Tuning interface mechanism of FeCo alloy embedded N,S-codoped carbon substrate for rechargeable Zn-air battery

The interface mechanism between catalyst and carbon substrate has been the focus of research.In this paper,the FeCo alloy embedded N,S co-doped carbon substrate bifunctional catalyst(FeCo/S-NC)is obtained by a simple one-step pyrolysis strategy.The experimental results and density functional theory(DFT)calculation show that the formation of FeCo alloy is conducive to promoting electron transfer,and the introduction of S atom can enhance the interaction between FeCo alloy and carbon substrate,thus inhibiting the migration and agglomeration of particles on the surface of carbon material.The FeCo/SNC catalysts show outstanding performance for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).FeCo/S-NC shows a high half-wave potential(E_(1/2)=0.8823 V)for ORR and a low overpotential at 10 mA cm^(-2)(E_(j=10)=299 mV)for OER.In addition,compared with Pt/C+RuO_(2) assembled Zn-air battery(ZAB),the FeCo/S-NC assembled ZAB exhibits a larger power density(198.8 mW cm^(-2)),a higher specific capacity(786.1 mA h g_(zn)~(-1)),and ultra-stable cycle performance.These results confirm that the optimized composition and the interfacial interaction between catalyst and carbon substrate synergistically enhance the electrochemical performance.

FeCo alloy@N-doped graphitized carbon as an efficient cocatalyst for enhanced photocatalytic H2 evolution by inducing accelerated charge transfer

Cocatalysts play important roles in improving the activity and stability of most photocatalysts.It is of great significance to develop economical,efficient and stable cocatalysts.Herein,using Na2CoFe(CN)6 complex as precursor,a novel noble-metal-free FeCo@NGC cocatalyst(nano-FeCo alloy@N-doped graphitized carbon) is fabricated by a simple pyrolysis method.Coupling with g-C3 N4, the optimal FeCo@NGC/g-C3N4 receives a boosted visible light driven photocatalytic H2 evolution rate of 42.2 μmol h-1, which is even higher than that of 1.0 wt% Pt modified g-C3N4 photocatalyst.Based on the results of density functional theory(DFT) calculations and practical experiment measurements,such outstanding photocatalytic performance of FeCo@NGC/g-C3N4 is mainly attributed to two aspects.One is the accelerated charge transfer behavior,induced by a photogene rated electrons secondary transfer performance on the surface of FeCo alloy nanoparticles.The other is related to the adjustment of H adsorption energy(approaching the standard hydrogen electrode potential) by the presence of external NGC thin layer.Both factors play key roles in the H2 evolution reaction.Such outstanding performance highlights an enormous potential of developing noble-metal-free bimetallic nano-alloy as inexpensive and efficient cocatalysts for solar applications.

FeCo alloy catalysts promoting polysulfide conversion for advanced lithium-sulfur batteries

Lithium sulfur batteries(LSBs)draw extensive interest because of the ultra-high capacity and low material cost.However,the sluggish lithium polysulfides(LIPSs)conversion processes are detrimental to cycle stability and rate capability,inhibiting the commercial application of LSBs.Here we present the well-designed Fe Co alloy catalysts anchored on porous carbon(FeCo-C)as sulfur host to improve the electrochemical performance by accelerating the conversion reactions.The FeCo alloy demonstrates high catalytic effect and strong adsorption capability of LIPSs,in which potential polarization can be greatly decreased and"shuttle effects"can be largely avoided.As a result,the obtained S/Fe Co-C composites show an initial specific capacity of 791.9 m Ah g^-1 at a large current density of 2 C and maintain 502.5 mAh g^-1 even after 500 cycles.Moreover,720 m Ah g^-1(corresponding to 70%retention)can be achieved after 100 cycles at 0.2 C with a high sulfur content of 80 wt%,enabling high sulfur utilization.This work not only provides a new insight to investigate the conversion kinetics of Li PSs,but also opens up a new avenue for advanced lithium sulfur batteries.

Nucleation of Cold Rolled FeCo Alloy during Annealing and Its Influence on the Formation of Recrystallization Texture

The orientation distribution of recrystallization grains formed during annealing, as well as their misorientation relationship to the deformation matrix in cold rolled FeCo alloy have been investigated. It was found that most of the recrystallization nuclei were located near the boundary area with rather random orientations, and their misorientation angles to the deformation matrix were generally very high. However a few nuclei were also observed inside the deformation grains, to which they had very similar orientations. Therefore the misorientation angles between the nuclei and the deformation matrix were generally very low. The orientation and the misorientation distributions of the nuclei have very strong influence on the recrystallization process which could result in a very weak recrystallization texture. The corresponding mechanism is discussed.

FeCo alloy/N,S co-doped carbon aerogel derived from directionalcasting cellulose nanofibers for rechargeable liquid flow and flexible Zn–air batteries

Bifunctional oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)electrocatalysts with the advantages of excellent activity and stability are the vital components of air cathodes for rechargeable Zn–air batteries(ZABs).Herein,the carbon aerogel with honeycomb-like structure,N and S double doping and loaded with FeCo alloy nanoparticles(NSCA/FeCo)was prepared successfully as cathodes for rechargeable liquid flow and two-dimensional flexible ZABs by clever directional casting.The interaction between the bimetallic alloy and the double-doped carbon with specifical structure,large surface,great conductivity endows NSCA/FeCo with effective ORR/OER active sites and small charge/mass transport barrier,thus achieving outstanding bifunctional catalytic performance.The NSCA/FeCo displays a half-wave potential of+0.85 V(vs.reversible hydrogen electrode(RHE))for ORR and an overpotential of 335 mV at a current density of 10 mA·cm^(−2)for OER,which is even comparable to the performance of noble-metal catalysts in relevant fields(Pt/C for ORR and RuO_(2)for OER).Consequently,the rechargeable liquid flow ZABs assembled with NSCA/FeCo showed excellent performance(maximum power density:132.0 mW·cm^(−2),specific capacity:804.5 Wh·kg^(−1)at 10 mA·cm^(−2),charge and discharge cycle stability of more than 250 cycles).Furthermore,the flexible NSCA/FeCo-based ZABs have a maximum power density of 43.0 mW·cm^(−2),outstanding charging–discharge stability of more than 450 cycles,exhibit good flexibility under different bending conditions.Therefore,this work has provided an efficient bifunctional electrocatalyst for OER/ORR and a promising strategy of air cathodes for rechargeable and wearable ZABs.

Texture Evolution in Heavily Cold-Rolled FeCo-2V Alloy during Annealing

The recrystallization texture evolution in heavily cold-rolled （93%） FeCo-2V alloy with annealing temperature and time was investigated by X-ray diffraction and electron backscatter diffraction. It was found that the orientation density of α-fiber texture component fluctuates with increasing annealing temperature and time. The transmission electron microscopy images show that abundant precipitates appear inside the recrystallized grains and around the grain boundaries. The amount and size of the precipitates also vary with annealing temperature and time. The enhancement of the α-fiber coincides well with the increase of number density of fine precipitates, indicating that the fine precipitates facilitate the development of α-fiber. The annealing texture evolution observed in the FeCo alloy could be attributed to the facilitating effect of the precipitates on the development of α-fiber and the ordering process.

A dual metal-organic framework strategy for synthesis of FeCo@NC bifunctional oxygen catalysts for clean energy application

Developing high efficient bifunctional oxygen electrocatalysts for clean energy applications like Zin-air battery(ZAB)is highly desired,because it would reduce the cost and speed up the practical application of ZAB.Here we use a dual metal-organic framework(MOF)synthesis strategy to prepare the N-doped carbon supported bimetallic FeCo nanoparticle catalysts(marked as FeCo@NC)by pyrolysis of Zn CoZIF/MIL-101(Fe)composite.The FeCo@NC exhibits remarkable electrocatalytic activity for ORR with half-wave potential of 0.89 V vs.the reversible hydrogen electrode(RHE)and robust durability for both ORR and OER(oxygen reduction reaction and oxygen evolution reaction),which is attributed to the generation of Fe_(0.26)Co_(0.74) crystalline phase and mesopores due to the dual-MOF synthesis strategy.The rechargeable ZAB based on FeCo@NC air electrode shows a maximum energy density of139.6 mW·cm^(-2) and excellent cyclic stability over 130 h,significantly surpassing the Pt and Ir-based ZAB.The present work provides a useful dual-MOF synthesis strategy for preparing high-performance multifunctional catalysts for ORR,OER and hydrogen evolution reaction(HER).

Fe48Co52 Alloy Nanowire Arrays： Effects of Magnetic Field Annealing

The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances （Di=30-60 nm） and wire diameters （Dw=22-46 nm） were investigated in detail. It was found that the array＇s best annealing temperature and crys- talline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious influence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variation of the array＇s magnetic properties after magnetic field annealing.