ScholarWorks@성균관대학교

초록

Hybrid water electrolysis coupled with the urea electro-oxidation reaction (UOR) enables energy-efficient hydrogen generation while simultaneously treating urea-containing wastewater. Herein, we explore alkaline-earth metal nickelates - barium and strontium nickelates, for their ability to stabilize high oxidation states of Ni, which upon electrochemical activation readily form NiOOH, the active species for UOR. Interestingly, these nickelates distinctly evolve into γ- and β-NiOOH, dictated by the intrinsic chemical properties of the ‘parent’ nickelates. The dynamic formation and transformation of these species during operation are tracked using in situ Raman and X-ray absorption spectroscopy. Electrochemical impedance spectroscopy, long-term stability tests, and post-mortem analyses reveal pronounced differences in COx poison tolerance, active-site evolution, and overall stability. Calculations from the density functional theory attribute the observed trends to variations in hydroxylation tendency, carbonate-ion intercalation, and d-p orbital hybridization, thereby establishing a direct link between the structural attributes of the parent nickelates and the behaviour of the in situ - formed active species. This study thus establishes a direct structure-activity correlation linking the intrinsic chemistry of nickelates to phase-selective NiOOH formation and the resulting variations in electrocatalytic UOR performance.

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