High‐Selectivity Tandem Photocatalytic Methanation of CO₂ by Lacunary Polyoxometalates‐Stabilized *CO Intermediate

Abstract Stabilizing specific intermediates to produce CH 4 remains a main challenge in solar‐driven CO 2 reduction. Herein, g‐C 3 N 4 is modified with saturated and lacunary phosphotungstates (PW x , x =12, 11, 9) to tailor the CO 2 reduction pathway to yield CH 4 in high selectivity. Increased lacuna of phosphotungstates leads to higher CH 4 yield and selectivity, with a superior CH 4 selectivity of 80 % and 40.8 μmol ⋅ g −1 ⋅ h −1 evolution rate for PW 9 /g‐C 3 N 4 . Conversely, g‐C 3 N 4 and PW x alone show negligible CH 4 production. The conversion of CO 2 to CH 4 follows a tandem catalytic process. CO 2 is initially activated on g‐C 3 N 4 to form *CO intermediates, meanwhile photogenerated electrons derived from g‐C 3 N 4 transfer to PW x . Then the reduced PW x captures *CO, which is subsquently hydrogenated to CH 4 . With the injection of two photogenerated electrons, PW 9 is capable of adsorbing and activating *CO. However, the reduced PW 12 and PW 11 are incapable of adsorbing *CO due to the small energy of occupied molecular orbitals, which is the reason for the poorer activity of PW x /g‐C 3 N 4 ( x =12, 11) compared with that of PW 9 /g‐C 3 N 4 . This work provides new insights to regulate highly selective CO 2 photoreduction to CH 4 by utilizing lacuna of polyoxometalates to enhance the interaction of metals in polyoxometalates with key intermediates.