论文总字数：21213字

摘 要

氨是生产化肥的重要的化工原料，是一种重要的无碳能源载体。目前工业制氨主要通过传统的哈伯-博施法来合成，然而该工艺能耗很高且CO₂排放量很大。近年来，以可再生的电能为驱动的，电催化氮还原反应（NRR）制氨的方法引起了国内外学者的广泛关注。然而，该方法的NH₃产率与法拉第效率等目前均不尽如人意。提高上述参数指标的关键在于寻找能够高效地将电能转化为化学能的电化学催化剂。

近年来，碳材料在电催化NRR中表现出取代贵金属Pt的潜能。高效的碳基NRR电催化剂通常需要具备两个重要条件：N掺杂 多孔结构，来保证足够的活性位点和快速的物质传输通道。石墨烯相氮化碳（g-C₃N₄）具有高的N含量、多变的结构及很好的耐温性，这为设计N掺杂的碳材料电催化剂提供了很大的便利。另外，在目前已报道的电化学还原催化剂中，单元子催化剂在有效利用原子与不饱和配位构型方面有着很大优势。本文探讨了四种不同的过渡金属原子以高分散形态负载到g-C₃N₄上（Fe/g-C₃N₄、Co/g-C₃N₄、Mn/g-C₃N₄、Ni/g-C₃N₄）用来作为氮还原反应的催化剂时的电催化性能。研究发现，四种单原子金属中，Fe原子负载于g-C₃N₄作为催化剂时，其催化性能最好。进一步，本文深入分析了当Fe/g-C₃N₄作为氮还原反应催化剂时的催化性能，在-0.71 V vs. RHE下，获得了7.27%的法拉第效率以及6.789 μg h^-1 mg_cat^-1的氨产量。该数据并未达到我们所预计的效果，后续有望通过进一步调控催化剂的形貌来改善提高Fe原子负载于g-C₃N₄性能。

关键词：单原子催化剂 靛酚蓝法 电催化 氮还原

Study and application of transition metal supported g-C₃N₄ unit catalyst in electrocatalytic nitrogen fixation at room temperature and atmospheric pressure

Abstract

Ammonia is an important chemical raw material for the production of chemical fertilizer and an important carbon free energy carrier. At present, industrial ammonia is mainly synthesized by the traditional Haber-Bosch process. However, the process has high energy consumption and large CO₂ emissions. In recent years, the method of electrocatalytic reduction of nitrogen (NRR) to produce ammonia, which is driven by renewable electric energy, has attracted extensive attention of scholars at home and abroad. However, the NH₃ yield and Faraday efficiency of this method are not satisfactory at present. The key to improve the above parameters is to find the electrochemical catalyst which can effectively convert electrical energy into chemical energy.

In recent years, carbon materials have shown the potential to replace Pt in electrocatalytic NRR. Efficient carbon based NRR electrocatalysts usually need two important conditions: N-doping porous structure, to ensure enough active sites and fast material transport channels. Graphene phase carbon nitride (g-C₃N₄) has high N content, variable structure and good temperature resistance, which provides great convenience for the design of N-doped carbon electrocatalyst. In addition, in the reported electrochemical reduction catalyst, the Single-atom catalysts has a great advantage in the effective use of atom and unsaturated coordination configuration. In this paper, the electrocatalytic properties of four different transition metal atoms loaded on g-C₃N₄ (Fe/g-C₃N₄、Co/g-C₃N₄、Mn/g-C₃N₄、Ni/g-C₃N₄) as catalysts for nitrogen reduction were studied. It is found that among the four monoatomic metals, Fe atom supported on g-C₃N₄ is the best catalyst. Furthermore, the catalytic performance of Fe/g-C₃N₄ as a catalyst for nitrogen reduction was analyzed. At -0.71 V vs. RHE, 7.27% Faradic efficiency and 6.789 μg h^-1 mg_cat^-1 ammonia production were obtained. This data did not achieve the expected results, and it is expected to improve the performance of Fe atom loaded on g-C₃N₄ by further adjusting the morphology of the catalyst.

Key Words: Single-atom catalysts; Indophenol blue method; Electrocatalysis; Nitrogen reduction reaction

目 录

摘 要 I

Abstract II

第一章 前言 1

1.1 引言 1

1.2 氮还原反应 2

1.2.1 电催化氮还原反应的反应机理 2

1.2.2 电催化氮还原反应的研究方法 4

1.2.3 与析氢反应的竞争 7

1.3 用于氮还原反应的单原子催化剂 7

1.3.1 贵金属基单原子催化剂 8

1.3.2 非贵金属基单原子催化剂 9

1.4 石墨相氮化碳 9

1.4.1 C₃N₄的发展历史 9

1.4.2石墨相氮化碳（g-C₃N₄）的结构 10

1.4.3 g-C₃N₄的制备方法 11

1.4.4 以g-C₃N₄为载体的单元子催化剂 11

1.5 本论文的研究内容和意义 12

第二章 实验部分 13

2.1 实验试剂 13

2.2 实验仪器 14

2.3 材料的制备 14

2.3.1碳纳米管的活化处理 14

2.3.2 Mn-C₃N₄/CNT、Fe-C₃N₄/CNT、Co-C₃N₄/CNT、Ni-C₃N₄/CNT的合成 14

2.3.3 工作电极的制备 15

2.4 材料的表征 15

2.5 电化学性能测试 15

2.6 紫外分光光度测试 16

2.6.1 NH₃的测定 16

第三章 结果与讨论 19

3.1 四种材料的性能测试 19

3.1 Fe/g-C₃N₄的表征 20

3.2 Fe/g-C₃N₄电催化氮还原反应的研究 21

第四章 结论与展望 24

4.1 结论 24

4.2 展望 24

参考文献 25

致谢 28

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