10.1021/acsenergylett.9b00382.s001 Yanping Zhu Yanping Zhu Hsiao-Chien Chen Hsiao-Chien Chen Chia-Shuo Hsu Chia-Shuo Hsu Ting-Sheng Lin Ting-Sheng Lin Chia-Jui Chang Chia-Jui Chang Sung-Chun Chang Sung-Chun Chang Li-Duan Tsai Li-Duan Tsai Hao Ming Chen Hao Ming Chen Operando Unraveling of the Structural and Chemical Stability of P‑Substituted CoSe<sub>2</sub> Electrocatalysts toward Hydrogen and Oxygen Evolution Reactions in Alkaline Electrolyte American Chemical Society 2019 bifunctional electrocatalysts P-substituted CoSe 2 electrocatalysts X-ray absorption spectroscopy Raman spectroscopy chemical stability electrolyte liquid-phase transmission electron microscopy CoSe 2 HER operando measurements oxygen evolution reactions Chemical Stability Co cations Operando Unraveling Oxygen Evolution Reactions reactive species P-substituted CoSe 2 electrocatalyst pre-catalyst OER metal chalcogenides cobalt oxyhydroxide Alkaline Electrolyte 2019-03-27 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Operando_Unraveling_of_the_Structural_and_Chemical_Stability_of_P_Substituted_CoSe_sub_2_sub_Electrocatalysts_toward_Hydrogen_and_Oxygen_Evolution_Reactions_in_Alkaline_Electrolyte/7952870 The question of whether the metal chalcogenides (phosphides) that have been acknowledged to be efficient materials for bifunctional electrocatalysts really perform as the active species or just “pre-catalysts” has been debated. Herein, a series of operando measurements, including in situ X-ray absorption spectroscopy, liquid-phase transmission electron microscopy, and in situ Raman spectroscopy, were conducted to unravel in real time the structural and chemical stability of P-substituted CoSe<sub>2</sub> electrocatalysts under both hydrogen and oxygen evolution reactions (HER and OER, respectively) in an alkaline electrolyte. It can be conclusively revealed that, in an alkaline electrolyte, the P-substituted CoSe<sub>2</sub> electrocatalyst was acting as the “pre-catalyst” rather than the real reactive species. The introduction of phosphorus is speculated to generate more vacancies or defects around Co cations in the initial CoSe<sub>2</sub> and considerably facilitates the structural transformation into the “real reactive species”, such as metallic cobalt (for HER) and cobalt oxyhydroxide (for OER).