Efficacy of hierarchical pore structure in enhancing the tribological and recyclable smart lubrication performance of porous polyimide

Herein,a porous oil-containing material with hierarchical pore structure was successfully prepared through microtexturing large pores on the surface of porous polyimide(PPI)with single-level small pores.Compared to the conventional oil-containing material,the hierarchically porous oil-containing material exhibited high oil-content,and retained excellent mechanical properties and high oil-retention because of the synergistic effects of large pores and small pores.Furthermore,the lubricant stored in the hierarchically porous polyimide could release to the interface under thermal-and-mechano-stimuli,and the released lubricant could be reabsorbed into the hierarchically porous polyimide via the capillary-force offered by the porous channel.Based on the high oil-content and recyclable oil release/reabsorption,the hierarchically porous oil-containing polyimide exhibited excellent lubrication performance(coefficient of friction was 0.057).Furthermore,the composite could perform 1,069 cycles of smart lubrication(1 h per cycle),which significantly extended the service life of the hierarchically porous oil-containing smart lubrication material.

Constructing a hollow core-shell structure of RuO_(2) wrapped by hierarchical porous carbon shell with Ru NPs loading for supercapacitor

Hollow core-shell structure nanomaterials have been broadly used in energy storage, catalysis, reactor,and other fields due to their unique characteristics, including the synergy between different materials,a large specific surface area, small density, large charge carrying capacity and so on. However, their synthesis processes were mostly complicated, and few researches reported one-step encapsulation of different valence states of precious metals in carbon-based materials. Hence, a novel hollow core-shell nanostructure electrode material, RuO_(2)@Ru/HCs, with a lower mass of ruthenium to reduce costs was constructed by one-step hydrothermal method with hard template and co-assembled strategy, consisting of RuO_(2) core and ruthenium nanoparticles(Ru NPs) in carbon shell. The Ru NPs were uniformly assembled in the carbon layer, which not only improved the electronic conductivity but also provided more active centers to enhance the pseudocapacitance. The RuO_(2) core further enhanced the material’s energy storage capacity. Excellent capacitance storage(318.5 F·g^(-1)at 0.5 A·g^(-1)), rate performance(64.4%) from 0.5 A·g^(-1)to 20 A·g^(-1), and cycling stability(92.3% retention after 5000 cycles) were obtained by adjusting Ru loading to 0.92%(mass). It could be attributed to the wider pore size distribution in the micropores which increased the transfer of electrons and protons. The symmetrical supercapacitor device based on RuO_(2)@Ru/HCs could successfully light up the LED lamp. Therefore, our work verified that interfacial modification of RuO_(2) and carbon could bring attractive insights into energy density for nextgeneration supercapacitors.

Facile assembly of mesoporous silica nanoparticles with hierarchical pore structure for CO2 capture

In the work,we propose an efficient one-pot approach for synthesis of a new type of mesoporous silica nanoparticles(MSNs).That can be successfully realized by using tetraethylorthosilicate(TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine(TSD) as the silica precursors and cetyltrimethylammonium bromide(CTAB) as the structure-directing agent through a facile assembly process.The as-synthesized MSNs possess a spherical morphology with about 230 nm,a relatively high surface area of133 m^2/g,and a hierarchical pore size distribution.When applied as the sorbents,the amine-functioned MSNs demonstrate the enhanced adsorption capacity for CO2 capture(at 1 bar,15 vol% CO2,up to80.5 mg/g at 75℃),high selectivity,and good cycling durability,benefiting from the suitable modification of polyethyleneimine.

Towards High-Energy and Anti-Self-Discharge Zn-Ion Hybrid Supercapacitors with New Understanding of the Electrochemistry

Aqueous Zn-ion hybrid supercapacitors(ZHSs)are increasingly being studied as a novel electrochemical energy storage system with prominent electrochemical performance,high safety and low cost.Herein,high-energy and anti-self-discharge ZHSs are realized based on the fibrous carbon cathodes with hierarchically porous surface and O/N heteroatom functional groups.Hierarchically porous surface of the fabricated free-standing fibrous carbon cathodes not only provides abundant active sites for divalent ion storage,but also optimizes ion transport kinetics.Consequently,the cathodes show a high gravimetric capacity of 156 mAh g^(−1),superior rate capability(79 mAh g^(−1)with a very short charge/discharge time of 14 s)and exceptional cycling stability.Meanwhile,hierarchical pore structure and suitable surface functional groups of the cathodes endow ZHSs with a high energy density of 127 Wh kg−1,a high power density of 15.3 kW kg^(−1)and good anti-self-discharge performance.Mechanism investigation reveals that ZHS electrochemistry involves cation adsorption/desorption and Zn_(4)SO_(4)(OH)_(6)·5H_(2)O formation/dissolution at low voltage and anion adsorption/desorption at high voltage on carbon cathodes.The roles of these reactions in energy storage of ZHSs are elucidated.This work not only paves a way for high-performance cathode materials of ZHSs,but also provides a deeper understanding of ZHS electrochemistry.

Shapeable carbon fiber networks with hierarchical porous structure for high-performance Zn–I;batteries

Aqueous rechargeable zinc-iodine batteries(ZIBs)emerging as a promising energy storage alternative have attracted considerable attention.However,ZIBs still suffer from the severe shuttle effect of polyiodide and poor reversibility,leading to the poor cycling lifetime and potential safety issues.Herein,the assembly of Al-based metal-organic frameworks(Al-MOFs)in the presence of polyacrylonitrile(PAN)via electrospinning technique enables the formation of Al-MOF/PAN fibers.With the subsequent pyrolysis,the hierarchical porous carbon fibers with nitrogen doping(NPCNFs)are prepared for loading iodine.Benefiting from the confinement effect of the highly porous carbon network and the nitrogen doping,the self-supported carbon nanofiber electrode is capable of inhibiting the shuttle effect of polyiodide species.Especially,the in-situ Raman spectroscopy reveals the reversible two-step conversion reaction between iodine and polyiodide,which enables the best cycling stability for over 6,000 cycles with negligible capacity.This work demonstrates an efficient approach to regulating the porous structure and surface properties in the design of advanced iodine electrodes for high-performance ZIBs.

Tofukasu-derived biochar with interconnected and hierarchical pores for high efficient removal of Cr (Ⅵ)

Herein,we report the synthesis of interconnected hierarchical pore biochar(HTB)via an ice-templating strategy using bio-waste(tofukasu).The abundance of N-and O-containing functional groups in tofukasu makes it easy to form hydrogen bonds with water molecules and water clusters,resulting in nano-micro structures like ice clusters and snow crystals during freezing process.More importantly,tofukasu will be squeezed by micron-scale snow crystals to form coiled sheet-like structures,and its surface and interior will be affected by needle-like ice nanocrystals from several nanometers to tens of nanometers to form transverse groove needles and mesopores.The ice crystals are then removed by sublimation with tofukasu,leaving the interconnected pore structure intact.Therefore,the ice template synthesis strategy endowed the interconnected hierarchical pore structure of HTB with a large specific surface area(SBET,733 m^(2)⋅g^(−1))and hierarchical porosity(30.30%for mesopores/total pore volume ratio),which is significantly higher than the normal dry treated tofukasu biochar(TB),which had a SBET of 436 m^(2)⋅g^(−1) and contained 1.53%mesopores.In addition,the sheet-like structure with interconnected pores of HTB favors high exposure of active sites(N-and O-containing functional groups),and a fast electron transport rate.As a result,HTB had an excellent adsorption capacity of 159.65 mg⋅g^(−1),which is 4.7 times that of typical block biochar of TB(33.89 mg⋅g^(−1))according to Langmuir model.Electrochemical characterization,FTIR and XPS analysis showed that the mechanism of Cr(Ⅵ)removal by HTB included electrostatic attraction,pore filling,reduction and surface complexation.

A Co-N/C hollow-sphere electrocatalyst derived from a metanilic CoAl layered double hydroxide for the oxygen reduction reaction, and its active sites in various pH media

Transition-metal-coordinating nitrogen-doped carbon catalysts （M-N/C, M = Co, Fe, Mn, Ni, etc.） are considered one of the most promising nonprecious-metal electrocatalysts for the oxygen reduction reaction （ORR）. However, they suffer from low ORR catalytic activity, and their active sites have not been fully identified. Herein, we report the synthesis of a porous Co-N/C hollow-sphere electrocatalyst by carbonization of metanilic anions between the layers of a Co-A1 layered double hydroxide. The as-prepared Co-N/C catalyst exhibited excellent ORR catalytic activity with a high half-wave potential and a large diffusion-limited current in alkaline and neutral solutions. The performance of the catalyst was comparable to those of commercial Pt/C electrocatalysts. Through investigating the effects of mask ions （SCN- and F-） on the ORR activity of the Co-N/C catalyst, and comparing the ORR activity before and after the destruction of Co-Nx sites in different pH media, we concluded that the Co-Nx sites act directly as the ORR active sites in acidic and neutral solutions, but have a negligible effect on the ORR activity in alkaline conditions.