Well-Defined Iron Sites in Crystalline Carbon Nitride

• Published in: Journal of the American Chemical Society 2023-09, Vol.145 (38), p.20739-20744
• Main Authors: Genoux, Alexandre, Pauly, Magnus, Rooney, Conor L., Choi, Chungseok, Shang, Bo, McGuigan, Scott, Fataftah, Majed S., Kayser, Yves, Suhr, Simon C. B., DeBeer, Serena, Wang, Hailiang, Maggard, Paul A., Holland, Patrick L.
• Format: Article
• Language: English
• Subjects: absorption; ammonia; carbon; carbon nitride; Chemistry; geometry; methanol; nitrate reduction; oxidation; stoichiometry; triazines; X-radiation; X-ray diffraction
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.3c05417

Carbon nitride materials can be hosts for transition metal sites, but Mössbauer studies on iron complexes in carbon nitrides have always shown a mixture of environments and oxidation states. Here we describe the synthesis and characterization of a crystalline carbon nitride with stoichiometric iron sites that all have the same environment. The material (formula C6N9H2Fe0.4Li1.2Cl, abbreviated PTI/FeCl2) is derived from reacting poly­(triazine imide)·LiCl (PTI/LiCl) with a low-melting FeCl2/KCl flux, followed by anaerobic rinsing with methanol. X-ray diffraction, X-ray absorption and Mössbauer spectroscopies, and SQUID magnetometry indicate that there are tetrahedral high-spin iron­(II) sites throughout the material, all having the same geometry. The material is active for electrocatalytic nitrate reduction to ammonia, with a production rate of ca. 0.1 mmol cm–2 h–1 and Faradaic efficiency of ca. 80% at −0.80 V vs RHE.