Operando analysis reveals potential-driven in situ formation of single-Fe-atom electrocatalysts for green production of ammonia
Yang Fa, Ping Song, Xin Ge, Y. Wang, Takao Gunji, Wei Zhang, Xiao Zhao, Weilin Xu
Abstract
As a sustainable approach for N 2 fixation, electrocatalytic N 2 reduction reaction (N 2 RR) to produce ammonia (NH 3 ) 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 N 2 RR. Based on such new type of N 2 RR 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 SA O 4 (OH) 1a to Fe SA O 4 (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 SA O 4 (OH) 1a′ (OH) 1b to Fe SA O 3 (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 N 2 RR, thus revealing the first potential-induced in situ formation of the real electrocatalytic active sites to boost the conversion of N 2 to NH 3 . 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 N 2 RR 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 N 2 RR. 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.