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[Display omitted] • The low-cost Cu 2 O/g-C 3 N 4 heterojunction is constructed by simple hydrothermal method. • Cu 2 O/g-C 3 N 4 exhibited synergistic effects of thermalcatalysis and photocatalysis. • The overpotential reduce by 0.34 V in ILs than KHCO 3 electrolyte. • We provided strategy of CO 2 reduction to ethanol assisted by ILs under thermal field. Photocatalytic CO 2 reduction is a potential way to address simultaneously environmental pollution and energy shortage. However, the difficulties of CO 2 activation and C C coupling lead to quite low conversion efficiency of CO 2 to C2 products. In this study, we constructed Cu 2 O/g-C 3 N 4 heterojunction for photocatalytic CO 2 reduction to ethanol by coupling thermal field and ionic liquids (ILs). The ethanol rate reached 0.71 mmol·g−1·h−1 over Cu 2 O/g-C 3 N 4 under photothermalcatalysis, which is 1.89 times that of photocatalysis and 7.05 times that of thermal catalysis. The temperature enhanced thermal motion of the radical, which promotes the formation of ethanol through the ·CH 3 dimerization. The 1-aminopropyl-3-methylimidazolium bromide ILs shows superior CO 2 reduction performance with a high current density (21.3 mA·cm−2) than KHCO 3 electrolyte (12.8 mA·cm−2). The overpotential is reduced by 0.34 V, which accelerates CO 2 reduction by reducing polarization. It is found that the ILs played a key role in suppressing H 2 O reduction and increasing ethanol yield in this photothermalcatalytic strategy. [ABSTRACT FROM AUTHOR]