Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Department of Chemistry and Biochemistry, University of North Carolina-Wilmington, Wilmington, North Carolina 28403, USA.
J Chem Phys. 2019 Jan 28;150(4):041708. doi: 10.1063/1.5048036.
Electrochemical ammonia synthesis could provide a sustainable and efficient alternative to the energy intensive Haber-Bosch process. Development of an active and selective N electroreduction catalyst requires mechanism determination to aid in connecting the catalyst composition and structure to performance. Density functional theory (DFT) calculations are used to examine the elementary step energetics of associative N reduction mechanisms on two low index Fe surfaces. Interfacial water molecules in the Heyrovsky-like mechanism help lower some of the elementary activation barriers. Electrode potential dependent barriers show that cathodic potentials below -1.5 V-RHE (reversible hydrogen electrode) are necessary to give a significant rate of N electroreduction. DFT barriers suggest a larger overpotential than expected based on elementary reaction free energies. Linear Brønsted-Evans-Polanyi relationships do not hold across N-H formation steps on these surfaces, further confirming that explicit barriers should be considered in DFT studies of the nitrogen reduction reaction.
电化学氨合成可为能源密集型哈伯-博世工艺提供一种可持续且高效的替代方案。开发活性和选择性的 N 电还原催化剂需要确定机理，以帮助将催化剂组成和结构与性能联系起来。密度泛函理论 (DFT) 计算用于研究两种低指数 Fe 表面上缔合 N 还原机制的基本步骤能学。Heyrovsky 样机制中的界面水分子有助于降低一些基本的活化势垒。电极电势相关的势垒表明，阴极电势低于-1.5 V-RHE（可逆氢电极）对于获得显著的 N 电还原速率是必要的。DFT 势垒表明，与基于基本反应自由能的预期相比，过电势更大。线性 Brønsted-Evans-Polanyi 关系在这些表面上的 N-H 形成步骤中不成立，这进一步证实了在氮还原反应的 DFT 研究中应该考虑显式势垒。
