NiFe Nanoparticles Research Articles

Fe-Ni-Doped Graphene Oxide for Uranium Removal—Kinetics and Equilibrium Studies

In this study, graphene oxide (GO) was prepared using modified Hummer’s method and doped with Fe-Ni nanoparticles. Morphological characterization of the Fe-Ni nanoparticles showed flake-like structure correlating to taenite phase, while Raman spectroscopy suggested that graphene oxide was multi-layered. Batch adsorption experiments were performed to determine the effect of solution pH, initial uranium (VI) concentration, adsorbent dosage, contact time, and specific anions (SO42− and NO32−) on the adsorption of U (VI). Solution pH had significant effect on U (VI) sorption on Fe-Ni/GO, with maximum removal of 98.4% at pH 4, while it was 98% at pH 8 for GO. Sorption kinetics revealed fast adsorption within 15 min. The kinetic and equilibrium data was evaluated using pseudo-first-order, pseudo-second-order, Elovich, Langmuir, Freundlich, and Temkin models. The mechanism of U (VI) sorption appeared to be a combination of chemisorption and possible pore diffusion of the U (VI) moieties to the porous structure of GO and Fe-Ni/GO. Overall, Fe-Ni/GO was a better adsorbent than GO with higher sorption capacities. U (VI) sorption on GO and Fe-Ni/GO followed pseudo-second-order reaction kinetics (R2 > 0.99). Good fit to Langmuir isotherm model (R2 > 0.98) suggested favorable monolayer adsorption, with a maximum U (VI) adsorption capacity on Fe-Ni/GO to be 25.64 mg/g. Moderate to insignificant effect of specific anions even at high concentrations on U (VI) removal capacities makes Fe-Ni/GO an excellent candidate.

One-step preparation of a N-CNTs@Ni foam electrode material with the co-production of H2 by catalytic reforming of N-containing compound of biomass tar

Carbon nanotubes (CNTs) can be formed during catalytic reforming of hydrocarbons with H2 co-production over Ni-based catalysts. Normally, the formed CNTs need to be separated from original catalysts in order to be coated on the substrates to make high performance electrodes. To simplify the traditional preparation process, a novel one-step method for simultaneously producing a CNTs electrode material and H2 was proposed. A Ni-Fe modified Ni foam (Ni-Fe/NF) was chosen as both catalyst and electrode substrate to in situ grow nitrogen-doped carbon nanotubes (N-CNTs) during catalytic reforming of pyrrole. Pyrrole was selected as an N-containing model compound of biomass tar. The results showed that Ni-Fe nanoparticles on Ni-Fe/NF catalyst remarkably improved the H2 production and pyrrole conversion, which increased by more than 20 times than those of fresh Ni foam. Besides, a significant amount of multi-walled CNTs with more than 40 graphite layers grew on the surface of spent catalyst and their diameters were mainly from 10 nm to 20 nm. N element was detected on the formed CNTs and the Graphitic-N was the main type of N-doping. The spent catalyst (N-CNTs@Ni foam) can be directly used as a composite electrode material with high performance and stability. Its electrochemical capacitance reached 855 mF/cm2 at a current density of 5 mA/cm2 and remained over 95% after 10,000 cycles.

Scalable synthesis of Fe3N nanoparticles within N-doped carbon frameworks as efficient electrocatalysts for oxygen reduction reaction

Reasonable design and scalable preparation of low-cost, effective and durable electro-catalysts as substitutes to expensive Pt-derived catalysts for oxygen reduction reaction (ORR) is highly desired toward the progress of future sustainable energy storage devices. In this work, we scalably prepare a highly active ORR electrocatalyst which consists of both Fe3N nanoparticles and Fe-N-C active sites in N-doped carbon frameworks (named as Fe3N/Fe-N-C) and derives from walnut shells as precursors followed by iron ion incorporation and a pyrolysis process in NH3 atmosphere. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopic (XPS) measurements strongly evidence the coexistence of Fe3N nanoparticles and iron-nitrogen-carbon active sites. Benefiting from the synergistic mechanism between Fe3N nanoparticles and Fe-N-C sites in N-doped carbon frameworks, the resultant catalyst presents desirable ORR performance with impressive Eonset, E1/2, higher long-term stability, and satisfactory resistance to methanol interference, overtopping commercial Pt/C catalyst. The present research not only proposes a cost-effective and available ORR electro-catalyst to substitute Pt-based catalysts, but also provides a reliable and versatile technology to realize large-scale preparation for practical applications.

Surpassing electrocatalytic limit of earth-abundant Fe4+ embedded in N-doped graphene for (photo)electrocatalytic water oxidation

Abstract Developing highly active, cost-effective, and environmental friendly oxygen evolution reaction (OER) electrocatalysts facilitates various (photo)electrochemical processes. In this work, Fe3N nanoparticles encapsulated into N-doped graphene nanoshells (Fe3N@NG) as OER electrocatalysts in alkaline media were reported. Both the experimental and theoretical comparison between Fe3N@NG and Fe3N/NG, specifically including in situ Mossbauer analyses, demonstrated that the NG nanoshells improved interfacial electron transfer process from Fe3N to NG to form high-valence Fe4+ ions (Fe4+@NG), thus modifying electronic properties of the outer NG shells and subsequently electron transfer from oxygen intermediate to NG nanoshells for OER catalytic process. Meanwhile, the NG nanoshells also protected Fe-based cores from forming OER inactive and insulated Fe2O3, leading to high OER stability. As a result, the as-formed Fe4+@NG shows one of the highest electrocatalytic efficiency among reported Fe-based OER electrocatalysts, which can as well highly improve the photoelectrochemical water oxidation when used as the co-catalysts for the Fe2O3 nanoarray photoanode.

Irregularly Shaped Iron Nitride Nanoparticles as a Potential Candidate for Biomedical Applications: From Synthesis to Characterization.

Magnetic nanoparticles (MNPs) have been extensively used in drug/gene delivery, hyperthermia therapy, magnetic particle imaging (MPI), magnetic resonance imaging (MRI), magnetic bioassays, and so forth. With proper surface chemical modifications, physicochemically stable and nontoxic MNPs are emerging contrast agents and tracers for in vivo MRI and MPI applications. Herein, we report the high magnetic moment, irregularly shaped γ′-Fe4N nanoparticles for enhanced hyperthermia therapy and T2 contrast agent for MRI application. The static and dynamic magnetic properties of γ′-Fe4N nanoparticles are characterized by a vibrating sample magnetometer (VSM) and a magnetic particle spectroscopy (MPS) system, respectively. Compared to the γ-Fe2O3 nanoparticles, γ′-Fe4N nanoparticles show at least three times higher saturation magnetization, which, as a result, gives rise to the stronger dynamic magnetic responses as proved in the MPS measurement results. In addition, γ′-Fe4N nanoparticles are functionalized with an oleic acid layer by a wet mechanical milling process. The morphologies of as-milled nanoparticles are characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and nanoparticle tracking analyzer (NTA). We report that with proper surface chemical modification and tuning on morphologies, γ′-Fe4N nanoparticles could be used as tiny heating sources for hyperthermia and contrast agents for MRI applications with minimum dose.

Direct Synthesis of Ammonia from N2 and H2O on Different Iron Species Supported on Carbon Nanotubes using a Gas‐Phase Electrocatalytic Flow Reactor

AbstractGreen NH3 production by direct electrocatalytic synthesis from N2 and H2O is still a challenging reaction, which requires us to better understand the nature of the active materials. We show here that iron oxide (Fe2O3) nanoparticles (supported over carbon nanotubes, CNTs) become more active than the corresponding samples after reduction to form Fe‐ or Fe2N‐supported nanoparticles, both indicated as active species in the thermal catalytic reduction of N2 to ammonia. Characterization data, however, indicate that even for these Fe‐ and Fe2N−CNT samples, obtained from Fe2O3−CNT by reduction in H2 or NH3 at 500 °C, the active species responsible for N2 reduction reaction (NRR) at low applied potential (−0.5 V vs RHE) are the same, that is, small (<1–2 nm) iron oxide nanoparticles that are not detected by XRD, but evidenced by XPS and which amount could be correlated to the rate of ammonia formation. This species is stable for at least 24 h of electrocatalytic flow tests. However, at higher applied potentials, sintering/transformation of this species occurs, with loss of the electrocatalytic activity, and Fe2N nanoparticles may also be reduced in situ, forming ammonia, but with irreversible deactivation.

Protein-mediated synthesis of Fe3N nanoparticles embedded in hierarchical porous carbon for enhanced reversible lithium storage

The development of cost-effective electrode materials with high electrochemical performance is of important significance for the large-scale application of lithium-ion batteries. Herein, a novel electrode based on Fe3N nanoparticles anchoring on hierarchical porous carbon (C/Fe3N) is successfully synthesized by a freeze drying and subsequent in-situ nitridation process, using egg white protein as an intrinsic carbon and nitrogen source. The carbon matrix can buffer volume change of Fe3N nanoparticles and improve the electrical conductivity, while Fe3N nanoparticles in the carbon matrix can shorten the diffusion length of Li+. The C/Fe3N electrode displays a reversible capacity of 1007 mA h g−1 at 0.2 A g−1 after 150 cycles. It also delivers a prolonged cycling stability at a high current density of 5 A g−1, and retains a high reversible capacity of 444.8 mA h g−1 after 1500 cycles. This work provides a green and facile approach to design and fabricate Fe3N-based anode materials for lithium-ion batteries.

Synthesis of <i>L</i>1<sub>2</sub>-FeNi Nanoparticles by Nitrogen Insertion and Topotactic Extraction Method

Synthesis of <i>L</i>1<sub>2</sub>-FeNi Nanoparticles by Nitrogen Insertion and Topotactic Extraction Method

(Keynote) Noble-Metal-Free Nanostructured and Graphene Supported Electrocatalysts for Water Splitting

Clean hydrogen production through water splitting is a direct and promising sustainable energy pathway to access and store non-fossil chemical fuels. Synthetic design strategies to access low cost, robust and high performance noble metal-free electrocatalysts are vital for forthcoming water splitting applications. To accomplish this goal, the nanoscale design of multifunctional catalysts based on cost-effective graphene supports, hollow nano-architectures and well-coordinated hybrid organic-inorganic structures has been attracting increasing research interest because of the flexible tuning options of their electronic states, chemical composition and local coordination environments.Over the last years, we have been implementing systematic investigations based on synthetic design, spectroscopy approaches and computational modeling toward the understanding of the mechanism of action in a series of novel, robust and efficient bi-functional electrocatalysts.Recently, we explored synergistic effects of NiFe alloys encapsulated into N-doped carbon nanotubes (N-CNTs) supported on reduced graphene (rGO) nanoshets for overall water splitting.[1] This so-called NiFe-N-CNT-rGO electrocatalyst was synthesized through a direct and flexible strategy using g-C3N4 as precursor, where thermally reduced NiFe nanoparticles act as surface nucleation sites for C species to assist N-CNT growth through an unconventional reduction-nucleation-growth mechanism. The catalyst has a low overpotential of 270 mV for oxygen evolution reaction (OER), being superior in performance to a wide range of reported noble-metal-free catalysts. As revealed from density functional theory (DFT) calculations, N-doping and charge transfer at the CNT walls tune the free energy in the electronic structure toward adsorption of intermediates, which greatly enhanced catalytic performance. This synthetic strategy not only leads to excellent performance and opens up new avenues for other carbon-supported alloy catalysts, but its scalability and easy applicability also render it quite promising for large-scale water splitting applications.In parallel, we explored molecular strategies to conjugate single active sites of metal-phthalocyanine molecules MPc (M=Ni, Co, Fe) on GO.[2] We aim for a thorough understanding of the role of the local coordination environment around the single metal site in the synergistic mechanisms and the catalytic performance. With an advanced combination of ADF (annular dark field)-STEM, operando X-ray absorption spectroscopy and DFT calculations, we observed changes in the electronic and local structure environment of MPc-GO under operando electrochemical OER conditions. Single active metal Ni, Co, Fe sites attain high valence states due to chemisorbed OH− species upon catalytic activation, while the local orders suffer from structural distortion. These changes in the electronic and structural properties lead to the formation of HO-M-N4 moieties with high OER reactivity under operando conditions. These results provides new insight into the fundamental understanding of structure-performance relationships for single active site catalysts.Likewise, we studied hollow transition metal sulfide nanoboxes synthesized through anion exchange processes[3] between S2- and CN- species that lead to formation of Prussian blue (PB), M-S@PB (M=Co, Fe, Ni) heterostructures. We found that the high performance of those nanostructures arises from in situ formation of active Co-Fe oxide/hydroxide species during OER, attaining a superior performance compared to noble-metal-catalysts such as RuO2, with low overpotential of 286 mV and high durability over longer operational periods. The flexible tuning options of the electronic, chemical and local-atomic coordination of those nanostructures render them promising hybrid catalysts for dual OER and HER over an extended pH range.We have further explored new soft templating strategies for the first 1D cobalt coordination polymer electrocatalyst with bio-inspired features, and we applied state-of-the-art analytical techniques and computational modeling to monitor its formation in situ and to unravel its structure.[4] The highly durable 1D-cobalt coordination polymer catalyst implements strategies to transfer key motifs of inorganic materials into a hydrogen bonded ligand environment, namely the embedment of the essential {H2O-Co2(OH)2-OH2} edge-site motif of cobalt oxide catalysts into a flexible and robust organic matrix. While this unconventional catalyst shows exceptional performance in commercial alkaline electrolyzers and organic transformations, its flexible structure offers new pathways toward the rational design of mixed molecular-solid disordered catalysts.[1] W. Wan, S. Wei, J. Li, C. A. Triana, Y. Zhou, G. R. Patzke, J. Mater. Chem. A 2019 (7) 15145.[2] W. Wan, C. A. Triana, J. Lan, J. Li, C. S. Allen, Y. Zhao, M. Iannuzzi, G. R. Patzke, in preparation.[3] Y. Zhao, C. K. Mavrokefalos, P. Zhang, R. Erni, J. Li, C. A. Triana, G. R. Patzke, submitted.[4] C.A. Triana, R. More, A. J. Bloomfield, P. V. Petrovic, S. G. Ferroon, G. Stanley, S. D. Zaric, T. Fox, E. N. Brothers, S. W. Sheehan, P. T. Anastas, G. R. Patzke, Matter 2019 (1) 1354.

(Keynote) Electrochemical Conversion of Sustainable Energy

In this presentation, I will give an overview of some our recent progress in making nanoparticles in relation to electrochemical conversion of sustainable energy [1]. In the first case it will be used to elucidate size dependence and efficiency for catalysts related to the Water splitting i.e. Hydrogen- and in particular Oxygen-evolution reaction (OER) which is the limiting reaction and evaluate the scalability of scarce and expensive elements like the Pt-group metal under acidic conditions [2-4]. We shall discuss caveats of testing catalysts for water splitting [4] and investigate size dependence and isotope labelled experiments will be presented for NiFe nanoparticles for oxygen evolution under alkaline conditions [5]. Here we shall demonstrate a new principle for dynamic detection of gas evolution [6] allowing for a clear distinction between redox states and actual OER by simply measuring the amount of oxygen generated. This will be further pursued for OER catalysis on both Ir and Ru [7] and in the latter case down to 90 mV overpotential [8]. The change of Tafel slopes over many orders of magnitude in current density and mechanisms shall be discussed. If time allow we shall also discuss some of these catalysts used in connection with PEC [9].

Synthesis of Sargassum char-supported Ni-Fe nanoparticles and its application in tar cracking during biomass pyrolysis

Ni-Fe nanoparticles (NPs) supported on biomass char were synthesized by a pyrolysis method using an abundant and fast-growing seaweed biomass (Sargassum) as the precursor for biomass tar cracking applications. With the presence of Ni and Fe ions, the surface area of the prepared SC@0.0.05Ni-Fe and SC@0.1Ni-Fe was larger than 200 m2 g−1 with unique honeycomb-like structures, which was conducive to improving the absorption capacity of the catalyst to tar molecules, enhancing the interaction between tar molecules and active sites, and prolonging the reaction time. Well-dispersed Ni NPs and FeNi3 NPs were in situ formed on the surface of the char support during Sargassum pyrolysis. At a low temperature of 600 °C, the fresh SC@0.1Ni-Fe reached a high tar conversion efficiency of 90.07% with a significant increase in the syngas yield. The yields of the combustible gas components (H2, CO, and CH4) were significantly improved as a result of the tar cracking. After five times successive reuse under the same conditions, the SC@0.1Ni-Fe was able to maintain the tar conversion efficiency at a level of higher than 80%. The structure of the char-supported Ni-Fe catalysts was well retained with the change of the honeycomb-like structure to a certain extent, ensuring the high stability of the catalyst.

Ni3Fe nanoparticles enclosed by B-doped carbon for efficient bifunctional performances of oxygen and hydrogen evolution reactions

Abstract The fabrication of highly active and environmentally friendly electrocatalysts for both oxygen and hydrogen evolution reactions is essential for the improvement of energy generation. In this study, a one-pot synthesis of boron-doped carbon-enclosed Ni3Fe nanoparticles with bifunctional activity for oxygen and hydrogen evolution reactions is reported. The as-fabricated Ni3Fe@BC displays higher OER and HER electrochemical activities in an alkaline media, thereby suggesting a synergy between the Fe and Ni components. Ni3Fe@BC that was carbonized at 500 °C shows relatively small overpotentials of 280 mV and 0.33 V at a current density of 10 mA cm−2 for OER and HER, respectively. Chronoamperometric testing of the nanoparticles for both OER and HER activity revealed promising stability for 20 h. The catalytic performance of Ni3Fe@BC-500 °C is attributed to the doping outcome of boron (B) and the synergistically bonded metal ions of interest (Fe + Ni), which may have enhanced the catalytic sites. The one-pot fabrication from cheap component sources renders the as-fabricated Ni3Fe@BC highly promising for OER and HER electrocatalysis applications.

Rapid microwave-assisted preparation of high-performance bifunctional Ni3Fe/Co-N-C for rechargeable Zn-air battery

Precious metal-free bifunctional catalysts offer scalable possibilities for achieving oxygen cathodes in rechargeable metal-air batteries. Literature thus far suggests that the oxygen reduction and evolution reactions (i.e ORR and OER) take place at different active sites. However, the design and preparation of oxygen electrocatalysts with high-performance is still a great challenge. This work develops a general approach to introduce a nanoparticle that offers oxygen evolution reaction sites onto an oxygen reduction reaction catalyst via rapid microwave treatment. The metal–organic frameworks (Co, ZIF-8) derived Co-N-C with high ORR performance is employed as a support to homogeneously disperse OER active Ni3Fe nanoparticles. Potentials of 1.54 V and 0.79 V have been achieved at current densities of 10 mA cm−2 for OER and 3 mA cm−2 toward ORR, respectively. The developed rechargeable Zn-air battery assembled with Ni3Fe/Co-N-C as an oxygen-electrode exhibits superior efficiency and robust durability, exceeding that of commercial Pt/C + IrO2. Furthermore, the satisfactory activity of our fabricated wristband shows the successfully practical application of flexible Zn-air batteries for wearable devices.

Exsolution of nickel alloys anchored nanoparticles on perovskite oxides for CO oxidation

Noble metals notably platinum (Pt), is a major element of heterogeneous catalysts, excel in catalysing an extensive number of important catalytic reactions in chemical and automotive industries. Since the increased use of these metals is severely limited because of their high cost and scarcity’s, there is therefore an urgent need for the search of alternative transition metal catalysts that are cheaper and more widely available. This can only be practical if the main drawbacks of these transition metals can be impeded for instance the agglomeration of particles under high temperatures operational conditions with their activity enhanced, such that they can directly replace Pt on a weight-to-weight basis. The exsolution of metallic nanoparticles mainly nickel (Ni) at the surface of perovskite oxides in situ has shown remarkable catalytic activity and durability towards carbon monoxide (CO) and nitric oxide (NO) oxidation and in fuel cells. In this study, for CO oxidation reaction, the catalytic capabilities of exsolved Ni nanoparticles can be further enhanced when iron (Fe) and cobalt (Co) are co-exsolved with Ni, as FeNi and CoNi alloy nanoparticles, forming mixed oxide nanoparticles. FeNi alloy nanoparticles exhibit almost ten times site activities as compared to the Ni nanoparticles, owing to the oxide layer formation which then aided the oxidation of CO. Interesting enough, the CoNi alloy nanoparticles exhibit slightly different morphological and chemical transformation due to the difference in oxidation mechanism and the degree of oxidation, which reveal greater site activities towards CO oxidation. These nanoparticles were also subjected to additional compressive strain when they expanded as a result of them being pinned to the support. These results pave the way for new approach in altering the activity of the exsolved materials for various reactions.

Rational design of hybrid Fe7S8/Fe2N nanoparticles as effective and durable bifunctional electrocatalysts for rechargeable zinc-air batteries

Rechargeable zinc-air batteries are promising next-generation energy storage systems due to their large energy density and high safety. However, air-cathodes based on Pt/C and RuO2 suffer from poor catalytic activity and stability in rechargeable zinc-air batteries. Here, we report novel bifunctional Fe7S8/Fe2N nanoparticle (Fe7S8/Fe2N NPs) electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) by carbonizing the metal-organic framework precursors. Due to the synergistic function between the Fe7S8 and Fe2N with high conductivity and high electrochemical stability, the Fe7S8/Fe2N NPs show outstanding OER and ORR electrocatalytic activities versus precious metal catalysts and pristine Fe2N nanoparticles. Prototype liquid and solid-state zinc-air batteries were also fabricated, and they both show significant rechargeable activities and cyclic stability.

La(OH)3-decorated NiFe nanoparticles as efficient catalyst for hydrogen evolution from hydrous hydrazine and hydrazine borane

Ultrafine NiFe nanoparticles (NPs) decorated by La(OH)3 have been successfully prepared via a facile one-step co-reduction method without the help of surfactant or support. It was found that after being decorated with La(OH)3, the NiFe–La(OH)3 NPs have a smaller particle size and lower crystallinity. The resultant NiFe–La(OH)3 nanocatalyst exhibits an excellent catalytic activity, 100% H2 selectivity, and satisfied recyclability for hydrogen evolution from hydrous hydrazine (N2H4·H2O) at 343 K under alkaline conditions, giving a high turnover frequency (TOF) value of 100.6 h−1, which is more than 35 times higher than pure NiFe NPs (2.8 h−1). The kinetics study shows that with respect to the concentration of catalyst and N2H4, the N2H4 dehydrogenation reaction follows fist-order kinetics and zero-order kinetics, respectively. Furthermore, NiFe–La(OH)3 also exhibits an outstanding performance and excellent recycle stability during high dehydrogenation of hydrazine borane (N2H4BH3). The excellent performances for the dehydrogenation of N2H4 and N2H4BH3 could be attributed to the strong interaction between La(OH)3 and NiFe NPs, as well as ultrafine and low crystalline NiFe NPs due to the addition of La(OH)3.

Tailored NiFe Catalyst on Silicon Photoanode for Efficient Photoelectrochemical Water Oxidation

The decoration of n-type silicon (n-Si) with bimetallic NiFe nanoparticles has been shown to be an effective approach in achieving efficient photoelectrochemical (PEC) water oxidation. However, the...

Enhancing effect of Fe-doping on the activity of nano Ni catalyst towards hydrogen evolution from NH3BH3

The synthesis of inexpensive and efficient catalysts is of practical need for hydrogen generation from ammonia borane. In this work, a series of N-doped carbon coating NiFe nanoparticles (NPs) anchored on graphene was prepared by thermal pyrolysis of (NiFe-LDH)/polydopamine hybrid. The incorporation of certain amount of Fe is effective for enhancing the catalytic activity of Ni. The doping of Fe into Ni effectively optimizes the electronic structures of Ni NPs. In addition, the introduction of graphene oxide increases the apparent catalytic activity of Ni1.2Fe0.8 NPs from TOF value of 4.41 to 23.25 min–1 at 298 K. The efficient activity of prepared catalysts is attributed to the synergistic effect between Ni and Fe atoms. The strategy used for this work offers a new idea for the synthesis of bimetallic nanoalloy and demonstrates the promising potential of NiFe NPs for industrial applications in energy and environmental fields.

Synthesis and Characterization of Fe-Mn and Fe-Ni Nanoparticles by co-Precipitation Method for Ferrofluid Applications

In this paper, oleic acid coated Fe3O4, Fe0.8Mn0.2Fe2O4 and Fe0.8Ni0.2Fe2O4 nanoparticles have been synthesized by co-precipitation technique for the preparation of ferrofluids and were characterized for their structural information using XRD technique. The nanoparticles were then dispersed in kerosene to get the Fe-Mn and Fe-Ni ferrofluid. The effect of Mn and Ni substitution on Fe3O4 was established. FTIR spectroscopy was used to investigate the presence of Fe-O bonding and other chemical substance adsorbed on the surface of the particles. Magnetic measurements were done using VSM and EPR spectroscopy technique at room temperature.

Ultra-Small Fe2N/N-CNTs as Efficient Bifunctional Catalysts for Rechargeable Zn-Air Batteries

Zinc-air batteries (ZABs) have been considered as promising next-generation batteries due to their natural abundance, flat discharge voltage and high theoretical specific energy density. However, the wide application of these ZABs is seriously hindered by the high cost and poor electrochemical stability of noble electrocatalysts. In this paper, we develop a facile method to prepare ultra-small iron-based nitride and nitrogen doped carbon nanotubes (Fe2N/N-CNTs) hybrid materials as bifunctional electrocatalysts for ZABs. In the presence of CNTs with large surface areas, ultra-small Fe2N nanoparticles with the diameter of around 5 nm are successfully prepared. The oxygen reduction reaction (ORR) activity of Fe2N/N-CNTs is comparable to the Pt/C, while the oxygen evolution reaction (OER) activity is much better than the Pt/C. At last, the home-made ZABs with Fe2N/N-CNTs have significant rechargeable activities and cyclic stability.