Organic Energy Molecules
Development of Nanostructured Materials for Energy Storage, Conversion and Photocatalysis


Our strategy in the development of novel materials for energy storage and conversion focuses on conjugated polymer and carbons controlling morphological aspects that include surface area, pore size and pore volume; connectivity and percolation; solubility and dispersability. We utilize simple organic reactions to modify sustainable carbon materials and establish methodologies that can enhance properties such as electron and ion conductivity. Another important aspect relates to designing materials that are photoactive and can therefore be used as photocatalysts for applications in the topical field of solar fuels. In this regard, we focus on controlling the absorption and the electronic levels of conjugated microporous polymers and related materials.



    Interest in the production of functional materials from renewable resources has caught much attention due to the growing concern for sustainable energy and resources. To date, the department has produced variety of functional carbon materials in the fields of catalysis,
    3 lithium ion battery,3a adsorption/heavy metal chelation,4 and supercapacitors5 by utilizing the HTC process. With aims to further expand the potential of HTC-derived carbon materials, my group explores post-modification methods which could offer novel carbon materials with more diverse functionalities. Our initial studies confirmed that surface modification HTC-derived carbons were possible by applying conventional organic reactions as shown in Figure 1 below.


    HTC

    Figure 1. Summary of different types of reactions that were carried out using HTC-derived carbon as a reaction platform; a) Diels-Alder cycloaddition, b) epoxidation and the subsequent ring opening of epoxides, 3) electrophilic aromatic substitution (aryldiazoniums), 4) bromination and the subsequent cross-coupling reactions, 5) oxidation reactions using KPS or H
    2SO4/HNO3 and the subsequent amidation or esterification reactions, 6) addition of RAFT CTA and the subsequent RAFT polymerization


    These reactions were carried out on both the HTC material prepared at high and low temperatures. Once these initial reactions and its substrates were screened, we shifted to transformations and substrates that could become useful for future applications. The four types of surface modifications were made with an aim to; 1) introduce thiol groups on the carbon surface; 2) bias the conductivity of HTC-derived carbons by attachment of donor/acceptor molecules; 3) enable Reversible Addition−Fragmentation chain Transfer (RAFT) polymerization off the carbon surfaces; 4) enhance the dispersability of HTC-derived carbons in water.


      Conjugated microporous polymers (CMPs) can be defined as amorphous porous networks that exhibit extended conjugation and are therefore related to conducting polymers.
      7 In this project, we are developing strategies to control both the electronic and morphological properties of novel CMPs, including control over their micropore structure and their physical surface area.
      In the example shown in Figure 2, varying the amount of simple templates such as silica nanoparticles as a reaction matrix, we can control the surface areas of the CMPs with the micropore size being within similar range of that of the template after its removal.

      CMP Templating

      Figure 2. Tuning porosity of the CMP shown on the right by via silica templating.

      In terms of electronic properties, a useful strategy when designing suitable conjugated building blocks for CMPs is to incorporate a chromophore with high absorbance and emission in the visible and near infrared regions into the π-conjugated systems. As a light-harvesting antenna, the chromophore is attached to an electron donor such as phenylene, thiophene or amine derivatives, and an electron acceptor such as nitrile derivatives. In Figure 3 a number of building blocks is displayed we are working on: novel chromophores such as diketopyrrolopyrrole, benzodifuranone and benzodipyrrolone are developed. Similar molecules have been attracting much interest recently.
      11 Testing includes not only CMPs, but also the use in organic field effect transistors (OFETs), for electron mobility determination, and in organic solar cells where photoactivity of the building-blocks will be assessed.


      StructuresColours


      Figure 3. Examples of building-blocks (right) and typical absorption range of antennae building-blocks in solution (left).

      By introducing conjugated building blocks with varied Donor-Acceptor moieties into the network backbone, the HOMO- and LUMO-levels and the resulting band gaps of the CMPs can be tuned as aimed. Once the morphological and electronic aspects of the CMPs are known and can be controlled, we aim to catalyse reactions such as the CO
      2 reduction using the networks as heterogeneous catalysts.


      References:

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