The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl-KCl Eutectics
The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl-KCl Eutectics
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熔融LiCl-KCl共熔体电化学合成氨的可行性
DOI：
10.1002/ange.201909831
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发表时间：
2019
影响因子：
--
通讯作者：
McPherson I
中科院分区：
文献类型：
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作者：
McPherson I
已知熔融 LiCl 和相关的共晶电解质可以高效地将 N2 直接电化学还原为 N3−。有人提出，这可以与电解池中的 H2 氧化相结合，在环境压力下产生 NH3。在这里，这个提议在 LiCl-KCl-Li3N 电池中进行了测试，结果发现情况并非如此，因为之前 N3− 直接电化学氧化为 NH3 的假设过于简单化了。我们发现，在没有施加电流的情况下，添加到熔融电解质中的Li3N会促进H2（H氧化态0）自发且同时化学歧化为H−（H氧化态−1）和以NH2−/NH2−/NH3（H氧化态+1）形式存在的H+，从而导致NH3的非法拉第释放。进一步观察到 NH2− 和 NH2− 拥有自己的氧化还原化学。然而，这些自发反应使我们能够提出另一种真正的催化循环。通过添加LiH而不是Li3N，N2可以被还原为N3−，同时化学计量量的H−被氧化为H2。然后，H2 可以自发地与 N3− 反应形成 NH3，从而再生 H− 并关闭催化循环。初步测试显示，峰值 NH3 合成率为 2.4×10−8mol cm−2s−1，最大电流效率为 4.2 %。用 15 N 2 进行同位素标记确认所得NH 3 来自催化N 2 还原。
Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2to N3−with high efficiency. It had been proposed that this could be coupled with H2oxidation in an electrolytic cell to produce NH3at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3−to NH3is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2(H oxidation state 0) into H−(H oxidation state −1) and H+in the form of NH2−/NH2−/NH3(H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2−and NH2−possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2can be reduced to N3−while stoichiometric amounts of H−are oxidised to H2. The H2can then react spontaneously with N3−to form NH3, regenerating H−and closing the catalytic cycle. Initial tests show a peak NH3synthesis rate of 2.4×10−8mol cm−2s−1at a maximum current efficiency of 4.2 %. Isotopic labelling with15N2confirms the resulting NH3is from catalytic N2reduction.