Flower-Like Ni–Mn Bimetallic Oxide-Based Nanosheets for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

Bimetallic oxides generally exhibit excellent electrochemical properties because of their strong electrocatalytic activity and the synergistic effects between different metals. In this work, three-dimensional flower-like nickel–manganese bimetallic oxides @ carbon cloth (NiMnOx@CC) were synthesized by in situ growth on carbon cloth with a simple hydrothermal reaction. The effects of different metal salt ratios on the structure and electrochemical properties of bimetallic oxides were studied systematically. Morphologies and microstructures of all samples were verified by field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Our results showed that when the molar ratio of nickel–manganese reaches 1:1, the bimetal oxidation morphology has a regular flower-like structure, formed by the staggered accumulation of nanosheets. The obtained typical catalyst NiMnOx-3@CC possesses high ammonia yield (16 μg–1 h–1 mg–1) and Faraday efficiency (FE) (19%) at −0.1 V vs. reversible hydrogen electrode (RHE), which is attributed to the synergistic effects between nickel and manganese oxides. On the one hand, this unique cross-stacking structure of nanosheets can effectively avoid the aggregation of catalysts, which is conducive to providing more active sites; on the other hand, the abundance of oxygen vacancy is conducive to the adsorption and activation of nitrogen gas. This work demonstrates an efficient in situ assembly strategy for bimetallic oxide electrocatalysts, which can improve the electrocatalytic reduction of nitrogen to ammonia at ambient temperature and pressure.