From Micropores to Ultra-micropores inside Hard Carbon: Toward Enhanced Capacity in Room-/ Low-Temperature Sodium-Ion Storage

Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries(SIBs).Ultra-micropores(<0.5 nm)of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na+but allow the entrance of naked Na^(+) into the pores,which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics.Herein,a molten diffusion-carbonization method is proposed to transform the micropores(>1 nm)inside carbon into ultra-micropores(<0.5 nm).Consequently,the designed carbon anode displays an enhanced capacity of 346 mAh g^(−1) at 30 mA g^(−1) with a high ICE value of~80.6%and most of the capacity(~90%)is below 1 V.Moreover,the high-loading electrode(~19 mg cm^(−2))exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm^(−2) at 25℃ and 5.32 mAh cm^(−2) at −20℃.Based on the in situ X-ray diffraction and ex situ solid-state nuclear magnetic resonance results,the designed ultra-micropores provide the extra Na+storage sites,which mainly contributes to the enhanced capacity.This proposed strategy shows a good potential for the development of high-performance SIBs.

Resorcinol-formaldehyde resin-based porous carbon spheres with high CO_2 capture capacities

Porous carbon spheres are prepared by direct carbonization of potassium salt of resorcinol-formaldehyde resin spheres, and are investigated as COadsorbents. It is found that the prepared carbon materials still maintain the typical spherical shapes after the activation, and have highly developed ultra-microporosity with uniform pore size, indicating that almost the activation takes place in the interior of the polymer spheres. The narrow-distributed ultra-micropores are attributed to the "in-situ homogeneous activation"effect produced by the mono-dispersed potassium ions as a form of -OK groups in the bulk of polymer spheres. The CS-1 sample prepared under a KOH/resins weight ratio of 1 shows a very high COcapture capacity of 4.83 mmol/g and good CO/Nselectivity of7-45. We believe that the presence of a welldeveloped ultra-microporosity is responsible for excellent COsorption performance at room temperature and ambient pressure.

Robust ultra-microporous metal-organic frameworks for highly efficient natural gas purification

The development of highly efficient separation technology for the purification of natural gas by removing ethane(C_(2)H_(6))and propane(C_(3)H_(8))is a crucial but challenging task to their efficient utilization in the chemical industry and social life.Here,we report three isomorphic ultra-microporous metal-organic frameworks(MOFs),M-pyz(M=Fe,Co,and Ni,and pyz=pyrazine)referred to as Fe-pyz,Co-pyz,and Ni-pyz,respectively,which possess high density of open metal sites and suitable pore structure.Compared with the benchmark materials reported,M-pyz not only has high adsorption capacities of C_(2)H_(6)and C_(3)H_(8)at low pressure(up to 51.6 and 63.7 cm^(3)·cm^(−3)),but also exhibits excellent C_(3)H_(8)/CH_(4)and C_(2)H_(6)/CH_(4)ideal adsorption solution theory(IAST)selectivities,111 and 25,respectively.Theoretical calculations demonstrated that the materials’separation performance was driven by multiple intermolecular interactions(hydrogen bonding interactions and van der Waals effect)between gas molecules(C_(2)H_(6)and C_(3)H_(8))and the M-pyz binding sites.And,dynamic breakthrough experiments verified the superior reusability and practical separation feasibility for the ternary CH_(4)/C_(2)H_(6)/C_(3)H_(8)mixtures.Furthermore,M-pyz can be synthesized rapidly and on a large scale at room temperature.This work presents a series of promising MOFs adsorbents to efficiently purify natural gas and promotes the industrial development process of MOFs materials.