Atomically dispersed catalysts (ADCs) or single-atom catalysts have shown high metal atom utilization efficiency and unique catalytic properties that are distinct from bulk or nanoparticle catalysts [1,2]. In ADCs, the coordination structures around central metal atoms significantly affect their catalytic activity and selectivity [3]. However, the control of coordination environments has been achieved mostly in an empirical manner. Especially, the high-temperature annealing step, which is commonly involved during the preparation of ADCs, renders a rational control of coordination environment elusive. We have been working on the development of generalized routes for preparing ADCs [4–6]. In this work, we have developed a low-temperature ligand exchange method that allows for reversibly controlling the coordination structure of the metal center in the ADCs. Modulating the ligand has adjusted the oxidation state of the metal center and consequently changed its catalytic activity and selectivity for oxygen reduction reaction (ORR) in a reversible manner [7]. The CO-ligated atomically dispersed Rh catalyst exhibited ca. 30-fold higher ORR activity than the NH_x-ligated catalyst, whereas the latter showed three times higher H₂O₂ selectivity than the former. Post-treatments of the catalysts with CO or NH₃ gas allowed the reversible exchange of CO and NH_x ligands, which reversibly tuned the oxidation state of metal centers and their ORR activity and selectivity. The reversible ligand exchange reactions were generalized to Ir- and Pt-based catalysts in the same manner.

References

[1] X.-F. Yang, A. Wang, B. Qiao, J. Li, J. Liu, T. Zhang, Acc. Chem. Res. 2013, 46, 1740–1748.

[2] S. K. Kaiser, Z. Chen, D. F. Akl, S. Mitchell, J. Pérez-Ramírez, Chem. Rev. 2020, 120, 11703−11809.

[3] R. Qin, K. Liu, Q. Wu, N. Zheng, Chem. Rev. 2020, 120, 11810−11899.

[4] Y. J. Sa, D.-J. Seo, J. Woo, J. T. Lim, J. Y. Cheon, S. Y. Yang, J. M. Lee, D. Kang, T. J. Shin, H. S. Shin, H. Y. Jeong, C. S. Kim, M. G. Kim, T.-Y. Kim, S. H. Joo, J. Am. Chem. Soc. 2016, 138, 15046−15056.

[5] T. Lim, G. Y. Jung, J. H. Kim, S. O Park, J. Park, Y.-T. Kim, S. J. Kang, H. Y. Jeong, S. K. Kwak, S. H. Joo, Nature Commun. 2020, 11, 412.

[6] J. H. Kim, D. Shin, J. Lee, D. S. Baek, T. J. Shin, Y.-T. Kim, H. Y. Jeong, J. H. Kwak, H. Kim, S. H. Joo, ACS Nano 2020, 14, 1990−2001.

[7] J. H. Kim, D. Shin, J. Kim, J. S. Lim, V. K. Paidi, T. J. Shin, H. Y. Jeong, K.-S. Lee, H. Kim, S. H. Joo, Angew. Chem. Int. Ed. 2021, 60, 20528–20534.