Boosting Electrochemical Reduction of Nitrate to Ammonia by Constructing Nitrate-Favored Active Cu-B Sites on SnS2.

The electrochemical reduction of nitrate to ammonia is an effective method for mitigating nitrate pollution and generating ammonia. To design superior electrocatalysts, it is essential to construct a reaction site with high activity. Herein, a simple two-step method is applied to in situ reduce amorphous copper over boron-doped SnS2 nanosheets(denoted as aCu@B-SnS2-x. DFT calculations reveal the combination of amorphous copper and B-doping strategy can construct Cu-B active twins and introduce sulfur vacancies on the surface of the inert SnS2, the active twins can efficiently adsorb nitrate and forcibly separate oxygen atoms from nitrate under the assistance of the exposed Sn atom, leading to strong nitrate adsorption. Benefiting from this, aCu@B-SnS2-x exhibited an ultrahigh NH3 FE of 94.6% at -0.67 V versus RHE and the highest NH3 yield rate of 0.55 mmol h-1 mg-1 cat (9350 µg h-1 mg-1 cat) at -0.77 V versus RHE under alkaline conditions. Besides, aCu@B-SnS2-x is confirmed to remain active after various stability tests, suggesting the practicality of utilizing aCu@B-SnS2-x in industrial applications. This work highlights the feasibility of enhanced nitrate-to-ammonia conversion efficiency by combining the doping method and amorphous metal.

Introducing oxygen vacancies in a bi-metal oxide nanosphere for promoting electrocatalytic nitrogen reduction.

The sluggish breakage of the N-N triple bond, as well as the existence of a competing hydrogen evolution reaction (HER), restricts the nitrogen reduction reaction process. Modification of the catalyst surface to boost N2 adsorption and activation is essential for nitrogen fixation. Herein, we introduced surface oxygen vacancies in bimetal oxide NiMnO3 by pyrolysis at 450 °C (450-NiMnO3) to achieve remarkable NRR activity. The NiMnO3 3D nanosphere with a rough surface could increase catalytically active metal sites and introduce oxygen vacancies that are able to enhance N2 adsorption and further improve the reaction rate. Benefiting from the introduced oxygen vacancies in NiMnO3, 450-NiMnO3 showed excellent performance for nitrogen reduction to ammonia with a high NH3 yield of 31.44 µg h-1 mgcat-1 (at -0.3 V vs. RHE) and a splendid FE of 14.5% (at -0.1 V vs. RHE) in 0.1 M KOH. 450-NiMnO3 also shows high long-term electrochemical stability with excellent selectivity for NH3 formation. 15N isotope labeling experiments further verify that the source of produced ammonia is derived from 450-NiMnO3. The present study opens new avenues for the rational construction of efficient electrocatalysts for the synthesis of ammonia from nitrogen.