Three-dimensional ordered hierarchically porous carbon materials for high performance Li-Se battery

Developing host materials with high specific surface area, good electron conductivity, and fast ion transportation channel is critical for high performance lithium-selenium(Li-Se) batteries. Herein, a series of three dimensional ordered hierarchically porous carbon(3D OHPC) materials with micro/meso/macropores are designed and synthesized for Li-Se battery. The porous structure is tuned by following the concept of the generalized Murray’s law to facilitate the mass diffusion and reduce ion transport resistance.The optimized 3D Se/OHPC cathode exhibits a very high 2 nd discharge capacity of 651 m Ah/g and retains 361 m Ah/g after 200 cycles at 0.2 C. Even at a high current rate of 5 C, the battery still shows a discharge capacity as high as 155 m Ah/g. The improved electrochemical performance is attributed to the synergy effect of the interconnected and well-designed micro, meso and macroporosity while shortened ions diffusion pathways of such Murray materials accelerate its ionic and electronic conductivities leading to the enhanced electrochemical reaction. The diffusivity coefficient in Se/OHPC can reach a very high value of 1.3 × 10^(-11)cm^(2)/s, much higher than those in single pore size carbon hosts. Their effective volume expansion accommodation capability and reduced dissolution of polyselenides ensure the high stability of the battery. This work, for the first time, established the clear relationship between textural properties of cathode materials and their performance and demonstrates that the concept of the generalized Murray’s law can be used as efficient guidance for the rational design and synthesis of advanced hierarchically porous materials and the great potential of 3D OHPC materials as a practical high performance cathode material for Li-Se batteries.

Atomically dispersed hierarchically ordered porous Fe-N-C single-atom nanozymes for dyes degradation

The development of novel nanozymes for environmental contamination remediation is a worthwhile research direction.However,most of the reported nanozymes cannot degrade efficiently due to the limitation of the internal active sites not being able to come into direct contact with contaminants.Therefore,we reported Fe-N-C single-atom nanozymes(SAzymes)with atomically dispersed FeN4 active sites anchored on a three-dimensional hierarchically ordered microporous-mesoporous-macroporous nitrogen doped carbon matrix(3DOM Fe-N-C)for the degradation of a targeted environmental pollutant(rhodamine B(RhB)).The three-dimensional(3D)hierarchically ordered porous structure may accelerate mass transfer and improve the accessibility of active sites.This structure and high metal atom utilization endow Fe-N-C SAzyme with enhanced tri-enzyme-mimic activities,comprising oxidase-mimic,peroxidase-mimic,and catalase-mimic activities.Based on its excellent peroxidase-mimic activity,3DOM Fe-N-C can degrade RhB by hydroxyl radicals(·OH)generated in the presence of hydrogen peroxide.This study provides a new idea for designing porous Fe-N-C SAzymes for environmental contamination remediation.

Boosting reaction kinetics and shuttle effect suppression by single crystal MOF-derived N-doped ordered hierarchically porous carbon for high performance Li-Se battery

Maximizing the fixing ability of polyselenides to reduce the shuttle effect in Li-Se batteries remains highly challenging.Single crystal metal-organic framework(MOF)-derived N-doped ordered hierarchically porous carbon(SNOHPC)synthesized by a confined crystal growth and template-assisted method demonstrates excellent electrochemical performance as a host material for Li-Se battery.The large number of micropores inherited from the MOF structure provides large space and surface for Se loading and reaction sites,ensuring the high energy density of the battery.The insitu X-ray diffraction(XRD)technique is used to understand the reaction mechanism.The synergy of the interconnected three-scale-level micro-meso-macroporous structure and Ndoped polar sites can buffer the volume expansion,shorten the ion transportation with a very high diffusion coefficient of4.44×10cm^(2)sand accelerate the lithiation/delithiation reaction.Selenium is sufficiently reactive and the polyselenide intermediates are tightly fixed inside the carbon host material,thereby achieving excellent specific capacity,stability,and rate capability.Such a cathode exhibits a very high 2discharge/charge capacity of 658 and 683 mA h g,respectively,and retains a very high capacity of 367 mA h gafter 200 cycles at the current of 0.2 C.Even at the high current of 5 C,a very high discharge capacity of 230 mA h gis obtained.This work provides a new kind of high-performance porous materials with rational pore arrangement applicable for highly efficient energy storage.

Highly efficient electroreduction of CO_(2) by defect single-atomic Ni-N_(3) sites anchored on ordered micro-macroporous carbons

Microporous supports typically fail to fully expose active sites for electrolytes and CO_(2) molecules,and this usually results in low current density for the electrocatalytic CO_(2) reduction reaction(CO_(2)RR).To overcome the biggest obstacle and facilitate commercial applications,defective single-atomic Ni-N_(3) sites anchored to ordered micro-macroporous N-doped carbon(Ni-N/OMC)have been prepared by the pyrolysis of the Ni-ZIF-8@PS(ZIF=zeolitic imidazolate framework)and are intended to provide enhanced CO_(2)RR with a current density at an industrial level.This Ni-ZIF-8@PS is constructed of nickel-based ZIF-8 embedded in the three-dimensional(3D)highly ordered polystyrene spheres(PS).The 3D ordered micro-macroporous architecture of Ni-N/OMC could facilitate the mass transfer of substrates to the accessible defective single-atomic Ni-N_(3) sites through micropores(0.6 nm)and macropores(~200 nm)interconnected by 50 nm channels.In a flow cell,Ni-N/OMC exhibits almost 100.0%CO Faraday efficiency(FECO)between−0.2 and−1.1 V vs.RHE and an industrial level CO partial current density of 208 mA cm^(−2).It has a turnover frequency of 1.5×10^(5) h^(−1) at−1.1 V vs.RHE in 1 M KOH electrolyte,which exceeds that of most reported nickel-based electrocatalysts.This excellent CO_(2)RR performance for Ni-N/OMC makes it a state-of-the-art electrocatalyst for CO_(2)RR.Theoretical calculations show that the defective Ni-N_(3) site can lower the energy of*COOH formation compared with that of the Ni-N4 site,thereby accelerating CO_(2)RR.Ni-N/OMC can also be utilized as a cathodic catalyst in Zn-CO_(2) battery,exhibiting high CO selectivity in the discharge process and excellent stability.This work paves a pathway to rational design of highly efficient electrocatalysts with 3D hierarchically ordered micro-macroporous architecture for CO_(2)RR towards industrial production and commercial applications.