Nitrogen-Enriched Hierarchically Porous Carbons Prepared from Polybenzoxazine for High-Performance Supercapacitors

Nitrogen-enriched hierarchically porous carbons (HPCs) were synthesized from a novel nitrile-functionalized benzoxazine based on benzoxazine chemistry using a soft-templating method and a potassium hydroxide (KOH) chemical activation method and used as electrode materials for supercapacitors. The textural and chemical properties could be easily tuned by adding a soft template and changing the activation temperature. The introduction of the soft-templating agent (surfactant F127) resulted in the formation of mesopores, which facilitated fast ionic diffusion and reduced the internal resistance. The micropores of HPCs were extensively developed by KOH activation to provide large electrochemical double-layer capacitance. As the activation temperature increased from 600 to 800 °C, the specific surface area of nitrogen-enriched carbons increased dramatically, micropores were enlarged, and more meso/macropores were developed, but the nitrogen and oxygen content decreased, which affected the electrochemical performance. The sample HPC-800 activated at 800 °C possesses a high specific surface area (1555.4 m² g^–1), high oxygen (10.61 wt %) and nitrogen (3.64 wt %) contents, a hierarchical pore structure, a high graphitization degree, and good electrical conductivity. It shows great pseudocapacitance and the largest specific capacitance of 641.6 F g^–1 at a current density of 1 A g^–1 in a 6 mol L^–1 KOH aqueous electrolyte when measured in a three-electrode system. Furthermore, the HPC-800 electrode exhibits excellent rate capability (443.0 F g^–1 remained at 40 A g^–1) and good cycling stability (94.3% capacitance retention over 5000 cycles)

Co₃O₄/MnO₂/Hierarchically Porous Carbon as Superior Bifunctional Electrodes for Liquid and All-Solid-State Rechargeable Zinc–Air Batteries

The design of efficient, durable, and affordable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very indispensable in liquid-type and flexible all-solid-state zinc–air batteries. Herein, we present a high-performance bifunctional catalyst with cobalt and manganese oxides supported on porous carbon (Co₃O₄/MnO₂/PQ-7). The optimized Co₃O₄/MnO₂/PQ-7 exhibited a comparable ORR performance with commercial Pt/C and a more superior OER performance than all of the other prepared catalysts, including commercial Pt/C. When applied to practical aqueous (6.0 M KOH) zinc–air batteries, the Co₃O₄/MnO₂/porous carbon hybrid catalysts exhibited exceptional performance, such as a maximum discharge peak power density as high as 257 mW cm^–2 and the most stable charge–discharge durability over 50 h with negligible deactivation to date. More importantly, a series of flexible all-solid-state zinc–air batteries can be fabricated by the Co₃O₄/MnO₂/porous carbon with a layer-by-layer method. The optimal catalyst (Co₃O₄/MnO₂/PQ-7) exhibited an excellent peak power density of 45 mW cm^–2. The discharge potentials almost remained unchanged for 6 h at 5 mA cm^–2 and possessed a long cycle life (2.5 h@5 mA cm^–2). These results make the optimized Co₃O₄/MnO₂/PQ-7 a promising cathode candidate for both liquid-type and flexible all-solid-state zinc–air batteries

Deep Catalytic Oxidative Desulfurization of Model Fuel Based on Modified Iron Porphyrins in Ionic Liquids: Anionic Ligand Effect

The modified iron porphyrins with weak ligand (PF₆^–, BF₄^–) were prepared by a gentle and cheap approach. The catalytic systems with modified iron porphyrins and 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]­PF₆) were used in the catalytic oxidative removal of sulfur compounds from model oil under mild conditions. The effect of anionic axial ligand on catalytic oxdative desulfurization performance was investigated. Iron porphyrins with weak ligand exhibited higher desulfurization performance, and the catalytic ability of catalysts was Fe^IIITPP­(PF₆) > Fe^IIITPP­(BF₄) > Fe^IIITPPCl. A dual active model mechanism was proposed to illustrate this phenomenon of oxidative process. The system of Fe^IIITPP­(PF₆) and [Bmim]­PF₆ could be recycled for 6 times without evident decrease of desulfurization efficiency

Sulfur-Doped Millimeter-Sized Microporous Activated Carbon Spheres Derived from Sulfonated Poly(styrene–divinylbenzene) for CO₂ Capture

Millimeter-sized activated carbon spheres are potential candidates for industrial-scale CO₂ capture. Millimeter-sized sulfur-doped microporous activated carbon spheres were synthesized from poly­(styrene–divinylbenzene), a very cheap and easily operated resin product, in the present work and studied for CO₂ uptake. A series of sulfur-doped spherical carbon materials were yielded through the sulfonation, oxidation, carbonization, and KOH activation of the polymer precursors. In addition to promoting the cross-linking of the polymer molecules, the sulfonic substituents directly introduced sulfur functional groups into the carbon materials after pyrolysis. The SCS-700 sample showed the best CO₂ adsorption performance, whose sulfur content reached 0.69 wt %, and exhibited a high surface area of 1526 m² g^–1 and a large pore volume of 0.726 cm³ g^–1. The adsorbent showed high CO₂ uptake at both 25 °C (4.21 mmol g^–1) and 50 °C (2.54 mmol g^–1) under ambient pressure due to its abundant ultramicropores and a high proportion of oxidized sulfur functional groups. Thanks to its high microporous volume of 0.617 cm³ g^–1, the CO₂ performance at 8 bar was 10.66 mmol g^–1 at 25 °C. The thermodynamics indicated the exothermic and spontaneous nature of the adsorption process, which was dominated by a physisorption mechanism. Furthermore, the CO₂ uptake curves on a TGA analyzer were fitted with different kinetic models, and the fractional order model showed the best agreement with the experimental data. The recycling curve of SCS-700 exhibited excellent cyclic adsorption performance with no significant capacity loss even after ten adsorption–desorption cycles. It is suggested that this excellent CO₂ uptake was due to the synergistic effect of the well-developed microporous structure and the oxidized sulfur-containing functional groups

Disproportionation in Li–O₂ Batteries Based on a Large Surface Area Carbon Cathode

In this paper we report on a kinetics study of the discharge process and its relationship to the charge overpotential in a Li–O₂ cell for large surface area cathode material. The kinetics study reveals evidence for a first-order disproportionation reaction during discharge from an oxygen-rich Li₂O₂ component with superoxide-like character to a Li₂O₂ component. The oxygen-rich superoxide-like component has a much smaller potential during charge (3.2–3.5 V) than the Li₂O₂ component (∼4.2 V). The formation of the superoxide-like component is likely due to the porosity of the activated carbon used in the Li–O₂ cell cathode that provides a good environment for growth during discharge. The discharge product containing these two components is characterized by toroids, which are assemblies of nanoparticles. The morphologic growth and decomposition process of the toroids during the reversible discharge/charge process was observed by scanning electron microscopy and is consistent with the presence of the two components in the discharge product. The results of this study provide new insight into how growth conditions control the nature of discharge product, which can be used to achieve improved performance in Li–O₂ cell