关键词: 空心碳小球, Fe-N-C, Fe₂O₃, 氧还原反应, 锌-空气电池

Abstract:

Oxygen reduction reaction (ORR) plays a profound role in determining cathode performance in metal-air batteries and fuel cells. Owing to its inherently sluggish kinetics, high-performance ORR catalysts which favors the scissoring of O-O bond and formation of O-H bond are a requisite. In this regard, Pt has been explored as the most efficient ORR electrocatalysts. Nevertheless, due to its expensiveness, the usage of Pt catalysts represents one of the major sources of cost in those energy conversion devices. Thus, the development of alternative ORR electrocatalysts with minimized Pt utilization has been widely pursued over the past few decades. Metal-nitrogen-carbon catalysts are expected to replace traditional commercial Pt-C and become a new generation of ORR electrocatalyst. In this paper, using a commercial chain hollow carbon nanosphere (ECP-600JD) with high specific surface area and high conductivity as carbon source and template, Fe₂O₃@Fe-N-C nanocomposite was prepared by a straightforward one-step pyrolysis method as a high-performance ORR electrocatalysts in alkaline media, and its structural characteristics and catalytic performance have been systematically studied. Such a nanocomposite was characterized with large external surface area (467.8 m²·g^-1), high electronic conductivity, as well as the co-existence of Fe-N_x active sites and Fe₂O₃ nanoparticles. Owing to its compositional and structural merits, the optimal Fe₂O₃@Fe-N-C catalyst showed good ORR activity in 0.1 mol·L^-1 KOH solution, with its half-wave potential being 0.84 V. When used in zinc-air batteries, the open circuit voltages of the battery assembled by Fe₂O₃@Fe-NC-1000 and Pt-C were 1.51 V and 1.42 V, respectively. It also demonstrates better rate performance than Pt-C, which can be attributed to the large specific surface area that can provide excellent mass transfer ability under high current density, and its own excellent electrical conductivity was also extremely important. According to the mass of zinc consumed, the specific capacity of the zinc-air battery was calculated, and the specific capacity of the battery assembled with Fe₂O₃@Fe-NC-1000 could reach 776.8 mAh·g_Zn^-1, while the specific capacity of Pt-C under the same conditions was 691.9 mAh·g_Zn^-1. The polarization curve and power density of the catalyst were also obtained. The peak power density of zinc-air battery with Fe₂O₃@Fe-NC-1000 as the cathode reached 88.3 mW·cm^-2, while the peak power density of the battery with Pt-C as the cathode was 76.8 mW·cm^-2. Our research provides a straightforward and easily scalable approach towards the pursuit of high-performance ORR electrocatalysts.

Key words: hollow carbon nanosphere, Fe-N-C, Fe₂O₃, oxygen reduction reaction, zinc-air battery