Engineering the Coordination Environment of Ir Single Atoms with Surface Titanium Oxide Amorphization for Superior Chlorine Evolution Reaction.

The chlorine evolution reaction (CER) is essential for industrial Cl 2 production but strongly relies on the use of dimensionally stable anode (DSA) with high-amount precious Ru/Ir oxide on a Ti substrate. For the purpose of sustainable development, precious metal decrement and performance improvement are highly desirable for the development of CER anodes. Herein, we demonstrate that surface titanium oxide amorphization is crucial to regulate the coordination environment of stabilized Ir single atoms for efficient and durable chlorine evolution of Ti monolithic anodes. Experimental and theoretical results revealed the formation of four-coordinated Ir 1 O 4 and six-coordinated Ir 1 O 6 sites on amorphous and crystalline titanium oxides, respectively. Interestingly, the Ir 1 O 4 sites exhibited a superior CER performance, with a mass activity about 10 and 500 times those of the Ir 1 O 6 counterpart and DSA, respectively. Moreover, the Ir 1 O 4 anode displayed excellent durability for 200 h, far longer than that of its Ir 1 O 6 counterpart (2 h). Mechanism studies showed that the unsaturated Ir in Ir 1 O 4 was the active center for chlorine evolution, which was changed to the top-coordinated O in Ir 1 O 6 . This change of active sites greatly affected the adsorption energy of Cl species, thus accounting for their different CER activity. More importantly, the amorphous structure and restrained water dissociation of Ir 1 O 4 synergistically prevent oxygen permeation across the Ti substrate, contributing to its long-term CER stability. This study sheds light on the importance of single-atom coordination structures in the reactivity of catalysts and offers a facile strategy to prepare highly active single-atom CER anodes via surface titanium oxide amorphization.