N-doped carbon encapsulated transition metal catalysts to optimize performance of zinc-air batteries

July 17, 2020

In a report published in NANO, a team of researchers from Sichuan University of Science and Engineering, China have developed N-doped carbon encapsulated transition metal catalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) to optimize performance of zinc-air batteries.

Three-dimensional porous graphene-like carbon layer encapsulated Fe/Fe3C (Fe@NCG) was prepared by pyrolysis of the mixture of Fe- chitosan chelate assembled without solvent and urea with small molecular nitrogen source. The space limiting effect of the chelate suppressed the agglomeration of Fe3+ ions, and the small molecular nitrogen source promoted the regulation of N configuration. The zinc-air battery assembled with Fe@NCG catalyst shows good performance.

The catalyst Fe@NCG shows remarkable ORR/OER bifunctional catalytic activity with a half wave potential of 0.86 V for ORR and a moderate potential difference of 0.85 V in alkaline medium. "The zinc-air battery assembled with Fe@NCG as positive and negative catalyst showed good discharge platform, high peak power density, high energy density, and high cycle stability." says Lei Ying, PhD, the corresponding author of the paper.

What is special about the study is that the Fe@NCG was prepared by pyrolyzing solvent-free formed fechitosan chelates and additional small molecule nitrogen source urea. The in-situ nitrogen doping and etching of self-nitrogen-doped carbonized chitosan by CN gas produced by g-C3N4 decomposition (such as C2N2+, C3N2+, C3N3+) is helpful to the regulation of electronic structure and the formation of pore structure in the carbon skeleton.

Moreover, the uniform distribution of Fe could be attributed to the molecular-level chelating space confinement effect of Fe-chitosan chelate compound precursor, wherein chitosan molecular served as a "fence" to effectively reduce excess aggregation of Fe3+ ions. The group then tested the product electrocatalytic performance.

The work of this team of researchers from Sichuan University of Science & Engineering has led to the exciting development of electrocatalytic materials. This work suggests that a simple and universal strategy can also be extended to the synthesis of other transition metal electrocatalysts coated with carbon.

One of the most fascinating frontiers in this research field might be combining chelating space confinement strategy and regulation of N configuration. Understanding these processes will improve the performance of materials and equipment, which will improve the lives of all of us. More recently, the group has been working on multifunctional conversions of electrocatalytic materials and assembly of devices.
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Additional co-authors of this work are Renxing Huang, Dandan Zhang, Huaming Xie, Xingyong Liu and Honghui Wang. Corresponding author is Ying Lei (lynnely1209@suse.edu.cn).

The research was supported by the National Natural Science Foundation of China (No.61601313 and 21606024), the Opening Project of Sichuan Key Laboratory of Comprehensive Utilization of Vanadium and Titanium Resources (2018FTSZ16), Science and technology plan project of Sichuan Province Science and Technology (No.2017GZ0391), the Key science and technology plan project of Zigong City (No. 2019GYCX12), and the Innovation Fund of Postgraduate of Sichuan University of Science & Engineering (No. y2018055 and y2018056).

For more insight into the research described, readers are invited to access the paper on NANO.

IMAGE

Caption: Fe@NCG was be prepared by pyrolyzing solvent-free formed Fechitosan chelates and additional small molecule nitrogen source urea. The formed catalyst exhibits bifunctional catalytic performance toward ORR and OER in alkaline medium and higher power density and superior charge-discharge durability in zinc-air battery.

NANO is an international peer-reviewed monthly journal for nanoscience and nanotechnology that presents forefront fundamental research and new emerging topics. It features timely scientific reports of new results and technical breakthroughs and publishes interesting review articles about recent hot issues.

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