Isolated Rhodium Atoms Activate Porous TiO for Enhanced Electrocatalytic Conversion of Nitrate to Ammonia.

The direct electrochemical reduction of nitrate to ammonia is an efficient and environmentally friendly technology, however, developing electrocatalysts with high activity and selectivity remains a great challenge. Single-atom catalysts demonstrate unique properties and exceptional performance across a range of catalytic reactions, especially those that encompass multi-step processes. Herein, a straightforward and cost-effective approach is introduced for synthesizing single-atom dispersed Rh on porous TiO spheres (Rh-TiO), which functions as an efficient electrocatalyst for the electroreduction of NO to NH. The synthesized Rh-TiO catalyst achieve a maximum NH Faradaic efficiency (FE) of 94.7% and an NH yield rate of 29.98 mg h mg at -0.5 V versus RHE in a 0.1 M KOH+0.1 M KNO electrolyte, significantly outperforming not only undoped TiO but also Ru, Pd, and Ir single-atom doped titania catalysts. Density functional theory calculations reveal that the incorporation of Rh single atom significantly enhances charge transfer between adsorbed NO and the active site. The Rh atoms not only serve as the highly active site for electrochemical nitrate reduction reaction (NORR), but also activates the adjacent Ti sites through optimizating the electronic structure, thereby reducing the energy barrier of the rate-limiting step. Consequently, this results in a substantial enhancement in electrochemical NORR performance. Furthermore, this synthetic method has the potential to be extended to other single-atom catalysts and scaled up for commercial applications.