Visualization of the surface reconstruction and dynamic catalytic sites of Ni-Fe catalysts for the oxygen evolution reaction by Raman measurements

In situ spectroscopic characterization has been considered as a key method to study catalytic mechanisms. However, most in situ spectroscopic characterizations can only be used to obtain the overall structure of the catalyst, and its spectral intensity depends on the average information about the catalyst as a whole or in a single area, which makes it difficult to determine the real active site of the catalyst. Herein, to overcome the limitations of traditional in situ spectroscopic characterizations, we developed in situ Raman mapping technology to achieve accurate characterizations of active sites during the oxygen evolution reaction (OER), and this work can directly identify and visualize the real active sites of Ni-Fe catalysts for the OER. The in situ Raman mapping technology clearly shows the surface reconstruction process and dynamic active site of the Ni-Fe catalyst during the OER, namely, Ni is converted to NiOOH and the formed NiOOH/Fe-NiOOH as an active site catalyzes the OER. The visualization of the dynamic active site developed in this paper will promote the understanding of the OER catalytic process and can be used in other homo/heterogeneous catalysis fields. In situ spectroscopic characterization has been considered as a key method to study catalytic mechanisms.