Effect of ultramicropores and inner space of carbon materials on the capacitive sodium storage performance

1.Introduction Carbon materials have been widely investigated as the anode materials for Na+storage due to their moderate capacity,good stability,and low cost.The Na+storage mechanisms of carbon are generally classified into diffusion-controlled interlayer insertion/desertion and capacitive-controlled surface adsorption/desorption[1].

Size Determination of Ultramicropores and Small Mesopores Using a Calculation Procedure Based on the Tangents of Comparison Plot

Pore size distribution（PSD） curves of synthesized hollow silica spheres with ultrmicropores and small mesopores were obtained from calculations based on the BJH,KJS,SF,MP,NLDFT models and Prof.Zhu＇s method.Comparisons indicate that Zhu＇s method not only gives reasonable small mesopore size but also could be further extended to the ultramicropores region for the PSD evaluation.

A novel one-step reaction sodium-sulfur battery with high areal sulfur loading on hierarchical porous carbon fiber

Room temperature sodium-sulfur(RT Na-S)batteries are gaining extensive attention as attractive alternatives for large-scale energy storage,due to low cost and high abundancy of sodium and sulfur in nature.However,the dilemmas regarding soluble polysulfides(Na_(2)Sn,4<n<8)and the inferior reaction kinetics limit their practical application.To address these issues,we report the activated porous carbon fibers(APCF)with small sulfur molecules(S2-4)confined in ultramicropores,to achieve a reversible single-step reaction in RT Na-S batteries.The mechanism is investigated by the in situ UV/vis spectroscopy,which demonstrates Na2S is the only product during the whole discharge process.Moreover,the hierarchical carbon structure can enhance areal sulfur loading without sacrificing the capacity due to thorough contact between electrolyte and sulfur electrode.As a consequence,the APCF electrode with 38 wt%sulfur(APCF-38S)delivers a high initial reversible specific capacity of 1412 mAh g^(-1) and 10.6mAh cm^(-2)(avg.areal sulfur loading:7.5 mg cm^(-2))at 0.1 C(1C=1675 mA g^(-1)),revealing high degree of sulfur utilization.This study provides a new strategy for the development of high areal capacity RT Na-S batteries.

Perspective on ultramicroporous carbon as sulphur host for Li-S batteries

Lithium-sulphur(Li-S)batteries are currently considered as next-generation battery technology.Sulphur is an attractive positive electrode for lithium metal batteries,mainly due to its high capacity(1675 m Ah g^(-1))and high specific energy(2600 Wh kg^(-1)).The electrochemical reaction of lithium with sulphur in non-aqueous electrolytes results in the formation of electrolyte soluble intermediate lithium-polysulphides.The dissolved polysulphides shuttle to the anode and get reduced at the anode resulting in Li metal corrosion.The solubility of polysulphide gradually reduces the amount of sulphur in the cathode,thereby limiting the cycle life of Li-S batteries.Several strategies have been proposed to improve the cycling stability of Li-S batteries.A unique approach to eliminate the polysulphide shuttle is to use ultramicroporous carbon(UMC)as a host for sulphur.The pore size of UMC which is below 7A,is the bottleneck for carbonate solvents to access sulphur/polysulphides confined in the pores,thereby preventing the polysulphide dissolution.This perspective article will emphasise the role of UMC host in directing the lithiation mechanism of sulphur and in inhibiting polysulphide dissolution,including the resulting parasitic reaction on the lithium anode.Further,the challenges that need to be addressed by UMC-S based Li-S batteries,and the strategies to realise high power density,high Coulombic efficiency,and resilient Li-S batteries will be discussed.

Efficient Splitting of Trans-/Cis-Olefins Using an Anion-Pillared Ultramicroporous Metal-Organic Framework with Guest-Adaptive Pore Channels

Trans-/cis-olefin isomers play a vital role in the petrochemical industry.The paucity of energy-efficient technologies for their splitting is mainly due to the similarities of their physicochemical properties.Herein,two new tailor-made anion-pillared ultramicroporous metal–organic frameworks(MOFs),ZU-36-Ni and ZU-36-Fe(GeFSIX-3-Ni and GeFSIX-3-Fe)are reported for the first time for the efficient trans-/cis-2-butene(trans-/cis-C_(4)H_(8))mixture splitting by enhanced molecular exclusion.Notably,ZU-36-Ni unexpectedly exhibited smart guest-adaptive pore channels for trapping trans-C_(4)H_(8)with a remarkable adsorption capacity(2.45 mmol∙g^(−1))while effectively rejecting cis-C_(4)H_(8)with a high purity of 99.99%.The dispersion-corrected density functional theory(DFT-D)calculation suggested that the guest-adaptive behavior of ZU-36-Ni in response to trans-C_(4)H_(8)is derived from the organic linker rotation and the optimal pore dimensions,which not only improve the favorable adsorption/diffusion of trans-C_(4)H_(8)with optimal host–guest interactions,but also enhance the size-exclusion of cis-C_(4)H_(8).This work opens a new avenue for pore engineering in advanced smart or adaptive porous materials for specific applications involving guest molecular recognition.

A thiophene-containing covalent triazine-based framework with ultramicropore for CO2 capture

In this work, a 2D covalent triazine-based framework was prepared by using 1,3-dicyanobenzo[c]thiophene（DCBT） as monomer to effectively capture CO. The resulting CTF-DCBT was characterized by FT-IR, XPS, PXRD, elemental analysis, SEM, TEM, and Nadsorption-desorption.The results indicate that CTF-DCBT is partially crystalline and has ultramicropore（6.5 A?） as well as high heteroatom contents（11.24 wt% and 12.61 wt% for N and S, respectively）. In addition, the BET surface area and total pore volume of CTF-DCBT are 500 m/g and 0.26 cm/g, respectively. CTF-DCBT possesses excellent thermal stability（450 °C） and chemical stability towards boiling water, 4 M HCl, and 1 M Na OH.The COadsorption capacity of CTF-DCBT is 37.8 cm/g at 1 bar and 25 °C. After six adsorption-desorption cycles, there is no obvious loss of COuptake observed. Due to the ultramicropore and high heteroatom contents, CTF-DCBT has high isosteric heats of adsorption for COand high selectivities of COover Nand CH. At 25 °C, the CO/Nand CO/CHselectivities are 112.5 and 10.3, respectively, which are higher than those of most POFs. Breakthrough curves indicate that CTF-DCBT could effectively separate CO/Nand CO/CHmixtures.

Highly N/O co-doped ultramicroporous carbons derived from nonporous metal-organic framework for high performance supercapacitors

A new nonporous Zn-based metal-organic framework(NPMOF) synthesized from a high nitrogencontaining rigid ligand was converted into porous carbon materials by direct carbonization without adding additional carbon sources.A series of NPMOF-derived porous carbons with very high N/O contents(24.1% for NPMOF-700,20.2% for NPMOF-800,15.1% for NPMOF-900) were prepared by adjusting the pyrolysis temperatures.The NPMOF-800 fabrica ted electrode exhibits a high capacitance of220 F/g and extremely large surface area normalized capacitance of 57.7 μF/cm~2 compared to other reported MOF-derived porous carbon electrodes,which could be attributed to the abundant ultramicroporosity and high N/O co-doping.More importantly,symmetric supercapacitor assembled with the MOF-derived carbon manifests prominent stability,i.e.,99.1 % capacitance retention after 10,000 cycles at 1.0 A/g.This simple preparation of MOF-derived porous carbon materials not only finds an application direction for a variety of porous or even nonporous MOFs,but also opens a way for the production of porous carbon materials for superior energy storage.

Synthesis of MnO2/N-doped ultramicroporous carbon nanospheres for high-performance supercapacitor electrodes

We demonstrate a simple and highly efficient strategy to synthesize MnO2/nitrogen-doped ultramicroporous carbon nanospheres（MnO2/N-UCNs） for supercapacitor application.MnO2/N-UCNs were fabricated via a template-free polymerization of resorcinol/formaldehyde on the surface of phloroglucinol/terephthalaldehyde colloids in the presence of hexamethylenetetramine,followed by carbonization and then a redox reaction between carbons and KMnO4.As-prepared MnO2/N-UCNs exhibits regular ultramicropores,high surface area,nitrogen heteroatom,and high content of MnO2.A typical MnO2/N-UCNs with 57 wt.%MnO2 doping content（denoted as MnO2（57%）/N-UCNs） makes the most use of the synergistic effect between carbons and metal oxides.MnO2（57%）/N-UCNs as a supercapacitor electrode exhibits excellent electrochemical performance such as a high specific capacitance（401 F/g at 1.0 A/g） and excellent charge/discharge stability（86.3%of the initial capacitance after 10,000 cycles at 2.0 A/g） in 1.0 mol/L Na2SO4 electrolyte.The well-designed and high-performance MnO2/N-UCNs highlight the great potential for advanced supercapacitor applications.