Suppressing S‐Scheme Charge Transfer in Type‐I Band‐Aligned Heterojunctions by Semimetallic Bismuth for Boosting Photothermal‐Enhanced CO ₂ Photoreduction to CH ₄ in Pure Water

ABSTRACT S‐scheme charge transport enables spatial separation of photogenerated carriers in type‐I band‐aligned heterojunctions, but at the cost of recombining a fraction of electrons and holes. Herein, we demonstrate that inserting semimetallic Bi at the heterointerface between Cu 2‐x S core and TD‐COF shell effectively suppresses S‐scheme charge transfer in a Cu 2‐x S@TD‐COF heterojunction without altering the redox potentials of active carriers, thereby enhancing CH 4 photosynthesis from CO 2 and H 2 O by 3.9‐fold. The incorporated Bi functions as a “charge relay” that facilitates barrier‐free transport of photoelectrons along the Cu 2‐x S→Bi→TD‐COF pathway and holes in the opposite direction, thus preventing S‐scheme recombination between Cu 2‐x S electrons and TD‐COF holes. Concurrently, Bi serves as a “light‐to‐heat converter” that improves the photothermal response of the heterojunction, further accelerating charge separation, promoting activation of CO 2 and H 2 O molecules, and reducing energy barriers for CO 2 methanation and H 2 O oxidation. Consequently, the engineered Cu 2‐x S/Bi@TD‐COF heterojunction delivers a remarkable CH 4 production rate of 592.8 µmol g cat −1 h −1 with 99.6% selectivity, outperforming previously reported photothermal catalysts, and attaining a record‐high apparent quantum efficiency of 3.1% at 808 nm. This work unveils fundamental mechanistic insights into semimetal‐mediated charge transfer processes and establishes a rational design paradigm for high‐performance near‐infrared‐responsive type‐I band‐aligned heterostructured photocatalysts.