Rational Construction of Hierarchically Porous Fe–Co/N-Doped Carbon/rGO Composites for Broadband Microwave Absorption

Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge.Here,a novel Fe-Co/N-doped carbon/reduced graphene oxide(Fe-Co/NC/rGO)composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Cobased metal organic frameworks(Co-MOF)on the sheets of porous cocoon-like rGO followed by calcination.The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO.The Fe-Co/NC/rGO composite with multiple components(Fe/Co/NC/rGO)causes magnetic loss,dielectric loss,resistance loss,interfacial polarization,and good impedance matching.The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves.Compared with the Co/NC and Fe-Co/NC,the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design.Its minimum reflection loss(RLmin)reaches?43.26 dB at 11.28 GHz with a thickness of 2.5 mm,and the effective absorption frequency(RL≤?10 dB)is up to 9.12 GHz(8.88-18 GHz)with the same thickness of 2.5 mm.Moreover,the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm.This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.

Molybdate intercalated nickel-iron-layered double hydroxide derived Mo-doped nickel-iron phosphide nanoflowers for efficient oxygen evolution reaction

The design of a highly efficient electrocatalyst for oxygen evolution reaction(OER)is of great significance to the clean energy conversion system.Herein,novel Mo-doped NiFe phosphide(Mo-NiFe-P)nanoflowers are developed as robust high-activity catalysts for OER via the phosphidation of MoO_(4)^(2−)intercalated NiFe-layered double hydroxide(NiFe-LDH).The introduction of high valence Mo can significantly promote the catalytic activity of OER because of the strong electronic interactions with Ni and Fe.By tailoring the amount of molyb-date intercalated into NiFe-LDH,the optimal phosphide shows outstanding overpotentials of 261 and 272 mV to drive current densities of 50 and 100 mA cm−2 in 1 mol L−1 KOH.This work demonstrates that the amount of molybdate influences the structure of phosphide prepared by the intercalated LDHs and also affects the elec-trocatalytic behavior.In addition,density functional theory(DFT)calculations show that introducing Mo could alter the intrinsic electronic structure of NiFe-P,which,in turn,could accelerate the reaction kinetics.This approach could be extended to the preparation of other cost-efficient phosphides for OER.