An Unveiled Electrocatalysis Essence of NiCo Hydroxides through in Situ Raman Spectroscopy for Urea Oxidation

The electrochemical urea oxidation reaction (UOR) is the performance‐limiting half reaction of urea electrolysis for producing renewable hydrogen energy. Nevertheless, the essence of electrode function mechanism of catalysts remains unclear. Therefore, design and optimization of catalysts are restricted. Herein, an in situ Raman spectroscopy method is employed to directly measure the electrode properties of the NiCo double hydroxides (NiCo DHs) under working conditions. Given definitely evidence, the evolution process of in situ Raman spectra shows that the Ni element is converted to NiOOH under UOR potentials, while the Co dopant is converted to CoOOH and further to higher‐valence CoO 2 species. Obviously, the catalytically active phase toward UOR is really a complex NiOOH–CoOOH–CoO 2 phase. Accurately matched spectral wavenumbers and electrochemical measurements of the catalytic electrodes explicitly reveal that the addition of Co assuredly reduces the onset potential for electroactive NiOOH formation. The Raman results also indicate effects of the NiO bond elongation and increased disorder caused by Co doping. Herein, an important understanding and new mechanistic perspectives for the electrode reaction process of UOR with NiCo binary catalysts are provided.