Bimodal Mesoporous Carbon Spheres with Small and Ultra-Large Pores Fabricated Using Amphiphilic Brush Block Copolymer Micelle Templates

Mesoporous Single Atom-Cluster Fe-N/C Oxygen Evolution Electrocatalysts Synthesized with Bottlebrush Block Copolymer-Templated Rapid Thermal Annealing

Current electrocatalysts for oxygen evolution reaction (OER) are either expensive (such as IrO2, RuO2) or/and exhibit high overpotential as well as sluggish kinetics. This article reports mesoporous earth-abundant iron (Fe)-nitrogen (N) doped carbon electrocatalysts with iron clusters and closely surrounding Fe-N4 active sites. Unique to this work is that the mechanically stable mesoporous carbon-matrix structure (79 nm in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster is synthesized via rapid thermal annealing (RTA) within only minutes using a self-assembled bottlebrush block copolymer (BBCP) melamine-formaldehyde resin composite template. The resulting porous structure and domain size can be tuned with the degree of polymerization of the BBCP backbone, which increases the electrochemically active surface area and improves electron transfer and mass transport for an effective OER process. The optimized electrocatalyst shows a required potential of 1.48 V (versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade at a given overpotential of 250 mV, which is significantly lower than recently reported earth-abundant electrocatalysts. Importantly, the Fe single-atom nitrogen coordination environment facilitates the surface reconstruction into a highly active oxyhydroxide under OER conditions, as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms reactive sites to prevent demetalation during the OER process. Density functional theory (DFT) calculations support that the iron nitrogen environment and reconstructed oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced. This work has opened a new avenue for simple, rapid synthesis of inexpensive, earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated single-atom electrocatalysts that can be used for renewable energy production.

Tunable Hierarchically Structured Meso-Macroporous Carbon Spheres from a Solvent-Mediated Polymerization-Induced Self-Assembly

Herein, we report a versatile solvent-mediated polymerization-induced self-assembly (PISA) strategy to directly synthesize highly N-doped hierarchically porous structured carbon spheres with a tunable meso-macroporous configuration. The introduction of intermolecular hydrogen bonds is verified to enhance the interfacial interactions between block copolymers, oil droplets, and polyphenols. Moreover, the dominant hydrogen-bond-driven interactions can be systematically manipulated by selecting different cosolvent systems to generate diverse porous structures from the transformation of micellar and precursor co-assembly. Impressively, hierarchically structured meso-macroporous N-doped carbon spheres present simultaneously tunable sphere sizes and mesopores and macropores, ranging from 1.2 μm, 9/50 and 227 nm to 1.0 μm, 40, and 183 nm and 480, 24, and 95 nm. As a demonstration, dendritic-like N-doped hierarchically meso-macroporous carbon spheres manifest excellent enzyme-like activity, which is attributed to the continuous mass transport from the multiordered porosity. The current study provides a new platform for the synthesis of novel well-defined porous materials.

Porous Carbon Nanofiber Flexible Membranes via a Bottlebrush Copolymer Template for Enhanced High-Performance Supercapacitors

We report a method to construct ordered hierarchical porous structures in carbon nanofiber membranes using poly(ethylene oxide)-block-polydimethylsiloxane bottlebrush block copolymers (BBCPs) as templates. The BBCPs self-assemble into a spherical morphology driven by small-molecule hydrogen bond donors which act as bridges between carbon precursors and templates to promote uniform dispersion of the templates. We successfully obtained flexible, self-supporting, and porous carbon nanofiber membranes (PCNFs) with high porosity. Then, a supercapacitor electrode was independently prepared using PCNFs as an active substance without infiltrating any conductive agents or binders. The PCNFs exhibit excellent performance with a capacitance of 234.1 F g^-1 at a current density of 1 A g^-1 owing to the abundant hierarchical porous structures and high content of nitrogen and oxygen elements internally. The aqueous symmetric supercapacitor prepared using PCNFs electrodes maintains more than 95% capacitance retention after 55,000 charge-discharge cycles. Furthermore, the capacitance retention reaches up to 67.72% at a current density of 50 A g^-1 (compared to 1 A g^-1), exhibiting excellent cycling stability and rate capability. Based on the excellent electrochemical performance and flexible self-supporting ability of PCNFs, this work is expected to facilitate the development of flexible displays, flexible sensors, wearable devices, and electrocatalysis.

NIR light-propelled bullet-shaped carbon hollow nanomotors with controllable shell thickness for the enhanced dye removal

Materials with asymmetric nanostructures have attracted tremendous research attention due to their unique structural characteristics, excellent physicochemical properties, and promising prospects. However, it is still difficult to design and fabricate bullet-shaped nanostructure due to its structural complexity. Herein, for the first time, we successfully constructed NIR light-propelled bullet-shaped hollow carbon nanomotors (BHCNs) with an open mouth on the bottom of nano-bullet for the enhanced dye removal, by employing bullet-shaped silica nanoparticles (B-SiO₂ NPs) as a hard template. BHCNs were formed by the growth of polydopamine (PDA) layer on the heterogeneous surface of B-SiO₂ NPs, followed by the carbonization of PDA and subsequent selective etching of SiO₂. The shell thickness of BHCNs was able to be facilely controlled from ≈ 14 to 30 nm by tuning the added amount of dopamine. The combination of streamlined bullet-shaped nanostructure with good photothermal conversion efficiency of carbon materials facilitated the generation of asymmetric thermal gradient field around itself, thus driving the motion of BHCNs by self-thermophoresis. Noteworthily, the diffusion coefficient (De) and velocity of BCHNs with shell thickness of 15 nm (BHCNs-15) reached to 43.8 μm⋅cm^-2 and 11.4 μm⋅s^-1, respectively, under the illumination of 808 nm NIR laser with the power density of 1.5 W⋅cm^-2. The NIR laser propulsion caused BCHNs-15 to enhance the removal efficiency (53.4% vs. 25.4%) of methylene blue (MB) as a typical dye because the faster velocity could produce the higher micromixing role between carbon adsorbent and MB. Such a smart design of the streamlined nanomotors may provide a promising potential in environmental treatment, biomedical and biosensing applications.

Mechanically Strong and Electrically Conductive Polyethylene Oxide/Few-Layer Graphene/Cellulose Nanofibrils Nanocomposite Films

In this work, a cellulose nanofibrils (CNFs)/few-layer graphene (FLG) hybrid is mechanically stripped from bamboo pulp and expanded graphene (EG) using a grinder. This strategy is scalable and environmentally friendly for high-efficiency exfoliation and dispersion of graphene in an aqueous medium. The in situ-generated CNFs play a key role in this process, acting as a "green" dispersant. Next, the obtained CNFs-FLG is used as a functional filler in a polyoxyethylene (PEO) matrix. When the composition of CNFs-FLG is 50 wt.%, the resultant PEO/CNFs-FLG nanocomposite film exhibits a Young's modulus of 1.8 GPa and a tensile strength of 25.7 MPa, showing 480% and 260% enhancement as compared to those of the pure PEO film, respectively. Remarkably, the incorporation of CNFs-FLG also provides the nanocomposite films with a stunning electrical conductivity (72.6 S/m). These attractive features make PEO/CNFs-FLG nanocomposite films a promising candidate for future electronic devices.

Upgrading Waste Activated Carbon by Equipping Micro-/Mesopore-Dominant Microstructures from the Perspective of Circular Economy

Equipping wastes with interesting properties in response to the circular economy could release environmental burdens by reducing resource exploitation and material manufacturing. In this study, we demonstrated that the waste regenerated activated carbon (RAC) could become micro-/mesopore-dominant through a simple surfactant/gel modification. This was achieved by associating carbon precursors, such as commercially available low-cost surfactants/methyl cellulose thickening reagents, with the pores of RAC. Following heat treatment, associated carbon precursors were carbonized, hence modifying the microstructure of RAC to be micro-/mesopore-dominant. The surfactant modification gave rise to a micropore-dominant RAC by increasing the micropore volume (PVmicro) together with significantly decreasing the mesopore volume (PVmeso) and macropore volume (PVmacro). In contrast, gel modification led to mesopore-rich RAC by blocking micropores with carbonized methyl cellulose and a surfactant matrix. Interestingly, both surfactant/gel modifications were insensitive to the properties of the surfactant applied, which provided a new alternative for waste/low-grade surfactant mixture disposal. Our results provide an important demonstration that waste could be effectively upgraded with a rational design by exhibiting new properties in response to the circular economy.

Nanoengineering of N-doped Mesoporous Carbon Nanoparticles with Adjustable Internal Cavities via Emulsion-Induced Assembly

The preparation of mesoporous carbonaceous materials with particularly adjustable morphology is currently a hot area of research in mesoporous materials. Herein, a novel approach is reported for the construction of N-doped multicavity mesoporous carbon nanoparticles (NMMCNs) based on the “emulsion swelling–acid curing mechanism” using a nanoemulsion assembly method under a high-speed shearing force. Intriguingly, this approach adopted a novel acid (HCl) curing procedure. Impressively, the morphology evolution from an internal multicavity to a single cavity and then to a non-cavity interior structure could be accomplished by simply varying the synthesis parameters. Additionally, this synthesis approach ingeniously overcame the following problems: (i) technically, the employment of high temperatures and high pressures in traditional hydrothermal reaction curing environments is avoided; (ii) this approach removes the requirement for silicon coating, which provides a limited pyrolysis condition, to obtain a multi-chamber structure. Resveratrol (Res) is an insoluble natural medicine and was successfully loaded into NMMCNs, thereby the Res–NMMCNs delivery system was constructed. Importantly, the Res–NMMCNs delivery system could still retain the antitumor and antioxidant activity of Res in vitro.

Challenges and Strategies towards Practically Feasible Solid-State Lithium Metal Batteries

Remarkable improvement of the ionic conductivity of inorganic solid electrolytes (SEs) exceeding 10 mS cm^-1 at room temperature has opened up the opportunities to realize the commercialization of solid-state batteries (SSBs). The transition to the intrinsically inflammable SEs also promises that SSBs would successfully utilize lithium metal anode thus achieving the high-energy-density lithium metal batteries without the risk of a safety hazard. However, the practical operation of solid-state lithium metal batteries (SSLMBs) still faces the challenges of the poor cycle stability and the low energy efficiency, which are coupled with the interface stability and even with the dendrite growth of lithium metal. This article overviews current understandings regarding the underlying origins of the issues in employing the lithium metal anode in SSLMBs from the five main standpoints: i) the chemical/electrochemical interfacial stability, ii) the microscopic evolution of interfacial morphology, iii) the intrinsic diffusivity of lithium atom/vacancy at the interface, iv) imperfections (defect/pores), and v) non-negligible electronic conductivity of SEs. The discussions are followed on the state-of-the-art efforts and strategies to overcome these respective challenges. Finally, the authors provide their perspectives for the future research directions toward achieving the commercial level of high-energy SSLMBs.