Hybrid Porous Polymers Combination of Octavinylsilsesquioxane/Pyrene with Benzothiadiazole Units for Robust Energy Storage and Efficient Photocatalytic Hydrogen Production from Water

We investigated the performance that is improved in various applications through molecular structural alterations. Specifically, we emphasized the importance of controlling the branching densities of organic moieties as a useful tactic for varying the surface area and porosity of hybrid porous organic/inorganic polymers (HPPs), which include octavinylsilsesquioxane (OVS) units. This study shows that adjusting the branching densities could greatly enhance energy storage and hydrogen production. The two-branched chemical structure (4,7-dibromo-2,1,3-benzothiadiazole, BT-Br₂) and the four-branched organic compound (1,1,2,2-tetrakis(4-bromophenyl)ethylene, TPE-Br₄) are individually reacted with OVS and 1,3,6,8-tetrabromopyrene (Py-Br₄) twice to prepare the HPPs. These materials with high or low cross-linking density, as well as small and large surface areas, are synthesized by this dual reaction, which also produces HPPs with different cross-linking densities. Based on Brunauer-Emmett-Teller calculations, the OVS-Py-BT HPP has more than 4.5 times larger surface area than the OVS-Py-TPE HPP material. Remarkably, OVS-Py-BT HPP exhibited exceptional results for supercapacitor applications, with specific capacitance values of 248 and 54 F/g for OVS-Py-BT and OVS-Py-TPE HPPs, respectively, as determined by galvanostatic charge-discharge. OVS-Py-BT HPP significantly outperformed OVS-Py-TPE HPP in photocatalytic hydrogen evolution. This is evident from their respective hydrogen evolution rates: 1348 μmol g^-1 h^-1 for OVS-Py-BT HPP and a much lower 11.3 μmol g^-1 h^-1 for OVS-Py-TPE HPP.