Valence-Shell Electrons and Ionic Radius as Descriptors for Multisite Doping of RuO₂ for Durable Zn-Air Batteries

Multisite doping offers a promising strategy to further improve the bifunctional performance of Ru-based oxides for Zn-air batteries. However, the selection of appropriate additional dopants from the periodic table for RuO₂ still lacks predictive design principles. Based on the dopant properties, we demonstrate that valence-shell electrons and ionic radius can serve as effective descriptors to guide additional dopant selection and elucidate this strategy through lanthanide doping, leveraging the lanthanide contraction effect. It is found that dopants with relatively stable valence-shell configurations (e.g., empty or fully filled subshells) and high valence states are more likely to enhance the oxygen evolution reaction (OER), and dopants with larger ionic radii are more favorable for the oxygen reduction reaction (ORR). Based on the above findings, Ce is identified as the most effective dopant, delivering excellent bifunctional performance with a low potential gap (ΔE) of 0.620 V. Moreover, the high-valence Ta⁵⁺ dopant shows the predicted performance improvement, and the Ce-Ta codoping delivers a high half-wave potential (E_1/2 = 0.884 V) and strong stability. When the CeTa-MnRuO₂ catalyst is used in rechargeable Zn-air batteries, it achieves an open-circuit voltage of 1.57 V, a peak power density of 187 mW cm^-2, and a cycling stability exceeding 1000 cycles at a high current density with negligible voltage decay. This work establishes an effective selection principle for identifying suitable additional dopants using the valence-shell-electrons/ionic-radius descriptor in multisite-doped RuO₂, providing a powerful guideline for designing next-generation, durable Ru-based electrocatalysts.