Lithium-mediated electrochemical nitrogen reduction: Mechanistic insights to enhance performance

Xiyang Cai; Cehuang Fu; Haldrian Iriawan; Fan Yang; Aiming Wu; Liuxuan Luo; Shuiyun Shen; Guanghua Wei; Yang Shao-Horn; Junliang Zhang

doi:10.1016/j.isci.2021.103105

Lithium-mediated electrochemical nitrogen reduction: Mechanistic insights to enhance performance

iScience. 2021 Sep 9;24(10):103105. doi: 10.1016/j.isci.2021.103105. eCollection 2021 Oct 22.

Authors

Xiyang Cai¹, Cehuang Fu¹, Haldrian Iriawan^{2

3}, Fan Yang¹, Aiming Wu¹, Liuxuan Luo¹, Shuiyun Shen¹, Guanghua Wei⁴, Yang Shao-Horn^{2

5}, Junliang Zhang¹

Affiliations

¹ Institute of Fuel Cells, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
² Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
³ Department of Materials, Imperial College London, London SW7 5RB, UK.
⁴ SJTU-Paris Tech Elite Institute of Technology, Shanghai Jiao Tong University, Shanghai 200240, China.
⁵ Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Abstract

Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 μg s^-1 cm^-2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm^-2 geo and 10 mA cm^-2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.

Keywords: Chemical reaction; Chemical synthesis; Electrochemistry.