A ternary phased SnO_2-Fe_2O_3/SWCNTs nanocomposite as a high performance anode material for lithium ion batteries

A new SnO2-Fe2O3/SWCNTs（single-walled carbon nanotubes） ternary nanocomposite was first synthesized by a facile hydrothermal approach.SnO2 and Fe2O3 nanoparticles（NPs） were homogeneously located on the surface of SWCNTs,as confirmed by X-ray diffraction（XRD）,transmission electron microscope（TEM） and energy dispersive X-ray spectroscopy（EDX）.Due to the synergistic effect of different components,the as synthesized SnO2-Fe2O3/SWCNTs composite as an anode material for lithium-ion batteries exhibited excellent electrochemical performance with a high capacity of 692 mAh·g-1 which could be maintained after 50 cycles at 200 mA·g-1.Even at a high rate of2000 mA·g-1,the capacity was still remained at 656 mAh·g-1.

Influence of different Fe doping strategies on modulating active sites and oxygen reduction reaction performance of Fe, N-doped carbonaceous catalysts

Fe/N/C catalysts,synthesized through the pyrolysis of Fe-doped metal–organic framework (MOF) precursors,have attracted extensive attention owing to their promising oxygen reduction reaction (ORR) catalytic activity in fuel cells and/or metal-air batteries.However,post-treatments (acid washing,second pyrolysis,and so on) are unavoidable to improve ORR catalytic activity and stability.The method for introducing Fe^(3+) sources (anhydrous Fe Cl_(3)) into the MOF structure,in particular,is a critical step that can avoid time-consuming post-treatments and result in more exposed Fe-N_(x) active sites.Herein,three different Fe doping strategies were systematically investigated to explore their influence on the types of active sites formed and ORR performance.Fe-NC(Zn^(2+)),synthesized by one-step pyrolysis of Fe doped ZIF-8 (Zn^(2+)) precursor which was obtained by adding the anhydrous Fe Cl_(3)source into the Zn(NO_(3))_(2)·6H_(2)O/methanol solution before mixing,possessed the highest Fe-N_(x)active sites due to the high-efficiency substitution of Zn^(2+)ions with Fe^(3+) ions during ZIF-8 growth,the strong interaction between Fe^(3+) ions and N atoms of 2-Methylimidazole (2-MIm),and ZIF-8’s micropore confinement effect.As a result,Fe-NC(Zn^(2+)) presented high ORR activity in the entire p H range (p H=1,7,and 13).At p H=13,Fe-NC(Zn^(2+)) exhibited a half-wave potential (E1/2) of 0.95 V (vs.reversible hydrogen electrode),which was 70 m V higher than that of commercial Pt/C.More importantly,Fe-NC(Zn^(2+)) showed superior ORR stability in neutral media without performance loss after 5,000 cycles.A record-high open-circuit voltage(1.9 V) was obtained when Fe-NC(Zn^(2+)) was used as a cathodic catalyst in assembled Mg-air batteries in neutral media.The assembled liquid and all-solid Mg-air batteries with high performance indicated that Fe-NC(Zn^(2+)) has enormous potential for use in flexible and wearable Mg-air batteries.

Defect engineering of single-walled carbon nanohorns for stable electrochemical synthesis of hydrogen peroxide with high selectivity in neutral electrolytes

Hydrogen peroxide(H_(2)O_(2))is one of the most important chemicals,which are commonly used in the paper and pulp industry,water purification and environmental protection[1-3].Most of the commercial available H_(2)O_(2) is produced by the anthraquinone oxidation process,which is environment unfriendly.

Pre-fixing defects in carbon framework for revealing the active sites of oxygen reduction reaction at nitrogen-doped carbon nanotubes

Nitrogen-doped carbon-based materials are promising non-platinum group metal electrocatalysts for the oxygen reduction reaction(ORR).Understanding their ORR active sites is vital for the rational design and development of nitrogen-doped carbon-based electrocatalysts with enhanced catalytic efficiency and selectivity.However,the conclusive analysis of the ORR mechanism of nitrogen-doped carbon-based electrocatalysts remains a grand challenge because the catalysts have a complex inhomogeneous structure.Here,we elucidate this problem using nitrogen-doped carbon nanotubes framework catalysts with fixed defect concentrations prepared by pre-thermal treatment at a low temperature.The generation of defects under high-temperature treatment was effectively suppressed to enable a simple model for ORR mechanism study.A correlation between ORR pathways and the different nitrogen species in the nitrogen-doped carbon catalysts was revealed through a combination of structural and electrochemical properties investigations.Besides,our results also demonstrate the importance of defects for ORR.We believe that the results will provide instructive guidance for designing and developing novel carbon nanomaterials for ORR.

Approaching Superior Potassium Storage of Carbonaceous Anode Through a Combined Strategy of Carbon Hybridization and Sulfur Doping

Carbonaceous materials are promising anode candidates for potassium-ion batteries(PIBs)given its high conductivity,stable property,and abundant resource,while its practical implementation is still hampered by its limited capacity and inferior rate behavior.Herein,we report a superior carbonaceous anode through a combined strategy of carbon hybridization and heteroatom doping.In this composite,hollow carbon spindles(HCS)were anchored on the surface of graphene(G)followed with sulfur doping treatment,aiming to integrate the high conductivity of graphene,the good structure stability of HCS,and the S doping-induced ample active sites.As a PIB anode,the S-G@HCS composite can display high capacity(301 mAh g^(-1)at 0.1 A g^(-1)after 500 cycles)and long-term cyclability up to 1800 cycles at 2 A g^(-1).Impressively,it can deliver an outstanding rate capacity of 215 mAh g^(-1)at 10 A g^(-1),which is superior to most carbon anodes as-reported so far for PIBs.Experimental and theoretical analysis manifests that the construction of graphene/amorphous carbon interface as well as S doping enables the regulation of electronic structure and ion adsorption/transportation properties of carbonaceous material,thus accounting for the high capacity and superior rate capability of S-G@HCS composite.

A MOF-to-MOF conversion assisted formation of hierarchical hollow Zn-Co_(1-x)S/C@C composite for efficient potassium-ion storage

Hollow structured composite can enhance the structural stability of metal sulfide anode by accommodating its volume variation,while the performance is still hindered by its poor electron/ion conductivity.Herein,we develop a hier-archical hollow structure to achieve superior electrochemical performance,from which a MOF-to-MOF conversion is utilized to generate hollow Zn-Co_(1-x)S/C composite followed with additional carbon coating layer.For potassium storage,as-prepared hollow Zn-Co1.xS/C@C composite displays high capacities of 375 mA h g^(-1)after 100 cycles at 0.2 A g^(-1)and 201 mA h g^(-1)after 500 cycles at 1 A g^(-1).Moreover,it also manifests outstanding rate capability of 200 mA h g^(-1)at 10 A g^(-1),outperforming hollow Co_(1-x)S@C and majority of the reported cobalt-based anodes.With illustration by kinetics analysis and theoretical calculation,both of Zn doping and internal carbon matrix are conductive to promote the charge transportation ability of Co_(1-x)S,thus accounting for the good cycling behavior and excellent rate capacity of hierarchical hollow Zn-Co1.xS/C@C composite.

Monodispersed SWNTs Assembled Coating Layer as an Alternative to Graphene with Enhanced Alkali-ion Storage Performance

Graphene coating is commonly used to improve the performance of electrode materials,while its steric hindrance effect hampers fast ion transport with compromised rate capability.Herein,a unique single-walled carbon nanotubes(SWNTs)coating layer,as an alternative to graphene,has been developed to improve the battery behavior of iron-based anodes.Benefiting from the structure merits of mesoporous SWNTs layer for fast electron/ion transport and hollow Fe_(3)O_(4) for volume accommodation,as-prepared Fe_(3)O_(4)@SWNTs exhibited excellent lithium storage performance.It delivers a high capacity,excellent rate capability,and long lifespan with capacities of 582 mA·h·g^(-1) at 5 A·g^(-1) and 408 mA·h·g^(-1) at 8 A·g^(-1) remained after 1000 cycles.Such performance is better than graphene-coated Fe_(3)O_(4) and other SWNT-Fe_(3)O_(4) architectures.Besides,SWNTs coating is also used to improve the sodium and potassium storage performance of FeSe_(2).The kinetics analysis and ex-situ experiment further reveal the effect of SWNTs coating for fast electron/ion transfer kinetics and good structure stability,thus leading to the superior performance of SWNTs-coated composites.

Boosting Stable and Fast Potassium Storage of Iron Sulfide through Rational Yolk-Shell Design and Ni Doping

Metal sulfides have been regarded as promising anodes for potassium-ion batteries(PIBs)due to their high theoretical capacities,while the performance is limited by their intrinsic poor conductivity and large volume fluctuation during the insertion/extraction of large potassium ion.Herein,the battery performance of iron sulfide anode is significantly enhanced through yolk-shell(Y-S)structure design and nickel doping,aiming to realize good structure stability and superior electron/ion transportation.For potassium storage,as-prepared Y-S Ni-FeS_(2)@C shows excellent cyclic performance and sustains high capacities of 328 mA h g^(-1)after 100 cycles at 0.2 A g^(-1)and 226 mA h g^(-1)after 1000 cycles at 1 A g^(-1).Especially,it displays a superior rate capacity of 200 mA h g^(-1)at 20 A g^(-1),higher than that of Y-S FeS_(2)@C and most as-reported metal sulfide anodes for PIBs.The experimental analysis and theoretical calculation illuminate the effect of Ni-doping on decreasing the particle size of iron sulfide and enhancing the ion/electron transport ability,thus accounting for the exceptional rate capability of Y-S Ni-FeS_(2)@C composite.

Highly Dispersive Metal Atoms Anchored on Carbon Matrix Obtained by Direct Rapid Pyrolysis of Metal Complexes

The oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are critical in energy conversion and storage devices.Single-atom catalysts(SAC)with atomic utilization efficiency are among the most promising candidates for oxygen reactions.Focusing on the controllable and efficient synthesis of SACs,we develop a direct rapid pyrolysismethod that shortens the synthesis process from several hours to 1 min.