The electrochemical nitrogen reduction reaction (ENRR), as a promising green N2 fixation strategy for the production of ammonia under ambient conditions, has attracted significant attention. Herein, we report the synthesis of copper nanocrystals anchored on a carbonized corn gel (Cu NCs/CCG) for electrochemical N2 fixation to NH3, in which the rich O-containing functional groups on CCG are beneficial for efficiently dispersing and stabilizing the copper nanocrystals. As a result, the obtained Cu NCs/CCG achieve a high faradaic efficiency (FE) of 25.89% and a large NH3 yield rate of 1514 μg h−1 mgCu−1 at −0.3 V versus an RHE in 0.1 M Na2SO4. Moreover, the Cu NCs/CCG demonstrate good ENRR stability and durability. This work paves the way for developing high-performance ENRR electrocatalysts utilizing biomass derivatives as precursors for NH3 synthesis.