In general, if POM-based materials have high photocatalytic activity in the CO2RR process, the HOMO energy level potential of POMs is more negative than that of the product/CO2. At the same time, the LUMO energy level potential of POMs is higher than that of O2/H2O. Figure (a) provides some classical POMs energy gap, HOMO and LUMO energy potential information. Like water splitting, CO2RR is also an effective way to promote energy transformation and alleviate the energy crisis. Figure provides the application of photo/electrocatalysis of POM-based materials. "Mixed-addendum polyoxometalate" also attracts the interest of scholars. Mixed-addendum POM refers to the presence of two or more coordination atoms in a metal oxygen group. In recent years, Li's group has constructed some POMbased materials with novel structures through mixed-addendum POM. Based on density functional theory, they compared the electronic structures of [Nb3P2W15O62] 9-and [Ta3P2W15O62] 9-et al. As shown in Figure (c), the Mulliken charge distributions of the three polyanions are pretty different. Their Lewis bases are O(Ta)>O(Nb)>O(V). In addition, the mixed-addendum POMs have suitable reactivity and structural stability compared with lacunary POMs. Thus, the charge number, electrochemical performance, photochemical and photocatalytic properties of mixed-addendum POM can be adjusted by changing the proportion and type of coordination atoms. Figure (a) Some classical POMs energy gap, HOMO and LUMO energy potential information. Reproduced with permission. Copyright 2021, Elsevier. (b) The application of photo/electrocatalysis of POM-based materials. Reproduced with permission. Copyright 2021, John Wiley and Sons. (c) Molecular Electrostatic Potentials of {M3W15} (M=Ta, Nb, V) in the top view (top) and the side view (bottom) and the calculated Mulliken charges of the terminal (Ot) and bridging (Ob) oxo ligands based on DFT calculations. Reproduced with permission. Copyright 2020, John Wiley and Sons.