School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai, 264209, PR China.
Nanoscale. 2019 Oct 10;11(39):18132-18141. doi: 10.1039/c9nr05402b.
The electrocatalytic synthesis of ammonia (NH3) at ambient temperature is an attractive and challenging subject in the chemical industry. The synthesis of NH3 under ambient conditions requires efficient and stable electrocatalysts with ultralow overpotential to ensure low energy consumption and high NH3 yield. Herein, electrocatalysts consisting of a single transition metal (TM) atom (TM = Mo, Mn, Fe, Co, Ni, or Cu) anchored on 2D M2NO2 MXene (M = Ti, V, and Cr), designated as TM/M2NO2, are designed for N2 reduction reaction (NRR) by density functional theory calculations. The results show that the bonding strength between Mo and Ti2NO2 is strong. The overpotential (ηNRR) of Mo/Ti2NO2 surface-catalyzed NRR is estimated to be as low as 0.16 V via an enzymatic mechanism, which is lower than those reported to date. For Mo/V2NO2 and Mo/Cr2NO2 catalysts, the NRR occurs through the consecutive mechanism and enzymatic mechanism, with corresponding ηNRR values of 0.38 V and 0.22 V, respectively. In addition, the reaction Gibbs free energy of NH3 desorption from the Mo/Ti2NO2 surface is only 0.12 eV. Electronic structure analysis indicates that Mo/Ti2NO2 shows metallic characteristics, which ensures the efficient transfer of electrons between Mo and Ti2NO2. Ab initio molecular dynamics simulations indicate that the Mo atom can be stably immobilized on the Ti2NO2 substrate to prevent its aggregation into Mo clusters. Further analysis illustrates that hydrogen adsorption is not favored on the Mo/Ti2NO2 surface. Mixing the N2 source with extra gases, such as NO2, NO, SO2, SO, and O2, should be avoided for NRR on Mo/Ti2NO2 surface. These predictions offer a new opportunity for the electrocatalytic synthesis of NH3 by N2 reduction in the future.
室温下电催化合成氨（NH3）是化学工业中一个吸引人且具有挑战性的课题。在环境条件下合成 NH3 需要高效且稳定的电催化剂，其超电势要低，以确保低能耗和高 NH3 产率。在此，通过密度泛函理论计算，设计了由单过渡金属（TM）原子（TM = Mo、Mn、Fe、Co、Ni 或 Cu）锚定在二维 M2NO2 MXene（M = Ti、V 和 Cr）上的电催化剂 TM/M2NO2，用于氮气还原反应（NRR）。结果表明，Mo 与 Ti2NO2 之间的结合强度较强。通过酶促机制，Mo/Ti2NO2 表面催化 NRR 的过电势（ηNRR）估计低至 0.16 V，低于迄今为止报道的值。对于 Mo/V2NO2 和 Mo/Cr2NO2 催化剂，NRR 通过连续机制和酶促机制发生，相应的 ηNRR 值分别为 0.38 V 和 0.22 V。此外，NH3 从 Mo/Ti2NO2 表面解吸的反应吉布斯自由能仅为 0.12 eV。电子结构分析表明，Mo/Ti2NO2 表现出金属特性，这确保了 Mo 和 Ti2NO2 之间电子的有效转移。从头算分子动力学模拟表明，Mo 原子可以稳定地固定在 Ti2NO2 基底上，以防止其聚集成 Mo 团簇。进一步的分析表明，Mo/Ti2NO2 表面不利于 H2 吸附。在 Mo/Ti2NO2 表面进行 NRR 时，应避免将 N2 源与额外的气体（如 NO2、NO、SO2、SO 和 O2）混合。这些预测为未来通过 N2 还原电催化合成 NH3 提供了新的机会。
