A Strategy for Breaking Polyoxometalate-based MOFs To Obtain High Loading Amounts of Nanosized Polyoxometalate Clusters to Improve the Performance of Dye-sensitized Solar Cells

Polyoxometalates (POM) have already been confirmed to act as effective electron-transfer mediators for improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) based on previous studies. However, the improvement may be limited by the agglomeration of the polyoxoanions. In this paper, the previous synthesis strategy is improved upon by breaking the metal-organic frameworks (MOFs) with POMs as the secondary building units ([Ni(bpp)(H2O)2]3[P2W18O62]⋅24 H2O (1) (bpp=1,3-bis(4-pyridyl)propane) and H6[Cu3(H2O)6(P2W18O62)2(3-dpye)6]⋅28 H2O (2) (3-dpye=N,N′-bis(3-pyridinecarboxamide)-1,2-ethane)) to design and synthesize small sized and highly disperse POM nanoparticles by means of compositing with TiO2, through calcination to remove the organic ligand. TEM and element mapping confirm that P2W18O626− (denoted as P2W18) nanoparticles with the diameter of ≈1 nm are uniformly distributed in TiO2 composites. The loading amount (wt. %) of POM in MOFs reaches 75.67 %. The small sized and highly disperse P2W18 nanoparticles may provide more active sites and specific surface areas for improving the PCE of DSSCs. Finally, the investigations indicate that the PCE of composite P2W18⋅NiO@TiO2 photoanodes is up to 7.56 %, which was 26 % higher than the pristine TiO2 based photoanodes.