Ultrafine Fe/Fe3C decorated on Fe-N_(x)-C as bifunctional oxygen electrocatalysts for efficient Zn-air batteries

Efficient bifunctional oxygen electrocatalysts for ORR and OER are fundamental to the development of high performance metal-air batteries.Herein,a facile cost-efficient two-step pyrolysis strategy for the fabrication of a bifunctional oxygen electrocatalyst has been proposed.The efficient non-preciousmetal-based electrocatalyst,Fe/Fe_(3)C@Fe-N_(x)-C consists of highly curved onion-like carbon shells that encapsulate Fe/Fe_(3)C nanoparticles,distributed on an extensively porous graphitic carbon aerogel.The obtained Fe/Fe_(3)C@Fe-N_(x)-C aerogel exhibited superb electrochemical activity,excellent durability,and high methanol tolerance.The experimental results indicated that the assembly of onion-like carbon shells with encapsulated Fe/Fe_(3)C yielded highly curved carbon surfaces with abundant Fe-Nxactive sites,a porous structure,and enhanced electrocatalytic activity towards ORR and OER,hence displaying promising potential for application as an air cathode in rechargeable Zn-air batteries.The constructed Zn-air battery possessed an exceptional peak power density of~147 mW cm^(-2),outstanding cycling stability(200 cycles,1 h per cycle),and a small voltage gap of 0.87 V.This study offers valuable insights regarding the construction of low-cost and highly active bifunctional oxygen electrocatalysts for efficient air batteries.

Molten salt assisted fabrication of Fe@Fe_(SA)-N-C oxygen electrocatalyst for high performance Zn-air battery

Non-noble-metal-based electrocatalysts with superior oxygen reduction reaction(ORR)activity to platinum(Pt)are highly desirable but their fabrications are challenging and thus impeding their applications in metal-air batteries and fuel cells.Here,we report a facile molten salt assisted two-step pyrolysis strategy to construct carbon nanosheets matrix with uniformly dispersed Fe_(3) N/Fe nanoparticles and abundant nitrogen-coordinated Fe single atom moieties(Fe@Fe_(SA)-N-C).Thermal exfoliation and etching effect of molten salt contribute to the formation of carbon nanosheets with high porosity,large surface area and abundant uniformly immobilized active sites.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)image,X-ray absorption fine spectroscopy,and X-ray photoelectron spectroscopy indicate the generation of Fe(mainly Fe_(3) N/Fe)and Fe_(SA)-N-C moieties,which account for the catalytic activity for ORR.Further study on modulating the crystal structure and composition of Fe_(3) N/Fe nanoparticles reveals that proper chemical environment of Fe in Fe_(3) N/Fe notably optimizes the ORR activity.Consequently,the presence of abundant Fe_(SA)-N-C moieties,and potential synergies of Fe_(3) N/Fe nanoparticles and carbon shells,markedly promote the reaction kinetics.The as-developed Fe@Fe_(SA)-N-C-900 electrocatalyst displays superior ORR performance with a half-wave potential(E_(1/2))of 0.83 V versus reversible hydrogen electrode(RHE)and a diffusion limited current density of 5.6 mA cm^(-2).In addition,a rechargeable Zn-air battery device assembled by the Fe@Fe_(SA)-N-C-900 possesses remarkably stable performance with a small voltage gap without obvious voltage loss after500 h of operation.The facile synthesis strategy for the high-performance composites represents another viable avenue to stable and low-cost electrocatalysts for ORR catalysis.

Spatial confinement of zeolitic imidazolate framework deposits by porous carbon nanospheres for dual-atom catalyst towards high-performance oxygen reduction reaction

Dual atom catalysts(DACs),are promising electrocatalysts for oxygen reduction reaction(ORR)on account of the potential dual-atom active sites for the optimized adsorption of catalytic intermediates and the lower reaction energy barriers.Herein,spatial confinement strategy to fabricate DACs with well-defined Fe,Co dual-atom active site is proposed by implanting zeolitic imidazolate frameworks inside the pores of highly porous carbon nanospheres(Fe/Co-SAs-Nx-PCNSs).The atomically dispersed dual-atom active sites facilitate the adsorption/desorption of intermediates.Furthermore,the spatial confinement effect protects metal atoms aggregating.Benefiting from the rich accessible dual-atom active sites and boosted mass transport,we achieve remarkable ORR performance with half-wave potential up to 0.91 and 0.8 V(vs.reversible hydrogen electrode(RHE)),and long-term stability up to 10 h in both alkaline and acidic electrolytes.The remarkably enhanced ORR catalytic property of our as-developed DACs is in the rank of excellence for 1%.The as-developed rechargeable Zn-air battery(ZAB)with Fe/Co-SAs-Nx-PCNSs air cathode delivers ultrahigh power density of 216 mW·cm^(−2),outstanding specific capacity of 813 mAh·g^(−1),and promising cycling operation durability over 160 h.The flexible Zn-air battery also exhibits excellent specific capacity,cycling stability,and flexibility performance.This work opens up a new pathway for the multiscale design of efficient electrocatalysts with atomically dispersed multiple active sites.

Highly active CeO_2 hollow-shell spheres with Al doping

Metal oxide hollow structures are of great inter- est in many current and emerging areas of technology. This paper presents a facile and controlled protocol for the syn- thesis of Al-doped CeO2 hollow-shell spheres （CHS）, where the dopant confers enhanced stability and activity to the ma- terial. These Al-doped CeO2 hollow-shell spheres （ACHS） possess a controllable shell number of up to three, where the sizes of the exterior, middle, and interior spheres were about 250-100 nm,150-50 nm, and 40-10 nm, respectively, and the average shell thickness was -15 nm. The thermal stability of the ACHS structure was enhanced by the homogeneous in- corporation of AI atoms, and more active oxygen species were present compared with those in the non-doped congener. Au NPs supported on ACHS （Au/ACHS） showed superior cat- alytic performance for the reduction of p-nitrophenol. For the same Au NP content, the reaction rate constant （k） of the Au/ACHS was nearly twice that of the non-doped Au/CHS, indicating that AI doping is promising for improving the per- formance of inert or unstable oxides as catalyst supports.

Cobalt hollow nanospheres： controlled synthesis, modification and highly catalytic performance for hydrolysis of ammonia borane

Size tunable cobalt hollow nanospheres with high catalytic activity for the ammonia borane(AB) hydrolysis have been synthesized by using the solvothermal method. The complexation between Co2+and ethylenediamine is observed to be critical for the formation of the cobalt hollow nanospherical structure.The morphology of the cobalt hollow nanospheres can be regulated by adjusting the original ethylenediamine/ethanol volume ratio, reaction time and temperature. Impressively, the magnetic property study reveals that the coercivity of the as-synthesized cobalt hollow nanospheres is much enhanced compared with that of bulk cobalt materials. Meanwhile, Co/Pt bimetal hollow nanospheres(Co Pt HS) and graphene-cobalt hollow composite nanospheres(Co HS-r GO) have also been explored. In comparison with the cobalt hollow nanospheres, both the Co Pt HS and Co HS-r GO show higher catalytic activities and better repeatability for the catalytic hydrogen generation from AB hydrolysis. Moreover, it is noted that these catalysts could be recycled by using the magnetic separation method.

Stable confinement of Fe/Fe_(3)C in Fe,N-codoped carbon nanotube towards robust zinc-air batteries

Catalytic oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)have garnered great attention as the key character in metal-air batteries.Herein,we developed a superior nonprecious bifunctional oxygen electrocatalyst,fabricated through spatial confinement of Fe/Fe_(3)C nanocrystals in pyridinic N and Fe-Nx rich carbon nanotubes(Fe/Fe_(3)C-N-CNTs).During ORR,the resultant electrocatalyst exhibits positive onset pote ntial of 1.0 V(vs.RHE),large half-wave potentials of 0.88 V(vs.RHE),which is more positive than Pt/C(0.98 V and 0.83 V,respectively).Remarkably,Fe/Fe_(3)C-N-CNTs exhibits outstanding durability and great methanol tolerance,exceeding Pt/C and most reported nonprecious metal-based oxygen reduction electrocatalysts.Moreover,Fe/Fe_(3)C-N-CNTs show a markedly low potential at j=10 mA/cm^(2),small Tafel slopes and extremely high stability for OER.Impressively,the Fe/Fe_(3)C-N-CNTs-based Zn-air batteries demonstrate high power density of 183 mW/cm^(2)and robust charge/discharge stability.It is revealed that the spatial confinement effect can impede the aggregation and corrosion of Fe/Fe_(3)C nanocrystals.Meanwhile,Fe/Fe_(3)C and Fe-Nx play synergistic effect on boosting the ORR/OER activity,which provides an important guideline for construction of inexpensive nonprecious metal-carbon hybrid nanomaterials.