Facile synthesis of coral-like nitrogen and sulfur co-doped carbon-encapsulated FeS 2 for efficient electroreduction of nitrate to ammonia

Electro-reduction of nitrate (NO3-) to ammonia is a promising method to transform the environmental contaminant NO3- to value-added ammonia. Since diverse end-products might be formed and a convenient material preparation process is preferable, it is of great importance to facilely synthesize a high-performance electro-catalyst towards ammonia generation with high selectivity. Herein, a coral-like nitrogen (N) and sulfur (S) co-doped carbon-encapsulated FeS2 composite material (FeS2@NSC) was successfully fabricated for effective electro-reduction of high-concentration of NO3- to ammonia through a simple one-step pyrolysis method. The FeS2@NSC-400 material exhibited remarkable electrocatalytic NH3 production performance with the NH3 yield of 4428.35 mu g h(-1) cm(-2) and NH3 Faraday efficiency of 84.75 % at -1.4 V vs. Ag/AgCl, which outperforms many of the reported electrocatalysts. The unique small cluster coral-like core-shell structure, N, S co-doping and the interaction between inner FeS2 and the outer carbon layer greatly enhanced the electrical conductivity and stability of the material and the adsorption of NO3- and intermediate products, thereby facilitating the electrocatalytic performance of nitrate-to-ammonia. The FeS2@NSC material induced the electrocatalytic reduction of NO3- mainly through direct electron transfer instead of the indirect atomic H* mediation, and the main reduction product NH3 was speculated to derive from the pathway of NO3-* -> NO2-* -> NO* -> HNO* -> H2NO* -> H2NOH* -> NH3.