An official website of the United States government
Thermal chemical synthesis of conjugated polymers has often been plagued by low product yields, by-product contamination and high-cost catalysts. Electrochemical synthesis is an alternative strategy that can overcome these failures to obtain highly efficient syntheses. Herein, we present the study of diketopyrrolopyrrole-bisthiophene (DPPT 2 ), diketopyrrolopyrrole-bisfuran (DPPF 2 ) and thienothiadiazole-bisthiophene (TTDT 2 ) for diblock copolymerization with terthiophene (T 3 ) as a π-linker to form tunable narrow band gap polymers. The polymers suspended as thin films have similar redox characteristics to the monomers with potential shifts that prove the identity of the respective polymers. Electrochemical impedance measurements were carried out in the −0.6 V to 1.0 V potential range with an average electron transport resistance ( R e ) value of 110 Ω irrespective of the applied potential. This confirms the polymers to have higher intrinsic electrical conductivity. The atomic ratios of the synthesized materials were calculated experimentally using energy dispersive X-ray (EDX) analysis, and they confirm the theoretical composition of the polymers. These doped polymers exhibit absorption bands in the visible to SWIR region (800–1800 nm) with optical band gaps from 0.773 to 1.178 eV in both the solid and the solution state.
more »
« less
Efficient Electrocatalytic Switching of Azoheteroarenes in the Condensed Phases
Azo-based photoswitches have shown promise as molecular solar-thermal (MOST) materials due to their ability to store energy in their metastable Z isomeric form. The energy is then released, in the form of heat, upon photoisomerization to the thermodynamically stable E form. However, obtaining a high energy density and recovering the stored energy with high efficiency requires the materials to be employed in the condensed phase and display a high degree of Z to E switching, both of which are challenging to engineer. Here, we show that arylazopyrazole motifs undergo efficient redox-induced Z to E switching in both the solution and the condensed phase to a higher completeness of switching than achieved photochemically. This redox-initiated pathway lowers the barrier of Z to E isomerization by 27 kJ/mol, while in the condensed phase, the efficiency of electrochemical switching is improved by over an order of magnitude relative to that in the solution state. The influence of the photoswitch's phase, electrical conductivity, and viscosity on the electrochemical switching in the condensed phase is reported, culminating in a set of design rules to facilitate further investigations. We anticipate the use of an alternative stimulus to light will facilitate the application of MOST materials in situations where phototriggered heat release is unachievable or inefficient, e.g., indoor or at night. Furthermore, exploiting the electrocatalytic mechanism, whereby a catalytic amount of charge triggers Z to E switching via a redox process, bypasses the need for fine tuning of the photoswitching chromophore to achieve complete Z to E switching, thus providing an alternative approach to photoswitch molecular design.
more »
« less
- Award ID(s):
- 2011846
- PAR ID:
- 10506770
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 143
- Issue:
- 37
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 15250 to 15257
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Pseudocapacitors offer a unique strategy to combine the rapid charging rates of capacitors with the high energy density of batteries, potentially offering a unique solution to energy storage challenges. Bending and twisting aromatic building blocks to form contorted aromatics have emerged as a new strategy to create organic materials with unique and tunable properties. This paper studies the union between these two concepts: molecular contortion and organic pseudocapacitors. The recent development of fully organic pseudocapacitors, including high-performing devices based on perylene diimide organic redox units, introduces the added benefit of low cost, synthetic tunability, and increased flexibility. We synthesize a series of polymers by joining perylene diimide with various linkers that incorporate a helical moiety from [4]helicene to [6]helicene into the molecular backbone. We prepare three new electroactive polymers that incorporate benzene, naphthalene, and anthracene linkers and study their pseudocapacitive performance to infer key design principles for organic pseudocapacitors. Our results show that the naphthalene linker results in the most strongly coupled redox centers and displays the highest pseudocapacitance of 292 ± 47 F/g at 0.5 A/g. To understand the pseudocapacitive behavior, we synthesized dimer model compounds to further probe the electronic structure of these materials through electronic absorption spectroscopy and first-principles calculations. Our results suggest that the identity of the aromatic linker influences the contortion between neighboring perylene diimide units, the coupling between redox centers, and their relative angles and distances. We find that competing molecular design factors must be carefully optimized to generate high-performance devices. Overall, this study provides key insights into molecular design strategies for generating high-performing organic pseudocapacitor materials.more » « less
-
null (Ed.)Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes that are vital for improving energy utilization efficiency and mitigating the aggravating global warming challenge. The noble metals such as platinum are generally the most frequently used electrocatalysts to drive these reactions and facilitate the relevant energy conversion processes. The high cost and scarcity of these materials pose a serious challenge for the wide-spread adoption and the sustainability of these technologies in the long run, which have motivated considerable efforts in searching for alternative electrocatalysts with reduced loading of precious metals or based entirely on earth-abundant metals. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts, such as high activity, selectivity, stability, maximized atom utilization efficiency and easy separation from reactants/products. The graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts for various electrochemical energy conversion processes. In this review, we highlight the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities.more » « less
-
The storage of electric energy in a safe and environmentally friendly way is of ever-growing importance for a modern, technology-based society. With future pressures predicted for batteries that contain strategic metals, there is increasing interest in metal-free electrode materials. Among candidate materials, nonconjugated redox-active polymers (NC-RAPs) have advantages in terms of cost-effectiveness, good processability, unique electrochemical properties, and precise tuning for different battery chemistries. Here, we review the current state of the art regarding the mechanisms of redox kinetics, molecular design, synthesis, and application of NC-RAPs in electrochemical energy storage and conversion. Different redox chemistries are compared, including polyquinones, polyimides, polyketones, sulfur-containing polymers, radical-containing polymers, polyphenylamines, polyphenazines, polyphenothiazines, polyphenoxazines, and polyviologens. We close with cell design principles considering electrolyte optimization and cell configuration. Finally, we point to fundamental and applied areas of future promise for designer NC-RAPs.more » « less
-
Bubbles play a ubiquitous role in electrochemical gas evolution reactions. However, a mechanistic understanding of how bubbles affect the energy efficiency of electrochemical processes remains limited to date, impeding effective approaches to further boost the performance of gas evolution systems. From a perspective of the analogy between heat and mass transfer, bubbles in electrochemical gas evolution reactions exhibit highly similar dynamic behaviors to them in the liquid–vapor phase change. Recent developments of liquid–vapor phase change systems have substantially advanced the fundamental knowledge of bubbles, leading to unprecedented enhancement of heat transfer performance. In this Review, we aim to elucidate a promising opportunity of understanding bubble dynamics in electrochemical gas evolution reactions through a lens of phase change heat transfer. We first provide a background about key parallels between electrochemical gas evolution reactions and phase change heat transfer. Then, we discuss bubble dynamics in gas evolution systems across multiple length scales, with an emphasis on exciting research problems inspired by new insights gained from liquid–vapor phase change systems. Lastly, we review advances in engineered surfaces for manipulating bubbles to enhance heat and mass transfer, providing an outlook on the design of high-performance gas evolving electrodes.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/jacs.1c06359
