Operando analysis reveals potential-driven in situ formation of single-Fe-atom electrocatalysts for green production of ammonia

As a sustainable approach for N₂ fixation, electrocatalytic N₂ reduction reaction (N₂RR) to produce ammonia (NH₃) is highly desirable with a precise understanding to the structure-activity relationship of electrocatalysts. Here, firstly, we obtain a novel carbon-supported oxygen-coordinated single-Fe-atom catalyst for highly efficient production of ammonia from electrocatalytic N₂RR. Based on such new type of N₂RR electrocatalyst, by combining operando X-ray absorption spectra (XAS) with density function theory calculation, we reveal significantly that the as-prepared active coordination structure undergoes a potential-driven two-step restructuring, firstly from Fe_SAO₄(OH)_1a to Fe_SAO₄(OH)_1a'(OH)_1b with the adsorption of another -OH on Fe_SA at open-circuit potential (OCP) of 0.58 V_RHE, and subsequently restructuring from Fe_SAO₄(OH)_1a'(OH)_1b to Fe_SAO₃(OH)_1a″ due to the breaking of one Fe-O bond and the dissociation of one -OH at working potentials for final electrocatalytic process of N₂RR, thus revealing the first potential-induced in situ formation of the real electrocatalytic active sites to boost the conversion of N₂ to NH₃. Moreover, the key intermediate of Fe-NNH_x was detected experimentally by both operando XAS and in situ attenuated total reflection-surface-enhanced infrared absorption spectra (ATR-SEIRAS), indicating the alternating mechanism followed by N₂RR on such catalyst. The results indicate the necessity of considering the potential-induced restructuring of the active sites on all kinds of electrocatalysts for such as highly efficient ammonia production from N₂RR. It also paves a new way for a precise understanding to the structure-activity relationship of a catalyst and helps the design of highly efficient catalysts.