Large-Area Fabrication of Porous Graphene Networks on Carbon Fabric via Millisecond Photothermal Processing of Polyaniline for Supercapacitors.

Supercapacitors demonstrate promising potential for flexible, multi-functional energy storage devices; however, their widespread adoption is confronted by fabrication challenges. To access a combination of desirable device qualities such as flexibility, lightweight, structural stability, and enhanced electrochemical performance, carbon fiber (CF) can be utilized as a current collector, alongside graphene as an electrochemically active material. Yet achieving a cost-effective, large-scale graphene production, particularly on CF, remains challenging. Here, a rapid (<1 min) photothermal approach is developed for the large-scale production of graphene directly onto CF, utilizing polyaniline (PANI) as a polymer precursor. The in situ electropolymerization of PANI on CF facilitates its rapid synthesis on large areas, followed by conversion into graphene networks, enabling the binder-free fabrication of supercapacitor devices. These devices exhibit an areal capacitance of 180 mF cm-2 (at 2 mA cm-2 in 1 m H2SO4), an order of magnitude higher than other fabric-based devices. Moreover, the devised photothermal strategy allows for one-step preparation of supercapacitor devices on areas exceeding 100 cm-2, yielding an absolute areal capacitance of 4.5 F. The proportional increase in capacitance with device area facilitates scaling and indicates the commercial viability of this approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based multi-functional supercapacitor devices.

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.

Defect Healing in Graphene via Rapid Thermal Annealing with Polymeric "Nanobandage".

Overcoming throughput challenges in current graphene defect healing processes, such as conventional thermal annealing, is crucial for realizing post-silicon device fabrication. Herein, a new time- and energy-efficient method for defect healing in graphene is reported, utilizing polymer-assisted rapid thermal annealing (RTA). In this method, a nitrogen-rich, polymeric "nanobandage" is coated directly onto graphene and processed via RTA at 800 °C for 15 s. During this process, the polymer matrix is cleanly degraded, while nitrogen released from the nanobandage can diffuse into graphene, forming nitrogen-doped healed graphene. To study the influence of pre-existing defects on graphene healing, lattice defects are purposefully introduced via electron beam irradiation and investigated by Raman microscopy. X-ray photoelectron spectroscopy reveals successful healing of graphene, observing a maximum doping level of 3 atomic nitrogen % in nanobandage-treated samples from a baseline of 0-1 atomic % in non-nanobandage treated samples. Electrical transport measurements further indicate that the nanobandage treatment recovers the conductivity of scanning electron microscope-treated defective graphene at ≈85%. The reported polymer-assisted RTA defect healing method shows promise for healing other 2D materials with other dopants by simply changing the chemistry of the polymeric nanobandage.

Mesoscale Polymer Surfactants: Photolithographic Production and Localization at Droplet Interfaces.

Stabilization of fluid droplets, classically as oil-in-water or water-in-oil emulsions, is typically conducted using molecular surfactants or small particulates that localize at oil-water interfaces. In this paper, we describe a method whereby thin polymer films are converted photolithographically to ribbon-like mesoscale objects, which, in turn, adsorb to fluid interfaces where they extend as appendages, or arms, from the droplet surface. These "mesoscale polymer surfactants", or MPSs, were prepared from thin polymer films containing reactive functional moieties, including coumarin for photo-cross-linking, triphenylsulfonium for photoacid generation, and tert-butyl ester for solubility switching. The resultant MPSs, prepared initially on Si substrates, were released into water to reveal an exquisite shape sensitivity (forming straight, bent, or helical structures) and affinity for droplet interfaces based on their preparation conditions and the properties of the surrounding liquid. Notably, the lithographic techniques employed were amenable to differentiating the wettability of MPS segments, affording access to diblock-like MPSs which adhered to dispersed droplets via their hydrophobic segments, allowing their hydrophilic segments to extend into the continuous phase.

Stabilization of Three-Particle Excitations in Monolayer MoS2 by Fluorinated Methacrylate Polymers.

While extrinsic factors, such as substrates and chemical doping, are known to strongly influence visible photoemission from monolayer MoS2, key fundamental knowledge for p-type polymeric dopants is lacking. We investigated perturbations to the electronic environment of 2D MoS2 using fluorinated polymer coatings and specifically studied stabilization of three-particle states by monitoring changes in intensities and emission maxima of three-particle and two-particle emissions. We calculated changes in carrier density and trion binding energy, the latter having an additional contribution from MoS2 polarization by the polymer. Polarization is further suggested by Kelvin probe force microscopy (KPFM) measurements of large Fermi level shifts. Changes similar in magnitude, but opposite in sign, were observed in 2D MoS2 coated with an analogous nonfluorinated polymer. These findings highlight the important interplay between electron exchange and electrostatic interactions at the interface between polymers and transition metal dichalcogenides (TMDCs), which govern fundamental electronic properties relevant to next-generation devices.

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors.

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V2O5 without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V2O5 deposition yielded pseudocapacitors with 10-fold increase in energy density (20 µW h cm-2 µm-1) without adversely affecting the high power density (450 µW cm-2 µm-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.

Polarization-Driven Asymmetric Electronic Response of Monolayer Graphene to Polymer Zwitterions Probed from Both Sides.

We investigated the nature of graphene surface doping by zwitterionic polymers and the implications of weak in-plane and strong through-plane screening using a novel sample geometry that allows direct access to either the graphene or the polymer side of a graphene/polymer interface. Using both Kelvin probe and electrostatic force microscopies, we observed a significant upshift in the Fermi level in graphene of ∼260 meV that was dominated by a change in polarizability rather than pure charge transfer with the organic overlayer. This physical picture is supported by density functional theory (DFT) calculations, which describe a redistribution of charge in graphene in response to the dipoles of the adsorbed zwitterionic moieties, analogous to a local DC Stark effect. Strong metallic-like screening of the adsorbed dipoles was observed by employing an inverted geometry, an effect identified by DFT to arise from a strongly asymmetric redistribution of charge confined to the side of graphene proximal to the zwitterion dipoles. Transport measurements confirm n-type doping with no significant impact on carrier mobility, thus demonstrating a route to desirable electronic properties in devices that combine graphene with lithographically patterned polymers.

Electronic Tuning of Monolayer Graphene with Polymeric "Zwitterists".

Work function engineering of two-dimensional (2D) materials by application of polymer coatings represents a research thrust that promises to enhance the performance of electronic devices. While polymer zwitterions have been demonstrated to significantly modify the work function of both metal electrodes and 2D materials due to their dipole-rich structure, the impact of zwitterion chemical structure on work function modulation is not well understood. To address this knowledge gap, we synthesized a series of sulfobetaine-based zwitterionic random copolymers with variable substituents and used them in lithographic patterning for the preparation of negative-tone resists (i.e., "zwitterists") on monolayer graphene. Ultraviolet photoelectron spectroscopy indicated a significant work function reduction, as high as 1.5 eV, induced by all polymer zwitterions when applied as ultrathin films (<10 nm) on monolayer graphene. Of the polymers studied, the piperidinyl-substituted version, produced the largest dipole normal to the graphene sheet, thereby inducing the maximum work function reduction. Density functional theory calculations probed the influence of zwitterion composition on dipole orientation, while lithographic patterning allowed for evaluation of surface potential contrast via Kelvin probe force microscopy. Overall, this polymer "zwitterist" design holds promise for fine-tuning 2D materials electronics with spatial control based on the chemistry of the polymer coating and the dimensions of the lithographic patterning.