a new understanding of N2 fixation and sustainable NH3 production.
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