The direct electrocatalytic synthesis of ammonia from N₂ and H₂O by using renewable energy sources and ambient pressure/temperature operations is a breakthrough technology, which can reduce by over 90% the greenhouse gas emissions of this chemical and energy storage process. We report here an in-situ electrochemical activation method to prepare Fe₂O₃CNT (iron oxide on carbon nanotubes) electrocatalysts for the direct ammonia synthesis from N₂ and H₂O. The in-situ electrochemical activation leads to a large increase of the ammonia formation rate and Faradaic efficiency which reach the surprising high values of 41.6 µg mg_cat⁻¹ h⁻¹ and 17%, respectively, for an in-situ activation of 3 h, among the highest values reported so far for non-precious metal catalysts that use a continuous-flow polymer-electrolyte-membrane cell and gas-phase operations for the ammonia synthesis hemicell. The electrocatalyst was stable at least 12 h at the working conditions. Tests by switching N₂ to Ar evidence that ammonia was formed from the gas-phase nitrogen. The analysis of the changes of reactivity and of the electrocatalyst characteristics as a function of the time of activation indicates a linear relationship between the ammonia formation rate and a specific XPS (X-ray-photoelectron spectroscopy) oxygen signal related to O²⁻ in iron-oxide species. This results together with characterization data by TEM and XRD suggest that the iron species active in the direct and selective synthesis of ammonia is a maghemite-type iron oxide, and this transformation from the initial hematite is responsible for the in-situ enhancement of 3–4 times of the TOF (turnover frequency) and NH₃ Faradaic efficiency. This transformation is likely related to the stabilization of the maghemite species at CNT defect sites, although for longer times of preactivation a sintering occurs with a loss of performances.

通过使用可再生能源和环境压力/温度操作，由N ₂和H ₂ O直接电催化合成氨是一项突破性技术，可以将这种化学和能量存储过程的温室气体排放量减少90％以上。我们在这里报告了一种原位电化学活化方法，用于制备Fe ₂ O ₃ CNT（碳纳米管上的氧化铁）电催化剂，用于直接从N ₂和H ₂ O合成氨。原位电化学活化导致大量增加氨生成速率和法拉第效率达到其41.6微克毫克的令人惊讶的高值_猫^-1 ħ ^-原位活化3 h分别为¹％和17％，是迄今为止报道的使用连续流聚合物-电解质-膜电池和气相操作氨气的非贵金属催化剂的最高值合成半纤维素。在工作条件下，电催化剂至少稳定12小时。通过将N ₂切换为Ar进行的测试证明，氨是由气相氮形成的。反应性和电催化剂特性随活化时间变化的分析表明，氨形成速率与与O ^2-有关的特定XPS（X射线光电子能谱）氧信号之间呈线性关系在氧化铁中。该结果与TEM和XRD的表征数据一起表明，在氨的直接和选择性合成中有活性的铁物种是磁赤铁矿型氧化铁，从初始赤铁矿的这种转变负责原位增强3– TOF（周转频率）和NH ₃法拉第效率的4倍。这种转变很可能与CNT缺陷部位的磁赤铁矿种类的稳定有关，尽管对于较长时间的预活化，烧结会发生，但性能会下降。