Ultrasonic Plasma Engineering Toward Facile Synthesis of Single-Atom M-N4/N-Doped Carbon (M = Fe, Co) as Superior Oxygen Electrocatalyst in Rechargeable Zinc–Air Batteries
Kai Chen, Seonghee Kim, Minyeong Je, Heechae Choi, Zhicong Shi, Nikola Vladimir, Kwang Ho Kim, Oi Lun Li
Abstract
Abstract As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N 4 /NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N 4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min −1 . The Co-N 4 /NC presented a bifunctional potential drop of Δ E = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (Δ E = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N 4 was the major active site with superior O 2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N 4 /NC exhibited a specific capacity (762.8 mAh g −1 ) and power density (101.62 mW cm −2 ), exceeding those of Pt/C-Ru/C (700.8 mAh g −1 and 89.16 mW cm −2 , respectively) at the same catalyst loading. Moreover, for Co-N 4 /NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries.