Boosting Zinc-Air Battery Performance by Regulating Pd Single-Atom Coordination via Thermal-Driven Migration

Pd catalysts showed considerable activity to the oxygen conversions in metal-air batteries, but developing efficient, durable, and low-cost Pd electrocatalysts remains highly challenging. Herein, a Pd single-atom catalyst (SAC) with in-plane PdN_xC_4-x (1 ≤ x ≤ 4) moieties was reconstructed at 800 °C (Pd₁/hNCNC-800) by heating the counterpart with edge-coordinated PdN₂Cl₂ single sites formed on hierarchical N-doped carbon nanocages at 70 °C (Pd₁/hNCNC-70). In alkaline media, the Pd₁/hNCNC-800 catalyzes oxygen reduction (ORR) and oxygen evolution (OER) reactions via dominant four-electron pathways as revealed by electrochemical and in situ Raman spectroscopy characterizations, exhibiting outstanding activities and stabilities. The corresponding zinc-air battery demonstrates a maximum power density of 214.4 mW cm^-2, a high specific capacity of 810.7 mAh g_Zn^-1, and a long cycle life over 600 h, significantly outperforming the counterparts of Pd₁/hNCNC-70 and mixed Pt/C+RuO₂ (commercial). Theoretical calculations reveal that multiple PdN_xC_4-x moieties collectively boost the ORR/OER processes while efficiently inhibiting the migration of Pd atoms. These findings establish the correlation between coordination structure and ORR/OER performance of Pd SACs, providing guidance to develop advanced catalysts for energy applications.