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Modulating Spin-States of Active Catalysts for Efficient Urea Oxidation in Anion Exchange Membrane Electrolyzer
Anamika Yadav1, Trinh Hai Binh2, Ayusie Goyal1
1Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India.
Abstract:
The electronic properties of active M(O)OH catalysts can be effectively modified by tailoring the characteristics of their corresponding precatalysts. Herein, we report a coordination site-modulated precatalyst to access active catalysts for efficient electrocatalytic urea oxidation in an anion exchange membrane (AEM) electrolyzer. A two-dimensional NiFe-coordination polymer (NiFe-2D) was constructed via selective site engineering using hydrazine. Upon electrochemical reconstruction, NiFe-2D was transformed into an active Fe-Ni(O)OH catalyst (AC-2D). X-ray absorption spectroscopy (XAS) confirmed the changes in the coordination and electronic environment of AC-2D with a tuned spin state. Remarkably, AC-2D delivered a current density of 100 mA cm-2 at 1.50 V vs. RHE for the oxygen evolution reaction (OER) and 1.40 V vs. RHE for the urea oxidation reaction (UOR). AC-2D also delivered outstanding performance in an AEM electrolyzer, achieving a current of 4 A at 2.9 V cell voltage and maintaining operation for over 8 days for UOR-assisted water splitting. In situ electrochemical impedance spectroscopy (EIS) and kinetic analysis suggested facile charge transfer during OER and UOR in AC-2D. In situ Raman studies revealed that Ni4+ species were identified as the main active centers for OER, while Ni3+ species served as the catalytic sites for UOR.
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