Boron and nitrogen co-doped carbon dots for boosting electrocatalytic oxygen reduction
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摘要: 碳点(CDs)因其较大的比表面积和较快的电子转移特性,已成为能量转换应用领域一种新兴的纳米炭材料。本文以低成本的石油焦为原料,通过简便的一步电化学刻蚀方法制备了硼氮双掺杂碳点(BN-CDs)。与单掺杂碳点B-CDs和N-CDs相比,双掺杂BN-CDs表现出更优异的四电子氧还原电催化活性,具有更正的起始电位(Eonset=0.958 V)和大的扩散极限电流密度(jD=−4.32 mA cm−2),且长期稳定性和甲醇耐受性优于商用Pt/C催化剂。密度泛函理论计算(DFT)研究表明,B、N双掺杂的协同效应促进了O2分子的吸附,有助于提高碳点的电催化活性。本研究为纳米炭材料的设计及其在能量转换领域的应用提供了新的思路。Abstract: Carbon dots (CDs) have become an emerging carbon nanomaterial for use in energy-conversion systems because of their large surface area and rapid electron transfer. Carbon dots (BN-CDs) doped with both boron and nitrogen were synthesized by a simple one-step electrochemical etching approach using low-cost petroleum coke as precursor. Compared with CDs doped with only B or N, BN-CDs showed an excellent four-electron oxygen reduction reaction (ORR) activity with a positive onset potential of 0.958 V and a large diffusion-limited current density of −4.32 mA cm−2. Furthermore, the long-term stability and methanol tolerance of BN-CDs were better than those of a commercial Pt/C catalyst. It was found by density functional theory (DFT) calculation that the co-doping of N and B promoted the adsorption of O2 molecules in the ORR process. This work provides new insight into the rational design of carbon nanomaterials and their use in energy conversion.
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Key words:
- Carbon dots /
- Boron doping /
- Nitrogen doping /
- Oxygen reduction reaction
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Figure 6. (a) CV curves of the BN-CDs, B-CDs and N-CDs in N2 (dotted lines) and O2 saturated (solid lines) environment. (b) RDE LSV curves of BN-CDs, B-CDs, N-CDs and Pt/C at the electrode rotation rate of 1600 r/min. (c) The onset potential and diffusion-limiting current density at 0.3 V of as-prepared samples. (d) RDE LSV curves and the corresponding K-L plots for the BN-CDs. (e) Chronoamperometric responses of BN-CDs and Pt/C catalysts in O2-saturated 0.1 mol L−1 of KOH solution with addition of methanol at 300 s. (f) Chronoamperometric responses of BN-CDs and Pt/C catalysts in O2-saturated 0.1 mol L−1 of KOH solution for 10 h.
Figure 7. Optimized adsorption sites of O2 molecule on (a) BN-CDs (BN-1, BN-2, BN-3, BN-4 and BN-5 structures), (b) B-CDs (BC3 structure) and (c) N-CDs (pyridine N structure) models and their corresponding Eads values. The gray, blue, green, red and white colors represent carbon, nitrogen, boron, oxygen and hydrogen atom, respectively.
Table 1. The elements contents (wt.%) from elemental analysis of petroleum coke precursor.
Elements Contents (wt.%) C 95.66 H 3.40 N 0.46 S 0.16 O* 0.32 *calculated by the subtraction method Table 2. The atomic percent (at.%) from XPS in BN-CDs, B-CDs and N-CDs.
Samples C O N B BN-CDs 58.5 31.9 5.1 4.5 B-CDs 62.4 32.9 - 4.7 N-CDs 67.2 27.2 5.6 - Table 3. The surface N contents (at.%) of BN-CDs and N-CDs.
Samples N-B Pyridinic N Pyrrolic N Graphitic N Oxidized N BN-CDs 10.4 35.4 32.2 14.8 7.2 N-CDs - 31.3 40.7 21.4 6.6 Table 4. The surface B contents (at.%) of BN-CDs and B-CDs.
Samples B-N BC3 BC2O BCO2 BN-CDs 9.2 29.3 42.4 18.1 B-CDs - 27.8 47.5 24.7 -
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