Hollow nanoreactors show great potential in catalysis due to the void-confine-ment effect. Yet few studies have investigated the void-confinement effect of hollow nanoreactors on intermediates. Herein, electrochemical NO reduction to NH₃ (ENOR) is used as a probe reaction to study the void-confinement effect of hollow Cu₂O@CoMn₂O₄ nanoreactors on intermediates. Com-bined with the results of catalytic activity, H₂-treated in situ diffusion Fourier transform infrared spectroscopy and the finite-element method simulation confirm that the void-confinement effect on the intermediate is the main reason for enhanced ENOR efficiency. Additionally, theoretical calculations also show that the Cu sites of Cu₂O@CoMn₂O₄ nanoreactors are favorable for the formation of *NOH intermediates. This work not only gives an insight into void-confinement effect of hollow nanoreactors on intermediates but also provides a valuable strategy for improving ENOR.