Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies

Herein, the authors produce Co-based (Co-3(PO4)(2), Co3O4, and Co9S8) 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(PO4)(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, Co9S8 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 approximate to 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(PO4)(2) facilitate the OER, while Co(OH)(2) facilitate the HER. Notably, the fabricated two-electrode electrolyzers using Co-3(PO4)(2), Co3O4, and Co9S8 electrocatalysts deliver the cell potentials approximate to 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.

Automated summary

In this study, Co-based electrocatalysts were produced using pulsed laser ablation in liquid (PLAL) method. The authors explored the influence of anion modulation on the active sites of the electrocatalysts. The results showed that Co-3(PO4)(2) exhibited high activity in the oxygen evolution reaction (OER), while Co9S8 showed the highest performance in the hydrogen evolution reaction (HER). In situ electrochemical-Raman spectroscopy revealed the formation mechanism of different reactive intermediates. The two-electrode electrolyzers fabricated using these electrocatalysts showed promising potential for water splitting with low cell potentials.