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.

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.

单晶MOF衍生的N掺杂有序等级多孔碳促进反应动力学和穿梭效应的抑制用于高性能锂硒电池

实现多硒化物的最大化固定能力以降低在锂硒电池中的穿梭效应仍然面临很大的挑战性.通过晶体限制生长和模板辅助方法合成的MOF单晶衍生的N掺杂有序分级多孔碳(S-NOHPC)展示了其作为锂硒电池载体材料的优异电化学性能.MOF结构固有的大量微孔为硒的负载提供了大量的空间和表面反应位点,确保了电池的高能量密度.互连的三级微-中-大孔结构和N掺杂极性位点的协同作用可以缓冲体积膨胀,缩短离子传输,其极高扩散系数为4.44×10^(-10)cm^(2)s,加速了锂化/脱锂反应.硒得到了最大限度的激活,多硒化物中间体紧密固定在碳载体材料的内部,从而实现了优异的比容量、稳定性和倍率性能.该正极在0.2 C的电流密度下表现出非常高的第二圈放/充电容量,分别为658和683 mA h g^(-1),并且循环200圈后仍保持367 mA h g^(-1)的高容量.即使在5 C的大电流密度下,其仍可获得230 mA h g^(-1)的高放电容量.该工作为高效储能设备提供了一种具有合理孔隙排列的新型高性能多孔材料.