Graphene-Based Phthalocyanine-Assembled Synergistic Fe-Co-Ni Trimetallic Single-Atomic Bifunctional Electrocatalysts by Rational Design for Boosting Oxygen Reduction/Evolution Reactions

Development of high-efficiency bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is vital for the widespread application of zinc–air batteries (ZABs). However, it still remains a great challenge to avoid the inhomogeneous distribution and aggregation of metal single-atomic active centers in the construction of bifunctional electrocatalysts with atomically dispersed multimetallic sites because of the common calcination method. Herein, we report a novel catalyst with phthalocyanine-assembled Fe-Co-Ni single-atomic triple sites dispersed on sulfur-doped graphene using a simple ultrasonic procedure without calcination, and X-ray absorption fine structure (XAFS), aberration-corrected scanning transmission electron microscopy (AC-STEM), and other detailed characterizations are performed to demonstrate the successful synthesis. The novel catalyst shows extraordinary bifunctional ORR/OER activities with a fairly low potential difference (ΔE = 0.621 V) between the OER overpotential (E_j10 = 315 mV at 10 mA cm⁻²) and the ORR half-wave potential (E_half-wave = 0.924 V). Moreover, the above catalyst shows excellent ZAB performance, with an outstanding specific capacity (786 mAh g⁻¹), noteworthy maximum power density (139 mW cm⁻²), and extraordinary rechargeability (discharged and charged at 5 mA cm⁻² for more than 1000 h). Theoretical calculations reveal the vital importance of the preferable synergetic coupling effect between adjacent active sites in the Fe-Co-Ni trimetallic single-atomic sites during the ORR/OER processes. This study provides a new avenue for the investigation of bifunctional electrocatalysts with atomically dispersed trimetallic sites, which is intended for enhancing the ORR/OER performance in ZABs.