Electrochemical Ammonia Oxidation Catalyzed by a Ruthenium Complex with a Dangling Sulfonate Group

The goal of realizing a direct ammonia fuel cell and using ammonia as a hydrogen carrier motivates the development of electrocatalysts for the oxidation of ammonia to nitrogen. Herein, we report [Ru­(bds)­(4-methylpyridine)2] (Ru-bds-Mepy, bds = 2,2′-bipyridine-6,6′-disulfonate) as an efficient electrocatalyst for ammonia oxidation to nitrogen. The decent ammonia oxidation performance of Ru-bds-Mepy was demonstrated by cyclic voltammetry (kobs of 51.47 s–1) and bulk electrolysis (turnover number of 390). The hydrogen bond interaction between the coordination ammonia and the dangling sulfonate group was observed in the crystal structure and further demonstrated by density functional theory (DFT) calculations. Kinetic studies indicate that Ru-bds-Mepy exhibits first-order kinetics with respect to both catalyst and ammonia concentration. Then, DFT calculations suggest the potential of N–N bond formation via the nucleophilic attack of NH3 on the RuVI nitride complex in a barrierless and rapid way. This study contributes an efficient ammonia oxidation catalyst with a record-high turnover number.