Enhancing Electrocatalytic N 2 Conversion to NH 3 by MnO 2 Ultralong Nanowires with Oxygen Vacancies

摘要

Background: At present, industrial synthesis of NH 3 mainly relies on the Haber-Bosch process, which is characterized by harsh reaction conditions and high energy consumption. Electrochemical nitrogen reduction is considered to be a mild and sustainable alternative method for producing NH 3 , but efficient electrocatalyst under ambient conditions is the prerequisite for NH 3 production. Objective: To demonstrate that CP@MnO 2 ultralong nanowires are a highly-efficient electrocatalyst for N 2 reduction reaction (NRR) under ambient conditions. Methods: The α-phase MnO 2 synthesized by one-step hydrothermal method has an ultralong nanowires structure and oxygen vacancy defects. The catalysts were characterized by XRD, TEM, XPS, etc. The produced NH 3 was estimated by indophenol blue method by UV-vis absorption spectra. Results: Such catalyst attains high Faradaic efficiency (FE) of 8.8 and a large NH 3 yield of 1.13×10 −10 mol cm −2 s −1 at −0.7 V versus reversible hydrogen electrode in 0.1 M Na 2 SO 4 . In addition, the catalyst also shows high electrochemical stability and selectivity for NH 3 formation. Conclusion: MnO 2 ultralong nanowires can expose higher density of active sites and the spontaneously formed oxygen vacancies can manipulate the electronic structure of manganese oxides and provide coordination unsaturation sites (CUS) to enhance the adsorption of N 2 , which is the main reason for the high activity of the catalyst.