Precision Molecular Engineering of Carbon Nitride for Efficient and Selective Photoreduction of CO₂ to C₂H₆ in Pure Water

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Photocatalytic CO 2 reduction into high‐value C 2+ products such as C 2 H 6 is of great importance but challenging due to their multi‐electron steps and high energy barrier of C─C coupling. Moreover, improving its solar‐to‐chemical (STC) energy conversion efficiency in pure water beyond the current 1% empirical value is also a significant challenge. Herein, graphite carbon nitride (g‐C 3 N 4 ) nanosheets with controllable carbon (C) doping and nitrogen (N) vacancies (PCCN‐x) are designed through a biochar‐tailored protocol for efficiently and selectively photo‐converting CO 2 into C 2 H 6 . The optimal PCCN‐10 photocatalyst enables the achievement of an exceptional C 2 H 6 activity of 99.14 µmol g −1 h −1 with C 2 H 6 selectivity of 80.33% over 20 h in pure water. A record STC efficiency of ≈1.13% for solar fuel production from CO 2 and H 2 O vapor is also achieved without any other energy inputs. Outdoor tests also demonstrated an impressive CO 2 ‐to‐C 2 H 6 photo‐conversion rate of 43.17 µmol g −1 h −1 in pure water, with stable activity over 50 h period. Critically, experimental and theoretical calculations further confirm the pivotal role of bridged C sites and N vacancies in activating CO 2 molecules and promoting the formation of C─C coupling intermediate ( * OCCO), which is very beneficial for the production of C 2 H 6 . The impressive performance of this work in the photocatalytic conversion of CO 2 to high‐value C 2 H 6 fuels paves the way for large‐scale fuel production and broader sustainable applications.