Pyrrole-type TM-N3 sites as high-efficient bifunctional oxygen reactions electrocatalysts: From theoretical prediction to experimental validation

Abstract

Efficient catalysis of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for the rechargeable zinc-air batteries (R-ZABs). However, challenges remain due to the scarcity of effective bifunctional electrocatalysts and limited understanding of the structure-activity relationships. Pyrrole-type single-atom catalysts (SACs) with unique electronic structures have emerged as promising electrocatalysts. In this work, we combine density functional theory (DFT) calculations and experimental studies to systematically explore the structure-activity relationships and potential of pyrrole-type transition metal-N₃ (TM-po-N₃) as bifunctional catalysts. DFT calculations reveal that differences in the dependence of ORR and OER activities on the free energy of adsorption of reaction intermediates significantly affect the TM-po-N₃ bifunctional activity and identify magnetic Cu-po-N₃ as the best candidate. The bifunctional activity of Cu-po-N₃ originates from interactions between spin-polarized out-of-plane Cu_3d and O_2s+2p orbitals. Theoretical predictions are validated experimentally, showing that the synthesized Cu-SAC/NC exhibits excellent bifunctional performance with a small potential gap of 0.666 V. Additionally, the assembled R-ZABs display a high-power density of 170 mW cm⁻² and long-term stability, with the charge-discharge voltage gap increasing by only 0.01 V over 240 h. This work provides new insights into the design of efficient bifunctional catalysts.