In situ modification of the d-band in the core-shell structure for efficient hydrogen storage via electrocatalytic N 2 fixation.

The electrochemical N 2 reduction reaction (NRR) into NH 3 , especially powered by clean and renewable electricity, is a promising alternative to the capital- and energy-intensive Haber-Bosch process. However, the inert N[triple bond, length as m-dash]N bond and the frantic competition of the hydrogen evolution reaction lead to a poor NH 3 yield rate and faradaic efficiency (FE). Here, we in situ construct a series of two-dimension core/shell V 2 O 3 /VN nanomeshes with a gradient nitride-layer thickness. Among them, V 2 O 3 /VN-2 exhibits the highest FE of 34.9%, an excellent NH 3 yield rate of 59.7 μg h -1 mg cat. -1 , and outstanding cycle stability, exceeding those of most of the NRR electrocatalysts reported to date. First-principles calculations reveal that the d-band center of VN shifts up in a nearly linear manner with the decrease of nitride-layer thickness, and V 2 O 3 /VN-2 with a d-band center closer to the Fermi level can strengthen the d-2π* coupling between the catalyst and N 2 molecule, notably facilitating the N 2 -into-NH 3 conversion.