Role of Hydrogen Radical in Ultrasound‐Assisted Electroreduction of Low‐Concentration CO 2 to CH 4 Over Single‐Atom Cu Catalyst

ABSTRACT Electrochemical reduction of low‐concentration CO 2 to CH 4 is promising for mitigating emissions and producing chemicals, but mass transfer in CO 2 reduction reaction (CO 2 RR) and the challenge of *CO intermediate alkylation hinder high current densities. Herein, we demonstrate that ultrasound assistance at 50 000 Hz significantly boosts the electroreduction of low‐concentration CO 2 to CH 4 over a single‐atom Cu catalyst. Characterization techniques indicate that copper is in an atomic dispersion state in the catalyst, and the coordination situation is a typical Cu─N 4 structure. Under ultrasonic activation, the Faradaic efficiency of CH 4 surges from 7% to 83%, current density is 920 mA cm −2 , yielding a record‐high electroproduction rate of 0.686 µmol s −1 cm −2 . Isotope‐labeled 13 CO 2 experiments verify the CO 2 origin of CH 4 , and the catalyst maintains stable performance for 12 h. In situ Raman spectroscopy identifies *CO and *CH intermediates, while electron paramagnetic resonance confirms ultrasonic generation of hydrogen radicals (·H). Theoretical calculations reveal that ·H preferentially binds to the C atom of *CO compared with interaction at O site, driving thermodynamically favorable CH 4 formation.