Metal oxide nanomaterials directly grown on conductive substrates are optimal electrode materials because their structures allow for rapid ion and electron transport and thereby reduce internal resistance in the electrode. The development of such binder‐free, self‐supporting electrodes is of great significance for applications in electrocatalysis. In this work, a simple hydrothermal in situ self‐assembly reaction and annealing process was developed to prepare three kinds of nickel oxide @ carbon felt (NiO@CF) nanocomposites with different morphologies. The influence of different precipitators (strong or weak bases) on the morphology of the resulting nano‐sized nickel oxide nanocomposites was investigated. The microstructures of the NiO@CF samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). When ammonia was used as the precipitator, NiO grew vertically on the surface of the carbon felt and formed a mesoporous nanosheet‐like structure (NiO NSs@CF). As an electrocatalytic nitrogen reduction reaction (e‐NRR) electrode, the NiO NSs@CF sample showed an excellent NH3 yield (71.3 μg h−1 mg−1cat.) and Faradaic efficiency (17.9 % at −0.5 V vs. RHE) in 0.1 M Na2SO4. The good performance was attributed to the vertical interleaved mesoporous sheet‐like structure (with the pore size of 15 nm and the thickness of ∼30 nm) and the relatively high concentration of oxygen vacancies. First‐principles calculations with strong on‐site Coulomb interactions demonstrated that the presence of oxygen vacancy on NiO sample leads to a significantly stronger N binding over the surface, benefiting for the nitrogen gas adsorption and reduction. The e‐NRR performance of this binder‐free, flexible electrode material is superior to that of other reported nickel‐based nanomaterials. This study highlights the potential of such binder‐free carbon felt electrodes for use in e‐NRR that could meet the needs of industrial production.

Nickel-based oxides have received extensive attention in electrocatalysis because of their cost-effective and tunable 3d orbital electronic structure; however, their research on the electrochemical nitrogen reduction reaction (e-NRR) is rarely reported. Herein, the synthesis of NiO nanospheres grown on carbon felt (NiO@CFs) is demonstrated by employing a surfactant-assisted hydrothermal reaction and high-temperature treatment. The influence of different types of surfactants on the morphology and e-NRR performance of NiO@CFs is systematically investigated. The utilization of CF as an excellent substrate for coating NiO can significantly improve the electrical conductivity and enhance the number of active sites. Furthermore, the formation of oxygen vacancies during the calcination process can help to transfer electrons into the antibonding orbitals of N2 molecules, thereby promoting N2 adsorption and activation. A typical sample NiO@CF-CTAB electrode exhibits an excellent ammonia electrosynthesis activity (NH3 yield rate: 34.21 μg·mg–1·h–1; Faradaic efficiency: 6.7%) at −0.25 V versus reversible hydrogen electrode (vs RHE) due to the regular spherical structure of NiO with a diameter of 22.4 nm, high content of Ni3+, and oxygen vacancies in samples. This research provides significant implications for the design and synthesis of a low-cost, binder-free, and highly efficient e-NRR nickel-based nanosphere electrocatalyst.