Nonprecious Triple-Atom Catalysts with Ultrahigh Activity for Electrochemical Reduction of Nitrate to Ammonia: A DFT Screening.

Electrochemical nitrate reduction to ammonia (NORR) is promising to not only tackle environmental issues caused by nitrate but also produce ammonia at room temperatures. However, two critical challenges are the lack of effective electrocatalysts and the understanding of related reaction mechanisms. To overcome these challenges, we employed first-principles calculations to thoroughly study the performance and mechanisms of triple-atom catalysts (TACs) composed of transition metals (including 27 homonuclear TACs and 4 non-noble bimetallic TACs) anchored on N-doped carbon (NC). We found five promising candidates possessing not only thermodynamic and electrochemical stability, but also high activity and selectivity for ammonia production. Among them, non-noble homonuclear Ni@NC TAC show high activity with low theoretical limiting potential of -0.31 . Surprisingly, bimetallic CoNi@NC, CoCu@NC, and FeNi@NC TACs show ultrahigh activity with theoretical limiting potentials of 0.00 , without a potential determining step in the whole reaction pathways, representing the best theoretical activity been reported up to date. These promising candidates are facilitated by circumventing the limit of scaling relationships, a well-known obstacle for single-atom catalysts. This study indicates that designing suitable TACs can be a promising strategy for efficiently electro-catalyzing NORR and breaking the limit of the scaling relationship.