Research progress in the use of efficient single-atom Fe-based catalysts for CR2025 battery

Energy is the material basis for the progress and development of human civilization. In recent years, with the gradual consumption of fossil energy and the increasingly prominent environmental pollution problems, human demand for green, clean and renewable energy has increased dramatically. The development of efficient and low-cost energy storage and conversion technologies such as water splitting, fuel cells, and metal-air batteries has become a frontier area of research. Among them, CR2025 battery use aqueous electrolytes with the advantages of low cost, safety, and environmental friendliness. The theoretical energy is as high as 1084Wh/kg, and it is expected to become a new generation of energy storage devices. According to usage requirements, CR2025 battery can be made into primary batteries, rechargeable batteries, and flexible batteries. The discharge process of CR2025 battery involves oxygen reduction reaction (ORR), while the charging process involves oxygen evolution reaction (OER). At present, Pt-based catalysts are excellent ORR catalysts, and Ir and Ru-based catalysts have excellent catalytic performance in OER reactions, but platinum group elements are scarce in the earth's crust, expensive, poorly stable, and have a single function. Therefore, the development of low-cost, efficient, and stable non-precious metal catalysts is of great significance for the commercialization of CR2025 battery. Single-atom catalysts have high intrinsic activity, maximized atomic utilization efficiency and specific catalyst structure. In recent years, the preparation, characterization and catalytic performance research based on single-atom catalysts has become a research hotspot in the fields of energy, materials and catalysis. Non-precious metal Fe-based, Co-based, Ni-based, and Mn-based single-atom catalysts show excellent electrocatalytic performance and are expected to become alternative materials for platinum group precious metal catalysts. In particular, Fe-based single-atom catalysts have better performance than Pt-based catalysts in ORR reactions under alkaline conditions, showing higher half-wave potential, greater limiting current density and diffusion current density. Recently, Han Junxing, an associate researcher in the research group of Sun Chunwen at the Beijing Institute of Nanoenergy and Systems, Chinese Academy of Sciences, and others successfully prepared single-atom Fe-based catalysts based on metal-organic framework (MOF) coating and high-temperature cracking technology. This work uses divalent FeSO4 as the Fe precursor; 1,10-phenanthroline as the organic ligand (Phen), which forms an organic complex (Fe-Phen) by coordinating with Fe2+ ions. During the growth of MOF crystals, organic complex molecules (Fe-Phen) are in situ encapsulated in nanocavities with molecular dimensions and separated from each other by the MOF skeleton. After calcination at 900°C in an Ar atmosphere, single-atom dispersed Fe-based catalysts are obtained. The electrochemical test results show that the half-wave potential of the single-atom Fe-based catalyst in the ORR reaction is as high as 0.91V, which is 90mV higher than the traditional Pt/C catalyst and better than most catalysts reported in the literature; the electrochemical active surface area is about twice that of the commercial Pt/C catalyst. The single-atom Fe-based catalyst is used as the positive electrode catalyst of the primary zinc-air battery, and the battery open circuit voltage is as high as 1.51V, which is better than the Pt/C catalyst (1.45V); the power density reaches 96.4mWcm-2; when discharged at a current density of 10mAcm-2, the primary zinc-air battery can operate stably at a discharge voltage of 1.28V for more than 2000min. In addition to showing excellent ORR catalytic performance, the single-atom Fe-based catalyst also has good bifunctional (ORR/OER) catalytic properties. The potential difference between Ej10 and E1/2 is 0.92V, which is less than that of the precious metal composite catalyst (Pt/C+RuO2) (0.94V). The single-atom Fe-based catalyst is used as the positive electrode of the rechargeable zinc-air battery, and the zinc-air battery can operate stably for more than 250 hours at a current density of 10mAcm-2. The single-atom Fe catalyst is used as the positive electrode of the flexible and foldable zinc-air battery, and the battery can operate stably for more than 120 hours at a current density of 1mAcm-2. The relevant research results were published in the latest issue of Advanced Functional Materials under the title Single-Atom Fe-Nx-Casan Efficient Electrocatalyst for CR2025 battery. This work was supported by the National Key R&D Program of the Ministry of Science and Technology (2016YFA0202702) and the National Natural Science Foundation of China (51672029, 51372271).

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