Polyacrylonitrile-b-poly(butyl acrylate) Block Copolymers as Precursors to Mesoporous Nitrogen-Doped Carbons: Synthesis and Nanostructure

Recent Advances on Nitrogen-Doped Porous Carbons Towards Electrochemical Supercapacitor Applications

Due to ever-increasing global energy demands and dwindling resources, there is a growing need to develop materials that can fulfil the World's pressing energy requirements. Electrochemical energy storage devices have gained significant interest due to their exceptional storage properties, where the electrode material is a crucial determinant of device performance. Hence, it is essential to develop 3-D hierarchical materials at low cost with precisely controlled porosity and composition to achieve high energy storage capabilities. After presenting the brief updates on porous carbons (PCs), then this review will focus on the nitrogen (N) doped porous carbon materials (NPC) for electrochemical supercapacitors as the NPCs play a vital role in supercapacitor applications in the field of energy storage. Therefore, this review highlights recent advances in NPCs, including developments in the synthesis of NPCs that have created new methods for controlling their morphology, composition, and pore structure, which can significantly enhance their electrochemical performance. The investigated N-doped materials a wide range of specific surface areas, ranging from 181.5 to 3709 m2  g-1 , signifies a substantial increase in the available electrochemically active surface area, which is crucial for efficient energy storage. Moreover, these materials display notable specific capacitance values, ranging from 58.7 to 754.4 F g-1 , highlighting their remarkable capability to effectively store electrical energy. The outstanding electrochemical performance of these materials is attributed to the synergy between heteroatoms, particularly N, and the carbon framework in N-doped porous carbons. This synergy brings about several beneficial effects including, enhanced pseudo-capacitance, improved electrical conductivity, and increased electrochemically active surface area. As a result, these materials emerge as promising candidates for high-performance supercapacitor electrodes. The challenges and outlook in NPCs for supercapacitor applications are also presented. Overall, this review will provide valuable insights for researchers in electrochemical energy storage and offers a basis for fabricating highly effective and feasible supercapacitor electrodes.

Thermal Transformation of Polyacrylonitrile Accelerated by the Formation of Ultrathin Nanosheets in a Metal-Organic Framework

In this study, polyacrylonitrile (PAN) nanosheets with unimolecular thickness were successfully synthesized by cross-linking polymerization in the 2D nanospaces of a metal-organic framework. In contrast to 1D and 3D analogues, crystallization could be inhibited by the topological constraint of the ultrathin 2D network structure, allowing for an efficient thermal transformation reaction of PAN. The amorphous nature of the PAN nanosheets led to an increase in the access of oxygen molecules to the polymer chains, facilitating the thermal dehydroaromatization reactions to yield a ladder polymer structure with a highly extended conjugated system. Notably, further carbonization of this ladder polymer afforded graphitic carbon with a highly ordered structure because of the well-defined precursor structure.

Polyacrylonitrile-b-Polystyrene Block Copolymer-Derived Hierarchical Porous Carbon Materials for Supercapacitor

The use of block copolymers as a sacrificial template has been demonstrated to be a powerful method for obtaining porous carbons as electrode materials in energy storage devices. In this work, a block copolymer of polystyrene and polyacrylonitrile (PS-b-PAN) has been used as a precursor to produce fibers by electrospinning and powdered carbons, showing high carbon yield (~50%) due to a low sacrificial block content (f_PS ≈ 0.16). Both materials have been compared structurally (in addition to comparing their electrochemical behavior). The porous carbon fibers showed superior pore formation capability and exhibited a hierarchical porous structure, with small and large mesopores and a relatively high surface area (~492 m²/g) with a considerable quantity of O/N surface content, which translates into outstanding electrochemical performance with excellent cycle stability (close to 100% capacitance retention after 10,000 cycles) and high capacitance value (254 F/g measured at 1 A/g).

Multi-scale computer-aided design and photo-controlled macromolecular synthesis boosting uranium harvesting from seawater

By integrating multi-scale computational simulation with photo-regulated macromolecular synthesis, this study presents a new paradigm for smart design while customizing polymeric adsorbents for uranium harvesting from seawater. A dissipative particle dynamics (DPD) approach, combined with a molecular dynamics (MD) study, is performed to simulate the conformational dynamics and adsorption process of a model uranium grabber, i.e., PAO_m-b-PPEGMA_n, suggesting that the maximum adsorption capacity with atomic economy can be achieved with a preferred block ratio of 0.18. The designed polymers are synthesized using the PET-RAFT polymerization in a microfluidic platform, exhibiting a record high adsorption capacity of uranium (11.4 ± 1.2 mg/g) in real seawater within 28 days. This study offers an integrated perspective to quantitatively assess adsorption phenomena of polymers, bridging metal-ligand interactions at the molecular level with their spatial conformations at the mesoscopic level. The established protocol is generally adaptable for target-oriented development of more advanced polymers for broadened applications.

Developing materials for uranium harvesting from seawater with high adsorption capacity remains challenging. Here, the authors develop a new protocol, by combining multi-scale computational simulations with the PET-RAFT polymerization, for rational design and precise synthesis of block copolymers with optimal architectures and atomic economy, achieving a capacity of 11.4 mg/g within 28 days.

Toward Green Atom Transfer Radical Polymerization: Current Status and Future Challenges

Reversible-deactivation radical polymerizations (RDRPs) have revolutionized synthetic polymer chemistry. Nowadays, RDRPs facilitate design and preparation of materials with controlled architecture, composition, and functionality. Atom transfer radical polymerization (ATRP) has evolved beyond traditional polymer field, enabling synthesis of organic-inorganic hybrids, bioconjugates, advanced polymers for electronics, energy, and environmentally relevant polymeric materials for broad applications in various fields. This review focuses on the relation between ATRP technology and the 12 principles of green chemistry, which are paramount guidelines in sustainable research and implementation. The green features of ATRP are presented, discussing the environmental and/or health issues and the challenges that remain to be overcome. Key discoveries and recent developments in green ATRP are highlighted, while providing a perspective for future opportunities in this area.

Carbon nano-onion induced organization of polyacrylonitrile-derived block star polymers to obtain mesoporous carbon materials

Herein, we report the synthesis of mesoporous carbon materials from diblock star copolymers derived from polyacrylonitrile. The size of the pores was controlled by manipulating the length of the polymer blocks. Furthermore, the organization of polymers on the carbon nano-onion's surface resulted in materials of higher surface area and superficial electrochemical performance.

Polymeric Network Hierarchically Organized on Carbon Nano-onions: Block Polymerization as a Tool for the Controlled Formation of Specific Pore Diameters

The organization of specific pores in carbonaceous three-dimensional networks is crucial for efficient electrocatalytic processes and electrochemical performance. Therefore, the synthesis of porous materials with ordered and well-defined pores is required in this field. The incorporation of carbon nanostructures into polymers can create material structures that are more ordered in comparison to those of the pristine polymers. In this study we applied polymer-templated methods of carbon material preparation, in which outer blocks of the star copolymers form the carbon skeleton, while the core part is pore-forming. Well-defined 6-star-(poly(methyl acrylate)-b-poly(4-acetoxystyrene)) dendrimers were synthesized by reversible addition-fragmentation chain-transfer polymerization. They were then transformed into poly(4-vinylphenol) derivatives (namely 6-star-(poly(methyl acrylate)-b-poly(4-vinylphenol)), subjected to polycondensation with formaldehyde, and pyrolyzed at 800 °C. Cross-linking of phenolic groups provides a polymer network that does not depolymerize by pyrolysis, unlike poly(methyl acrylate) chains. The selected star polymers were attached to carbon nano-onions (CNOs) to improve the organization of the polymer chains. Herein, the physicochemical properties of CNO-polymer hybrids, including the textural and the electrochemical properties, were compared with those of the pristine pyrolyzed polymers obtained under analogous experimental conditions. For these purposes, we used several experimental and theoretical methods, such as infrared, Raman, and X-ray photoelectron spectroscopy, nitrogen adsorption/desorption measurements, scanning and transmission electron microscopy, and electrochemical studies, including cyclic voltammetry. All of the porous materials were evaluated for use as supercapacitors.

Assemblies of Polyacrylonitrile-Derived Photoactive Polymers as Blue and Green Light Photo-Cocatalysts for Cu-Catalyzed ATRP in Water and Organic Solvents

Photoluminescent nanosized quasi-spherical polymeric assemblies prepared by the hydrothermal reaction of polyacrylonitrile (PAN), ht-PLPPAN, were demonstrated to have the ability to photo-induce atom transfer radical polymerization (ATRP) catalyzed by low, parts per million concentrations of CuII complex with tris(2-pyridylmethyl)amine (TPMA). Such photo induced ATRP reactions of acrylate and methacrylate monomers were performed in water or organic solvents, using ht-PLPPAN as the photo-cocatalyst under blue or green light irradiation. Mechanistic studies indicate that ht-PLPPAN helps to sustain the polymerization by facilitating the activation of alkyl bromide species by two modes: 1) green or blue light-driven photoreduction of the CuII catalyst to the activating CuI form, and 2) direct activation of dormant alkyl bromide species which occurs only under blue light. The photoreduction of the CuII complex by ht-PLPPAN was confirmed by linear sweep voltammetry performed under illumination. Analysis of the polymerization kinetics in aqueous media indicated even though CuI complexes comprised only 1-1.4% of all Cu species at equilibrium, they exhibited high activation rate constant and activated the alkyl bromide initiators five to six orders of magnitude faster than ht-PLPPAN.

Exploring Electrochemically Mediated ATRP of Styrene

Electrochemically mediated atom transfer radical polymerization (eATRP) of styrene was studied in detail by using CuBr2/TPMA (TPMA = tris(2-pyridylmethyl)amine) as a catalyst. Redox properties of various Cu(II) species were investigated in CH3CN, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) both in the absence and presence of 50% (v/v) styrene. This investigation together with preliminary eATRP experiments at 80 °C indicated DMF as the best solvent. The effects of catalyst, monomer, and initiator concentrations were also examined. The livingness of the polymerization was studied by chain extension and electrochemical temporal control of polymerization.

Catalytic Halogen Exchange in Supplementary Activator and Reducing Agent Atom Transfer Radical Polymerization for the Synthesis of Block Copolymers

Synthesis of block copolymers (BCPs) by catalytic halogen exchange (cHE) is reported, using supplemental activator and reducing agent Atom Transfer Radical Polymerization (SARA ATRP). The cHE mechanism is based on the use of a small amount of a copper catalyst in the presence of a suitable excess of halide ions, for the synthesis of block copolymers from macroinitiators with monomers of mismatching reactivity. cHE overcomes the problem of inefficient initiation in block copolymerizations in which the second monomer provides dormant species that are more reactive than the initiator. Model macroinitiators with low dispersity are prepared and extended to afford well-defined block copolymers of various compositions. Combined cHE/SARA ATRP is therefore a simple and potent polymerization tool for the copolymerization of a wide range of monomers allowing the production of tailored block copolymers.

Hierarchically Porous Carbon Materials from Self-Assembled Block Copolymer/Dopamine Mixtures

Hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores are desirable for electrochemical applications in biosensors, electrocatalysis, and supercapacitors. In this study, we report a facile synthetic route to fabricate hierarchically porous carbon materials by controlled macro- and mesophase separation of a mixture of polystyrene-block-poly(ethylene) and dopamine. The morphology of mesopores is tailored by controlling the coassembly of PS-b-PEO and dopamine in the acidic tetrahydrofuran-water cosolvent. HCl addition plays a critical role via enhancing the charge-dipole interactions between PEO and dopamine and suppressing the clustering and chemical reactions of dopamine in solution. As a result, subsequent drying can produce interpenetrated PS-b-PEO/DA mixtures without forming dopamine microsized crystallites. Dopamine oxidative polymerization induced by solvent annealing in NH₄OH vapor enables the formation of percolating macropores. Subsequent pyrolysis to selectively remove the PS-b-PEO template from the complex can produce hierarchically porous carbon materials with interconnected frameworks of macro- and mesopores when pyrolysis is implemented at a low temperature or when DA is a minor component.

Carbonization of single polyacrylonitrile chains in coordination nanospaces

It has been over half a century since polyacrylonitrile (PAN)-based carbon fibers were first developed. However, the mechanism of the carbonization reaction remains largely unknown. Structural evolution of PAN during the preoxidation reaction, a stabilization reaction, is one of the most complicated stages because many chemical reactions, including cyclization, dehydration, and cross-linking reactions, simultaneously take place. Here, we report the stabilization reaction of single PAN chains within the one-dimensional nanochannels of metal–organic frameworks (MOFs) to study an effect of interchain interactions on the stabilization process as well as the structure of the resulting ladder polymer (LP). The stabilization reaction of PAN within the MOFs could suppress the rapid generation of heat that initiates the self-catalyzed reaction and inevitably provokes many side-reactions and scission of PAN chains in the bulk state. Consequently, LP prepared within the MOFs had a more extended conjugated backbone than the bulk condition.

Accommodation of polyacrylonitrile in MOFs facilitated and regulated the transformation to ladder polymer in the carbonization process.

Surface-grafted polyacrylonitrile brushes with aggregation-induced emission properties

Polyacrylonitrile (PAN) brushes were grafted from silicon wafers by photoinduced ATRP and shown to exhibit aggregation-induced emission (AIE) properties.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Block copolymers for supercapacitors, dielectric capacitors and batteries

Block copolymer-based energy storage emerges as an active interdisciplinary research field. This topical review presents a survey of the recent advances in block copolymers for energy storage. In the first section, we introduce the background of electrochemical energy storage and block copolymer thermodynamics. In the second section, we discuss the current understandings of block copolymer chemistry, processing, pore size, and ionic conductivity. In the third section, we summarize the design principles and state-of-the-art applications of block copolymers in three energy storage devices, namely, supercapacitors, dielectric capacitors, and batteries. Lastly, we present our perspectives on future possible breakthroughs and associated challenges that are essential to propel the development of advanced block copolymers for energy storage. We expect the review to encourage innovative studies on integrating block copolymers into energy storage applications.

Polymer-Based Synthetic Routes to Carbon-Based Metal-Free Catalysts

Carbons are increasingly important as possible alternatives to expensive metal catalysts owing to the wide range of chemical properties they can exhibit and the growing set of synthetic routes available to produce them. This progress report discusses the process of making catalytic carbons from polymeric precursors, focusing on mechanisms of carbonization and how the polymer structures and synthetic procedures affect the resulting carbons. In considering what is necessary to move laboratory catalytic carbons to industrial and commercial applications, the cost and complexity to produce them are a considerable challenge to overcome. Industrially produced carbons are typically made from biopolymers such as lignin while many of the catalytic carbons studied in literature are from synthetic polymers. Thus, studying polymer-derived carbons can provide insights into the carbonization process and the properties of catalytic carbons, which can subsequently be translated to improve biopolymer-derived carbons in an economical way. Aspects of polymer carbonization discussed include carbonization mechanisms, effects of crosslinkers, polymer microstructure, heteroatom control, and effects of nanostructuring.

Soft-Templated Tellurium-Doped Mesoporous Carbon as a Pt-Free Electrocatalyst for High-Performance Dye-Sensitized Solar Cells

Among various photovoltaic devices, dye-sensitized solar cells (DSSCs) are one of the most potentially clean and renewable energy conversion devices because of their low fabrication cost, environmentally friendly nature, and high power conversion efficiency. However, the use of rare metals such as Pt counter electrodes (CEs) is one of the major drawbacks of DSSC devices for broad real-life applications. In this regard, alternative materials to Pt CEs have been long sought for DSSCs employing both cobalt and iodine redox couples. Therefore, in this study, soft-templated tellurium-doped mesoporous carbons (Te-SMCs) were synthesized for the first time by the simple pyrolysis of PAN- b-PBA block copolymer in the presence of a tellurium precursor for replacing the Pt CE. To confirm the chemical composition and porosity, the as-prepared Te-SMC materials were evaluated by elemental analysis (XPS and EDS) and nitrogen sorption isotherms measurement. The as-prepared Te-SMC materials contained mainly mesopores and retained the three-dimensional hierarchical graphite-like structure with many defect sites. They displayed doping levels with nitrogen of 9.15 atom % and tellurium of 0.15 atom % and had a specific surface area of 540 m² g^-1. Therefore, these characteristics enabled the development of a high-performance CE in DSSCs with cobalt and iodine redox couples. As a result of its catalytic performance, Te-SMC exhibited outstanding electrocatalytic activity as well as a significantly improved electrochemical stability than those of Pt CE for both redox couples even after 1000 potential cycles. The results show that a maximum conversion efficiency of 11.64 and 9.67% could be achieved under one sun illumination (AM 1.5G) for SGT-021/Co(bpy)₃^2+/3+- and N719/I^-/I₃^--based devices with Te-SMC CEs, and their power conversion efficiency is superior to the corresponding device with Pt CEs.