Electrocatalytic Ammonia Oxidation by a Ruthenium Complex Bearing a 2,6-Pyridinedicarboxylate Ligand
Jun Li, Xiaohuo Shi, Feiyang Zhang, Xingyu Lu, Ya-Qiong Zhang, Rong‐Zhen Liao, Biaobiao Zhang
Abstract
High Resolution Image Download MS PowerPoint Slide Molecular catalysts for the electrocatalytic ammonia oxidation reaction (eAOR) have much to offer in terms of mechanistic investigations and practical energy issues. This work reports the use of complex [Ru(pdc-κ-N 1 O 2 )(bpy)(NH 3 )] ( Ru-NH 3 ) (H 2 pdc = 2, 6-pyridinedicarboxylic acid; bpy = 2,2′-bipyridine) bearing a readily accessible pdc 2– ligand to catalyze ammonia oxidation under electrochemical conditions. The rich structural variations of Ru-NH 3 in coordinating solvents and an ammonia atmosphere were fully characterized by cyclic voltammograms (CVs), NMR, and XRD. CV experiments showed that Ru-NH 3 promotes electrocatalytic ammonia oxidation at a low overpotential of 0.85 V with a calculated catalytic rate ( k obs ) of 18.9 s –1 . Controlled potential electrolysis (CPE) at an applied potential of 0.3 V vs Fc +/0 achieves 76.1 equiv of N 2 with a faradaic efficiency of 89.8%. Experimental and computational analyses indicated that oxidation of Ru-NH 3 generates a reactive Ru III -NH 3 intermediate, which undergoes sequential electron and proton transfer steps to form a Ru VI ≡N species. N–N bond formation occurs via the nucleophilic attack of an ammonia molecule on the Ru VI ≡N moiety with a facile barrier of 8.6 kcal/mol. Eventually, N 2 evolved as the product after releasing two electrons and three protons.