Photoelectronic Porous Covalent Organic Materials: Research Progress and Perspective (original) (raw)
Related papers
matic worldwide energetic crisis that we are suffering these days. In this sense, solar energy conversion plays an important role in the transition to a more suitable energy scenario. [1] During the last decades, a large number of systems have been developed to drive so-called artificial photosynthesis process being the most representative of inorganic semiconductors (ISs) and hybrid thereof. [2-4] However, we are witnessing the renaissance of organic semiconductors (OS), named as "soft photocatalyst", in the photocatalytic field. [5] The main advantage of OS versus ISs ones is that their optoelectronic and surface catalytic properties can be designed at the molecular level thankfully to the great development of organic synthetic tools nowadays available [6] which includes high-throughput techniques. [7] In general, OS photocatalyst are conjugate polymers (CPs) but conjugated porous polymers (CPPs), [8-10] a relatively new kind of crosslinked CPs in form of 2D and 3D networks, appears with force in the topic, as can be seen for the incredible number of revision found in the literature the last couple of years. [5,10-15] Also, we showed in a recent revision that their use beyond carbon nitride [16] as organic counterpart on the design of organic-inorganic hybrid (OIH) photocatalysts was growing appearing as future materials to compose OIH. [17] Furthermore, when designing a hybrid photocatalyst, an important aspect to consider is the type of charge transfer mechanism between both semiconductors. [18,19] In the particular case of an OIH, it is important to note that the band energy diagram of organic CPs is higher than the ISs. With this configuration if both semiconductors are simultaneously illuminated there are three types of charge transfer possibilities: i) Type II or p-n heterojunction; ii) direct Z-Scheme [20] (also named as S-Scheme [21]) and; iii) traditional Z-Scheme (also named as indirect, redox or conductive mediated Z-Scheme) (Figure 1a). The main difference between the direct and the indirect Z-Scheme is the presence or not of a third specie (i.e., redox pair, or even a metal as ohmic contact in all solid system [22]) which help to the photogenerated electron in the semiconductor with the lower conduction band (CB) to go to the valence band (VB) of the other semiconductor. There Phenanthrenequinone (PhQ) based Conjugated Porous Polymers (CPPs) are synthetized without and with the presence of fluorine atoms in the trisubstituted core benzene unit (CPP-FPA and CPP-PA). Furthermore, organicinorganic hybrid heterojunctions based on these CPPs and TiO 2 as inorganic semiconductor are prepared (CPP-FPA@T-10 and CPP-PA@T-10, with the polymer loading ≈10 wt.%). The photonic efficiency for H 2 photoproduction is 33% higher when the CPP has fluorine atoms. This enhancement is even higher in presence of 1 wt.% platinum as co-catalyst. Thus, the Pt/ CPP-FPA@T-10 hybrid (≈31.7 mmol g-1 h-1 and 11.7% of photonic efficiency) presents H 2 production nearly twice than that of the nonfluorinated hybrid Pt/CPP-PA@T-10 (≈16.6 mmol g-1 h-1 and 6.1% of photonic efficiency) and 3.5-times higher than that of the Pt/TiO 2 (≈8.9 mmol g-1 h-1 and 3.29% of photonic efficiency) photocatalyst. Charge dynamics studies show that both hybrid heterojunctions exhibit a direct Z-scheme charge transfer mechanism, and the presence of fluorine atoms in the CPP structure leads to an increasing charge separation lifetime which is in accordance with the better performance in H 2 production. These findings on fluorine doping provide essential clues for the design of structure electronic engineered CPPs for energy conversion and storage technologies.
Recent Advances on Porous Materials for Synergetic Adsorption and Photocatalysis
ENERGY & ENVIRONMENTAL MATERIALS, 2021
Porous photocatalysts are promising materials capable of simultaneously adsorbing and oxidizing/reducing target species, showing great potentials in environmental remediation and energy generation. This review offered a comprehensive overview of the recent progress in design, fabrication, and applications of porous photocatalysts, including carbon-based semiconductors, metal oxides/sulfides, metal-organic frameworks, and adsorbent-photocatalyst hybrids. The fundamental understanding of the structure-performance relationships of porous materials together with the in-depth insights into the synergetic effects between adsorption and photocatalysis were presented. The strategies to further improve the photocatalytic activity of porous photocatalysts were proposed. This review would provide references and outlooks of constructing efficient porous materials for adsorptive and photocatalytic removal of pollutants and energy production.
Our program on capacitive energy storage is a comprehensive one that combines experimental and computational components to achieve a fundamental understanding of charge storage processes in redox-based materials, specifically transition metal oxides. Some of the highlights of this program are the identification of intercalation pseudocapacitance in Nb2O5, which enables high energy density to be achieved at high rates, and the development of a new route for synthesizing mesoporous films in which preformed nanocrystal building blocks are used in combination with polymer templating. The resulting material architectures have large surface areas and enable electrolyte access to the redox active pore walls, while the interconnected mesoporous film provides good electronic conductivity. Select first-principles density-functional theory studies of prototypical pseudocapacitor materials are reviewed, providing insight into the key physical and chemical features involved in charge transfer and ion diffusion. Rigorous multiscale physical models and numerical tools have been developed and used to reproduce electrochemical properties of carbon-based electrochemical capacitors with the ultimate objective of facilitating the optimization of electrode design. For the organic photovoltaic (OPV) program, our focus has been ongoing beyond the trial-and-error Edisonian approaches that have been responsible for the increase in power conversion efficiency of blend-cast (BC) bulk heterojunction blends of polymers and fullerenes. Our first approach has been to use molecular self-assembly to create the ideal nanometer-scale architecture using thermodynamics rather than relying on the kinetics of spontaneous phase segregation. We have created fullerenes that self-assemble into one-dimensional stacks and have shown that use of these self-assembled fullerenes lead to dramatically enhanced OPV performance relative to fullerenes that do not assemble. We also have created self-assembling conjugated polymers that form gels based on electrically continuous cross-linked micelles in solution, opening the possibility for water-processable “green” production of OPVs based on these materials. Our second approach has been to avoid kinetic control over phase separation by using a sequential processing (SqP) technique to deposit the polymer and fullerene materials in separate deposition steps. The polymer layer is deposited first, using solvents and deposition conditions that optimize the polymer crystallinity for swelling and hole mobility. The fullerene layer is then deposited in a second step from a solvent that swells the polymer but does not dissolve it, allowing the fullerene to penetrate into the polymer underlayer to the desired degree. Careful comparison of composition- and thickness-matched BC and SqP devices shows that SqP not only produces more efficient devices but also leads to devices that behave more consistently.
Molecular Porous Photosystems Tailored for Long‐Term Photocatalytic CO 2 Reduction
Angewandte Chemie, 2020
Herein, we report the molecular-level structuration of two full photosystems into conjugated porous organic polymers. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyse the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long-term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in-situ ultrafast time-resolved spectroscopy.
Energies
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two innovative classes of porous coordination polymers. MOFs are three-dimensional materials made up of secondary building blocks comprised of metal ions/clusters and organic ligands whereas COFs are 2D or 3D highly porous organic solids made up by light elements (i.e., H, B, C, N, O). Both MOFs and COFs, being highly conjugated scaffolds, are very promising as photoactive materials for applications in photocatalysis and artificial photosynthesis because of their tunable electronic properties, high surface area, remarkable light and thermal stability, easy and relative low-cost synthesis, and structural versatility. These properties make them perfectly suitable for photovoltaic application: throughout this review, we summarize recent advances in the employment of both MOFs and COFs in emerging photovoltaics, namely dye-sensitized solar cells (DSSCs) organic photovoltaic (OPV) and perovskite solar cells (PSCs)...