Enhancing electrocatalytic nitrogen reduction to ammonia with rare earth (La, Y, Sc) on high-index faceted platinum alloy concave nanocubes

Surface structure effect is the key subject in electrocatalysis, and consists of the structure dependence of interaction between reaction molecules and catalyst surface in specifying the surface atomic arrangement, chemical composition and electronic structure. Herein, we develop a controllable synthesis of Pt-RE (RE = La, Y, Sc) alloy concave nanocubes (PtRENCs) with {410} high-index facets (HIFs) by an electrochemical method in choline chloride-urea based deep eutectic solvent. The PtRENCs are used as efficient catalyst in electrocatalytic nitrogen reduction to ammonia (NH3). Owing to the high density of low-coordinated Pt step sites (HIFs structure) and the unique electronic effect of Pt-RE, the as-prepared PtRENCs exhibit an excellent electrocatalytic performance for nitrogen reduction reaction (NRR) under ambient conditions. The NH3 yield rate and Faradaic efficiency (FE) share the same trend of Pt-La (rNH3: 71.4 µg h−1 µg−1cat, FE: 35.6%) > Pt-Y (rNH3: 65.2 µg h−1 µg−1cat, FE: 26.7%) > Pt-Sc (rNH3: 48.5 µg h−1 µg−1cat, FE: 19%) > Pt (rNH3: 25.8 µg h−1 µg−1cat, FE: 10.7%). Moreover, the PtRENCs demonstrate high selectivity for N2 reduction to NH3 and high stability of retaining 90% of NH3 yield rate and FE values for 12 hr continuous NRR tests. Density functional theory (DFT) calculations indicate that the rate determining step of the NRR process is the formation of N2H2* from N2 with the transfer of two proton-coupled electrons, and the upshift of the d-band center boosts the NRR activity by enhancing the bonding strength of reaction intermediates on high-index faceted Pt-RE (RE = La, Y, Sc) alloying surface. In addition, the introduction of RE (RE = La, Y, Sc) on Pt step surface can effectively suppress the HER process and provide appropriate sites for NRR.