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

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.

Dielectric constant enhancement of poly 4-vinylphenol (PVPh) via graphene flakes incorporation through electrospray atomization for energy storage

We report on the fabrication of hybrid composite poly 4-vinlyphenol (PVPh)/graphene thin film via cost-effective electrospray atomization deposition technique. Thin films fabricated through manipulating deposition technique in two different ways which are blending and layer by layer (LBL). For investigation of PVPh/graphene hybrid composite dielectric behavior in comparison to PVPh; three asymmetric MIS thin film capacitors were fabricated, where dielectric thin films (i) PVPh and (ii & iii) hybrid composite thin films PVPh/graphene (blended and LBL) were sandwiched between electrodes i.e. indium tin oxide (ITO) and p-type semiconductor poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The dielectric properties of the thin films were characterized for frequencies 1 to 100 kHz while utilizing the MIS thin film capacitors. The capacitance obtained at 1 kHz frequency for PVPh/graphene (LBL) dielectric layer at the voltage range ±10 volts was 8.5 mF cm-2 while for blended PVPh/graphene thin film the capacitance at the voltage range ±3 volts was 0.40 μF cm-2 and for pristine PVPh as dielectric layer the capacitance at voltage range ±1 volts was 1.45 μF cm-2. Similarly, even at higher frequencies up to 100 kHz, the PVPh/graphene (LBL) showed stable behavior. Thus, the composite PVPh/graphene (LBL) thin film has a better dielectric nature compared to the composite PVPh/graphene (blended) thin film, even at higher frequencies with larger operational voltage window. This distinguishing nature of the composite PVP/graphene (LBL) is attributed to increase in dielectric constant due to graphene flakes in between PVPh. For the thin films LBL and blended PVPh/graphene, the calculated dielectric constant at 10 kHz is 6.7 and 0.023 while at 100 kHz it is 2 and 0.0167, respectively.

Al Foil-Supported Carbon Nanosheets as Self-Supporting Electrodes for High Areal Capacitance Supercapacitors

Self-supporting electrode materials with the advantages of a simple operation process and the avoidance of the use any binders are promising candidates for supercapacitors. In this work, carbon-based self-supporting electrode materials with nanosheets grown on Al foil were prepared by combining hydrothermal reaction and the one-step chemical vapor deposition method. The effect of the concentration of the reaction solution on the structures as well as the electrochemical performance of the prepared samples were studied. With the increase in concentration, the nanosheets of the samples became dense and compact. The CNS-120 obtained from a 120 mmol zinc nitrate aqueous solution exhibited excellent electrochemical performance. The CNS-120 displayed the highest areal capacitance of 6.82 mF cm-2 at the current density of 0.01 mA cm-2. Moreover, the CNS-120 exhibited outstanding rate performance with an areal capacitance of 3.07 mF cm-2 at 2 mA cm-2 and good cyclic stability with a capacitance retention of 96.35% after 5000 cycles. Besides, the CNS-120 possessed an energy density of 5.9 μWh cm-2 at a power density of 25 μW cm-2 and still achieved 0.3 μWh cm-2 at 4204 μW cm-2. This work provides simple methods to prepared carbon-based self-supporting materials with low-cost Al foil and demonstrates their potential for realistic application of supercapacitors.

Direct synthesis of ordered mesoporous materials from thermoplastic elastomers

The ability to manufacture ordered mesoporous materials using low-cost precursors and scalable processes is essential for unlocking their enormous potential to enable advancement in nanotechnology. While templating-based methods play a central role in the development of mesoporous materials, several limitations exist in conventional system design, including cost, volatile solvent consumption, and attainable pore sizes from commercial templating agents. This work pioneers a new manufacturing platform for producing ordered mesoporous materials through direct pyrolysis of crosslinked thermoplastic elastomer-based block copolymers. Specifically, olefinic majority phases are selectively crosslinked through sulfonation reactions and subsequently converted to carbon, while the minority block can be decomposed to form ordered mesopores. We demonstrate that this process can be extended to different polymer precursors for synthesizing mesoporous polymer, carbon, and silica. Furthermore, the obtained carbons possess large mesopores, sulfur-doped carbon framework, with tailorable pore textures upon varying the precursor identities.