Electrocatalyst with Dynamic Formation of the Dual-Active Site from the Dual Pathway Observed by In Situ Raman Spectroscopy

Understanding the catalysis mechanism of the sluggish oxygen evolution reaction (OER) involved in water splitting is of vital importance for the development of clean hydrogen energy. Earth-abundant transition-metal (oxy)hydroxide with low cost and high performance is one of the most promising OER catalysts. These catalysts often dynamically and heterogeneously transform from inactive pre-catalysts into active phases under operation conditions, and thus, the operando/in situ method is needed for the direct observation. Herein, using in situ Raman spectroscopy and density functional theory simulation, we correlate the OER activity with the dynamic crystal- and electronic-structure reconstruction of nano-sheet cobalt hydroxide. A complicated dual-transformation path is observed as the applied voltage is gradually increased; the pristine single-phase α-Co(OH)2 catalyst transforms into the hydrous Co(OH)2 phase through hydroxide intercalation, then to mixed β/γ-CoOOH phases through dehydration and dehydrogenation, and finally to OER-active γ-CoOOHx and β-CoOOHy. Moreover, the observed spectral and Tafel behaviors at different scan rates manifest the rate-dependent formation of the dual-active-phase, demonstrating the correlation between the OER ability and thermodynamics of structural reconstruction, which is critical in the fabrication of high-activity catalysts.