Transforming nanoscale and bulk metals into single atoms is crucial for the scalable production of single-atom catalysts (SACs), especially during pyrolysis. However, conventional equilibrium heating approaches often require prolonged operation to decompose metal aggregates, leading to tedious and time-consuming procedures for synthesizing SACs. In this study, we introduce high-temperature shock (HTS) strategy to enhance metal atomization, achieving the direct transformation of bulk copper foil into single atoms in just 0.5 s at 1700 K. The HTS-produced Cu catalyst demonstrates a high content of 0.54 wt.%, comparable to those achieved by commonly reported top-down strategies, indicating that the HTS method provides a compelling alternative for synthesizing Cu SACs from bulk Cu precursors. Structural analysis confirmed the synthesis of a Cu–N–C SAC with a Cu–N₄ coordination environment. This Cu–N₄ structure shows excellent catalytic performance for nitrite reduction to ammonia, achieving over 90% Faradaic efficiency across the entire working potential range and an ammonia production rate of up to 11.12 mg·cm^−2·h−1 at −1.2 V vs. reversible hydrogen electrode (RHE), surpassing other reported Cu-based electrocatalysts. Furthermore, ab initio molecular dynamics (AIMD) simulations reveal that transient high temperatures not only promote the formation of thermodynamically favorable Cu–N bonds but also prevent excessive sintering and aggregation of metal atoms.