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

Stabilizing specific intermediates to produce CH4 remains a main challenge in solar‐driven CO2 reduction. Herein, g‐C3N4 is modified with saturated and lacunary phosphotungstates (PWx, x = 12, 11, 9) to tailor the CO2 reduction pathway to yield CH4 in high selectivity. Increased lacuna of phosphotungstates leads to higher CH4 yield and selectivity, with a superior CH4 selectivity of 80% and 40.8 μmol·g‐1·h‐1 evolution rate for PW9/g‐C3N4. Conversely, g‐C3N4 and PWx alone show negligible CH4 production. The conversion of CO2 to CH4 follows a tandem catalytic process. CO2 is initially activated on g‐C3N4 to form *CO intermediates, meanwhile photogenerated electrons derived from g‐C3N4 transfer to PWx. Then the reduced PWx captures *CO, which is subsquently hydrogenated to CH4. With the injection of two photogenerated electrons, PW9 is capable of adsorbing and activating *CO. However, the reduced PW12 and PW11 are incapable of adsorbing *CO due to the small energy of occupied molecular orbitals, which is the reason for the poorer activity of PWx/g‐C3N4 (x = 12, 11) compared with that of PW9/g‐C3N4. This work provides new insights to regulate highly selective CO2 photoreduction to CH4 by utilizing lacuna of polyoxometalates to enhance the interaction of metals in polyoxometalates with key intermediates.