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Carbon-based oxygen reduction reaction (ORR) catalysts have attracted widespread attention due to their low cost, high conductivity, tunable structures, and excellent stability. In this work, wastepaper was used as a carbon source, while urea and dicyandiamide served as nitrogen sources, to successfully prepare two types of nitrogen-doped carbon nanotubes (N-CNTs) through a one-step pyrolysis method. The physicochemical properties and ORR catalytic performance of the materials were systematically investigated using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. Structural characterization revealed that the urea-derived carbon nanotubes (UCNTs-0.15) possessed a unique wrinkled tubular morphology and exhibited a high pyridinic-N content of up to 20%, significantly higher than the 11% observed in the dicyandiamide-derived sample (DCNTs-0.15). Electrochemical tests demonstrated that UCNTs-0.15 displayed excellent ORR activity in 0.1 mol/L KOH, with an onset potential of 0.94 V and a half-wave potential of 0.74 V (vs. RHE), an electron-transfer number close to 4, and markedly superior stability compared to DCNTs-0.15. Zinc-air batteries assembled with UCNTs-0.15 achieved a peak power density of 80 mW/cm2 and a specific capacity of 644 mA·h/g (based on Zn), and maintained stable cycling for 60 h. Mechanistic studies indicated that urea releases NH3 at low temperatures during pyrolysis, promoting the formation of Fe3N and pyridinic/graphitic N doping, whereas dicyandiamide releases HCN at higher temperatures, leading instead to Fe3C formation and predominantly pyrrolic-N structures. This work elucidates how the choice of nitrogen source regulates the phase of Fe catalysts and nitrogen-release behavior, thereby determining the structure and performance of carbon nanotubes. The findings provide theoretical and experimental insights for the high-value utilization of wastepaper and the sustainable design of electrocatalysts.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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