The clean energy transition is underway, and polymers underlie many of the technologies enabling the transition. Plastics feature prominently in applications ranging from energy generation, e.g., plastic solar cells, to energy storage, i.e., batteries with solid polymer electrolytes. Furthermore, their unique combinations of material properties, such as high strength while remaining lightweight, enable their use as composite materials in the energy production industry (e.g., as windmill blades), in the transportation sector to improve energy efficiency, or in the construction industry for intelligent materials to improve building energy conversion.
At the same time, the transition to clean energy is being aided by efforts to reduce unnecessary single-use plastics production alongside new approaches to produce and recycle polymers. These paired efforts aim to minimize society’s reliance on nonrenewable feedstocks and reduce plastics-associated energy consumption.
Indeed, polymers are helping to enable the clean energy transition, and researchers worldwide are expanding the science, technology, and applications of polymers. This is no more evident than in this Virtual Special Issue, titled Polymers for the Clean Energy Transition, which features papers on the topic, published by leading researchers in the field. This collection of articles published in JACS Au highlights the vital role and impact polymers will play as the clean energy transition unfolds.
Polymers Electrified
Organic photovoltaics (OPVs) represent one of the most promising applications of polymers to enable renewable energy. Polymer-based OPVs have improved dramatically since their inception and continue to evolve as the technology matures. One challenge with bulk heterojunction polymer-based OPVs is long-term stability, which can be compromised by many issues. Gu and co-workers [DOI: 10.1021/jacsau.4c00631] investigated the role of thermal stresses on the long-term stability of PM6/Y6, an OPV with high power conversion efficiency, using flash DSC. While maintaining a temperature below the glass transition temperature of the blend helps to ensure morphological stability, other molecular processes, such as cold crystallization of one component, can lead to a loss in device performance. One of the most significant advances in solar cell technology has been the emergence of perovskite solar cells, which have a power conversion efficiency that rivals silicon-based solar cells. Like polymer-based OPVs, perovskite solar cells also suffer from long-term stability issues. In a Perspective, Hu and co-workers [DOI: 10.1021/jacsau.4c00615] discussed how polymers, with their unique and tunable properties, can enhance the performance and stability of perovskite solar cells. For instance, polymers may be used as additives to improve light adsorption and film formation of perovskite solar cells. The Perspective concluded with an outlook for future advances of the technology.
Polymer semiconductors, including thermoelectrics and electrochromic materials, are important for the clean energy transition. Thermoelectric materials can help convert waste heat into energy, thereby improving energy efficiency in numerous applications, including residential and commercial buildings. In a Perspective, Lei and co-workers [DOI: 10.1021/jacsau.4c00638] comprehensively surveyed the current fundamental understanding of charge transport in polymer thermoelectric materials and highlighted emerging applications. To enhance the charge transfer between polymer and dopant in a polymer-based thermoelectric, Di and co-workers [DOI: 10.1021/jacsau.4c00567] developed a unique photoexcitation-assisted molecular doping approach, in which light was used to induce electron transfer. The approach improved the electrical conductivity by 4 orders of magnitude for a PDPP4T-based thermoelectric. Relatedly, electrochromic polymers enable energy conservation by regulating light transmission and heat flow in smart windows and related devices. Technology adoption and market penetration of smart windows are hindered by limited transparency and contrast issues. To overcome this challenge, Mei and co-workers [DOI: 10.1021/jacsau.4c00254, utilized meta-conjugated linkers and aromatic moieties along a polymer backbone to create a novel electrochromic polymer. The new electrochromic polymer had an optical contrast exceeding 93% and stability over 5000 cycles.
Microporous Polymers
Yang, Xu, and co-workers [DOI: 10.1021/jacsau.4c00565] developed a sulfonated microporous polyxanthene electrode binder with enhanced chemical stability. The binder performance enhancement was a trifecta: 1) reduced adsorption of ionomer atop Pt surface, 2) prevented phosphoric acid loss, and 3) promoted gas transport within the catalyst layer. Using the binder significantly improved the performance of high-temperature hydrogen fuel cells. Beyond electrode binders, microporous polymers have many advantages for clean energy, including photocatalysis and membrane separations. In another example, Kuo and co-workers [DOI: 10.1021/jacsau.4c00537] demonstrated using conjugated microporous polymer for enhanced CO2 uptake and energy storage. In particular, the dihydroxyterephthalaldehyde-based conjugated microporous polymers featured a high BET surface area (∼431 m2 g–1), which enabled a CO2 capture capacity of 1.85 mmol g–1 and a specific capacitance of 121 F g–1 at 0.5 g–1.
Polymer Upgrading and Processing
Polymer upcycling, in which low-value plastic waste is converted into high-value plastic for additional use, is an approach to extend the useful lifetime of a material, thereby reducing plastic waste and energy consumption. The sulfonation of waste aromatic polymers, such as polystyrene, is particularly interesting for creating electrically active plastics. In this collection, Kayser and co-workers [DOI: 10.1021/jacsau.4c00355] developed a sulfonation method capable of achieving a high degree of sulfonation with no side reactions using a sulfonic acid–base ionic liquid. The approach can sulfonate polystyrene up to 92%. In a demonstration of upcycling, sulfonated waste polystyrene was integrated into an organic electrochemical transistor, which showed performance consistent with devices using neat, nonwaste polystyrene. Finally, hierarchically structured carbon materials may be used in various applications ranging from energy conversion to storage. However, the production of structured carbon remains a challenge. In a Perspective, Lu, DeSimone, and co-workers [DOI: 10.1021/jacsau.4c00555] reviewed the challenges and opportunities of merging additive manufacturing and pyrolysis to produce structured carbon. The Perspective discussed the effects of chemistry, additives, and pyrolysis conditions on the resulting carbon structure. By combining the continuous liquid interface production vat photopolymerization with pyrolysis, the future of new structures and technologies is bright.
As the above collection of articles in this Virtual Special Issue demonstrates, polymers will play a diverse and important role in the clean energy transition. They will touch nearly every aspect of the clean energy transition from energy generation to energy storage to improving energy efficiency. Relatedly, new science and technology will reduce the energy required to produce polymers and extend their useful lifetime. Taken together, we remain in a plastic age. With correct societal management (as INC-5 negotiations [https://www.unep.org/inc-plastic-pollution/session-5], toward an international agreement on plastic pollution, draws to a close), plastics can transform from a material known primarily as a “throwaway” material toward a class of materials that will enable a new age, i.e., the age of clean energy.
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.