Abstract

Abstract Photosynthetic conversion of CO 2 into fuel and chemicals is a promising but challenging technology. The bottleneck of this reaction lies in the activation of CO 2 , owing to the chemical inertness of linear CO 2 . Herein, we present a defect‐engineering methodology to construct CO 2 activation sites by implanting carbon vacancies (CVs) in the melon polymer (MP) matrix. Positron annihilation spectroscopy confirmed the location and density of the CVs in the MP skeleton. In situ diffuse reflectance infrared Fourier transform spectroscopy and a DFT study revealed that the CVs can function as active sites for CO 2 activation while stabilizing COOH* intermediates, thereby boosting the reaction kinetics. As a result, the modified MP‐TAP‐CVs displayed a 45‐fold improvement in CO 2 ‐to‐CO activity over the pristine MP. The apparent quantum efficiency of the MP‐TAP‐CVs was 4.8 % at 420 nm. This study sheds new light on the design of high‐efficiency polymer semiconductors for CO 2 conversion.