Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies
Talshyn Begildayeva, Jayaraman Theerthagiri, Seung Jun Lee, Yiseul Yu, Myong Yong Choi
Abstract
Abstract Herein, the authors produce Co‐based (Co 3 (PO 4 ) 2 , Co 3 O 4 , and Co 9 S 8 ) electrocatalysts via pulsed laser ablation in liquid (PLAL) to explore the synergy of anion modulation on phase‐selective active sites in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Co 3 (PO 4 ) 2 displays an ultralow overpotential of 230 mV at 10 mA cm −2 with 48.5 mV dec −1 Tafel slope that outperforms the state‐of‐the‐art Ir/C in OER due to its high intrinsic activity. Meanwhile, Co 9 S 8 exhibits the highest HER performance known to the authors among the synthesized Co‐based catalysts, showing the lowest overpotential of 361 mV at 10 mA cm −2 with 95.8 mV dec −1 Tafel slope in the alkaline medium and producing H 2 gas with ≈500 mmol g −1 h −1 yield rate under −0.45 V versus RHE. The identified surface reactive intermediates over in situ electrochemical–Raman spectroscopy reveal that cobalt(hydr)oxides with higher oxidation states of Co‐cation forming under oxidizing potentials on the electrode–electrolyte surface of Co 3 (PO 4 ) 2 facilitate the OER, while Co(OH) 2 facilitate the HER. Notably, the fabricated two‐electrode electrolyzers using Co 3 (PO 4 ) 2 , Co 3 O 4 , and Co 9 S 8 electrocatalysts deliver the cell potentials ≈2.01, 2.11, and 1.89 V, respectively, at 10 mA cm −2 . This work not only shows PLAL‐synthesized electrocatalysts as promising candidates for water splitting, but also provides an underlying principle for advanced energy‐conversion catalysts and beyond.