<p>The construction of carbon‒nitrogen (C‒N) bonds is an essential transformation for synthesizing value-added organonitrogen compounds, including the raw materials for fertilizers, synthetic materials and pharmaceuticals. Electrocatalytic C‒N bond construction has emerged as an alternative strategy to traditional thermochemical routes, avoiding harsh and energy-intensive processes. This protocol describes an electrocatalytic C‒N bond construction strategy to synthesize organonitrogen from nitrogen oxides in water under ambient conditions, with a focus on several vital chemicals, such as urea, formamide, cyclohexanone oxime, amino acids and ¹⁵N-labeled amino acids. Here, we provide detailed procedures for catalyst and reaction device design, electrosynthesis, product quantification and measurements for investigating the reaction mechanisms. Four catalysts, namely, vacancy-rich ZnO, core-shell Cu@Zn, AgRu alloy and low-coordination Ag, are synthesized as cathode catalysts. Two types of electrolyzers, an H-type cell and a flow cell, are used for the electrocatalytic reaction. Characterization techniques such as electrochemical in situ Raman spectroscopy, in situ attenuated total reflectance–Fourier transform infrared spectroscopy, ex situ electron paramagnetic resonance and scanning flow cell-differential electrochemical mass spectrometry have been adopted to study the reaction mechanism. The synthesis amount of urea is at the micromole level, while the synthesis amounts of formamide, cyclohexanone oxime and amino acids are at the millimole level. The catalyst synthesis protocol requires 0.5–1.5 d, the electrosynthesis requires ≤11 h and the in situ characterization requires 0.5–1.5 h.</p>