Jiabiao Yan^{a, +}, Jing Zhu^{c, +}, Dawei Chen^a, *, Shuai Liu^d, Xu Zhanga, Shoushan Yu^a,

Zhenhua Zeng^b, * Luhua Jiang^a, *, Fanglin Du^a

^a. College of Material Science and Engineering, Qingdao University of Science and Technology, Zhengzhou Road 53, Qingdao, 266042, China.

E-mail: D. Chen (daweichen@qust.edu.cn), L. Jiang (luhuajiang@qust.edu.cn)

^b. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA. E-mail: Z. Zeng (zeng46@purdue.edu)

^c. Department of Chemical Physics, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, Anhui, China.

^d. School of Mechatronics and Energy Engineering, Ningbo Institute of Technology, Zhejiang University, Ningbo, 315100, China.

Abstract:

Ruthenium-based pyrochlore oxides (A2Ru2O7) have emerged recently as state-of-the-art catalysts for acidic water oxidation, however, the stability still needs to be further improved. Exploring the relationship between the A-site cation and the structure of the active site (Ru) is highly desirable toward for designing efficient electrocatalysts. Herein, we rationally manipulate the A-site atom substitution in Y2Ru2O7 (YRO) by Ho3+, which has the identical ionic radius with Y3+, but higher electronegativity due to the 4f electron effect. It demonstrated that the higher electronegativity could cause the Ru−O−Ru bond angle enlarged and the Ru-O bond length reduced, mitigating the RuO6 octahedral distortion in Ho2Ru2O7 (HRO) for enhancing the intrinsic OER activity. Compared with other pyrochlore oxides, HRO displayed an ultralow overpotential of 215 mV @ 10 mA cm–2 with lower Ru content and higher mass activities, showing long-term (> 60h) stability in acid media. Density functional theory (DFT) calculation revealed that the higher electronegativity of Ho could strengthen the Ru-O covalency, thereby optimizing the free energy of oxygen species (∆GOOH* - ∆GO2) for better catalytic activity. In addition, the higher electronegativity could reduce the oxygen vacancies and improve the formation energy of oxygen vacancies for better resistance to the Ru dissolution. This work reveals the inherent relationship of the A-site atom electronegativity, the lattice structure of the active site, and the activity-stability of the catalysts.