Constructing Ru@C 3 N 4 /Cu Tandem Electrocatalyst with Dual-Active Sites for Enhanced Nitrate Electroreduction to Ammonia.

Electroreduction of nitrate to ammonia reaction (NO 3 - RR) is considered as a promising carbon-free energy technique, which can eliminate nitrate from waste-water also produce value-added ammonia. However, it remains a challenge for achieving satisfied ammonia selectivity and Faraday efficiency (FE) due to the complex multiple-electron reduction process. Herein, a novel Tandem electrocatalyst that Ru dispersed on the porous graphitized C 3 N 4 (g-C 3 N 4 ) encapsulated with self-supported Cu nanowires (denoted as Ru@C 3 N 4 /Cu) for NO 3 - RR is presented. As expected, a high ammonia yield of 0.249 mmol h -1  cm -2 at -0.9 V and high FE NH3 of 91.3% at -0.8 V versus RHE can be obtained, while achieving excellent nitrate conversion (96.1%) and ammonia selectivity (91.4%) in neutral solution. In addition, density functional theory (DFT) calculations further demonstrate that the superior NO 3 - RR performance is mainly resulted from the synergistic effect between the Ru and Cu dual-active sites, which can significantly enhance the adsorption of NO 3 - and facilitate hydrogenation, as well as suppress the hydrogen evolution reaction, thus lead to highly improved NO 3 - RR performances. This novel design strategy would pave a feasible avenue for the development of advanced NO 3 - RR electrocatalysts.