Reductive Atmosphere Research Articles

Effects of pyrolysis temperature and atmosphere on grinding properties of semicoke prepared from Shenmu low-rank coal

This study investigated the effect of temperature and atmosphere on the grindability of the semicoke prepared via a mid–low temperature pyrolysis of low-rank Shenmu coal, analyzed the variation in its grinding characteristics with the increase of ball grinding duration, and explored the influence mechanism of the pyrolysis conditions on the grindability of semicoke based on the pyrolysis process and semicoke structure evolution. The results show that as the pyrolysis temperature increases (400–700 °C), grindability and grinding mechanism of the semicoke change significantly; the grindability first increases and then decreases with the increase of the pyrolysis temperature. As the grinding duration increased, high-Hardgrove grindability index (HGI) semicoke underwent intensive bulk grinding at a specific grinding time. Additionally, the varying contents of the proximate analysis during devolatilization are not the main cause of the varying HGI during pyrolysis. Using thermogravimetric and thermomechanical analyses, the optimal grindability of the semicoke was found to occur at the transition stage of the pyrolysis to pyrocondensation reactions (approximately 600 °C). During the transition, the intense pyrolysis reaction led the semicoke to have abundant pores and cracks, a highly disordered chemical structure, and low matrix hardness. The porous semicoke which has high grindability first underwent surface grinding; subsequently, the loose cores were more prone to bulk grinding, whereby the optimal grindability was obtained. HGIs of the semicoke prepared in the reductive atmospheres such as H2, CO and CH4 are lower than that of the semicoke prepared in N2 atmosphere at the same pyrolysis temperature. Moreover, the reductive atmospheres inhibited pore development in the semicoke and made its carbon structure more ordered, which densified the structure and decreased the grindability of the semicoke.

Oxygen‐Saturated Strong Metal‐Support Interactions Triggered by Water on Titania Supported Catalysts

AbstractStrong metal‐support interaction (SMSI) greatly improves the performances of various supported metal nanoparticle catalysts. Classical SMSI relies on the oxide species with substoichiometric oxygen concentration, which prefers to retreat off in humid and oxidative atmospheres. A SMSI is reported with oxygen‐saturated overlayers on Au/TiO2 catalyst achieved by steaming treatment, an opposite condition to the classical SMSI formation. Through a combination of experimental and theoretical methods, this study demonstrates that the strong interactions between the TiOxHy (x≥2) species and Au surface cause the support migration to encapsulate Au nanoparticles. The oxygen‐saturated oxide overlayers are stable in oxidative, reductive, and humid atmospheres, providing great vitality to stabilize metal nanoparticle catalysts under varied and complex reaction conditions to outperform the classical SMSI.

Effect of magnetite addition to ilmenite on hydrogen-rich reduction of its oxidized powder

In this study, the oxidation powder sample of ilmenite concentrate with 15% magnetite concentrate was prepared, and the subsequent isothermal reduction was investigated at temperatures in the range of 950–1050 °C with CO, H2, and their mixtures. The hydrogen-rich atmosphere, magnetite effect, apparent activation energy, and micromorphology of the reduced samples were investigated. The results indicated that the mass loss of the raw sample in the reduction process exhibited a similar tendency to that of the preoxidized ilmenite concentrate, although the addition of the magnetite concentrate increased the total mass loss. The influence of Fe2O3, which is produced by the oxidation of magnetite, on the mass-change ratio in the reduction process is separated and drawn novelty. The interaction between the magnetite and ilmenite concentrates in the oxidation process did not exhibit an apparent hindering effect following the hydrogen-rich reduction of the raw sample powder. The reducing atmosphere had a slight influence on the average apparent activation energy. The average apparent activation energies of the reduction of the raw sample were 55.34, 53.54, 52.78, 59.14, and 53.85 kJ/mol when the reducing atmosphere was CO, H2/CO = 0.4, H2/CO = 1, H2/CO = 2.5, and H2, respectively. Furthermore, the change in micromorphology of the reduced sample with the hydrogen-rich content in the reduction atmosphere is also discussed.

Effects of different atmosphere on reaction behaviors of metallised burden

ABSTRACT The utilisation of metallised burden in blast furnace (BF) as a way of CO2 emission reduction has been widely considered. One of the major concerns is its reoxidation by CO2 in the upper part of BFs. In this study, the non-isothermal reaction behaviours of metallised burden with a metallisation ratio of 70% in different CO2 + CO gas mixtures were analysed. The results showed that the metallised burden can be oxidised by CO2 under sufficiently large CO2 partial pressure. In a 50%CO2 + 50%CO gas mixture, Fe was oxidised to FeO. And the reaction started at 718°C, which is much higher than the temperature in the upper shaft of BFs. The metallised burden cannot be oxidised by CO2 in the low temperature zone of BFs. During the descent of the burden, temperature increases and the reduction atmosphere strengthens in an actual BF. The CO2 partial pressure is insufficient to oxidise the metallised burden.

The Search of Artistic Surface Effects of Metal Waste Additive Ceramic Material in Reductive Firing Atmosphere

Nüfusu giderek artan dünyada insan, ilk keşif zamanlardan bugüne ihtiyaçları doğrultusunda yaşam koşulları iyileştirmek amacıyla özellikle teknolojik açıdan oldukça önemli bir yol katetmiştir. Üretimin arttığı dünyada, doğru orantılı olarak tüketim de artmış ve zamanla gelişen aşırı tüketim eğilimi, üretim- tüketim dengesizliğine, dolayısıyla kontrolsüz atık oluşumuna sebebiyet vermiştir. Üretim ve tüketim fazlası organik ve inorganik atıkların dönüştürülememesi durumunda çevreye verdiği tahribattan dolayı sanat da dahil bir çok farklı alanda geri dönüşüm projeleri önem kazanmıştır. 
 Seramik üretim sanayinin atığı olan ıskartaya çıkarılan seramik malzeme, sanatçılar tarafından çeşitli yöntemlerle değerlendirilirken, farklı organik ve inorganik atıklar da gerek seramik sanatında sanat medyumu olarak gerekse seramik kimyasında hammadde olarak kullanılmaktadır. Bu bağlamda, bir kil çeşidi olan stoneware bünye ile çeşitli metal üretim atölyelerindeki atık metallerin sırda kullanılan metal oksitlere alternatif bir seçenek olarak kullanım olanaklarının araştırılması hedeflenmiştir. Araştırma sahası olarak İzmit ve Sakarya illerindeki metal üretimi yapan işletmeler araştırılmış ve atık malzeme desteği sağlanmıştır. Üretim atığının sürekli ve düzenli olduğu işletmelerdeki atık metallerin numulerinin üniversite laboratuvarında ön çalışması yapılmıştır. Atık malzemeler ile seramiği farklı yöntemlerle bir arada kullanan ve özellikle çamur içerisine inorganik katkıları ekleyerek çalışan sanatçıların teknikleri incelenmiştir. Bugüne kadar yapılan çalışmalardan farklı olarak ise, seçilen atık metallerin, seramik hammaddelerinden metal oksitlerin yerini metal atıklarının alıp alamayacağı tartışılmıştır.
 Sırda renk veren metal oksitlerin redüktif pişirim atmosferinde renk değiştirdiği bilgisinden hareketle, seçilen çelik, alüminyum, bakır ve demir atıkları için de aynı denemenin yapılması planlanmıştır. Böylece geri dönüşüm projesi kapsamında, atık metallerin renklendirici oksit yerine hammadde olarak seramik sanatında kullanımı, tek bir metal atık ile birden fazla alternatif yüzey etkileri elde etmek mümkün olmuştur.

3D hierarchical porous structures printed from a silica-nickel composite paste

Material extrusion of paste as one of the 3D printing techniques is commonly used in additive manufacturing industry. It allows to efficiently obtain structures of complex geometry at a relatively low cost. Ceramics are among the materials eagerly printed with this technique, especially as a support material. Hence, the combination of silica as base material and nickel as catalyst seems to be a highly promising system in processes such as CO2 methanation or hydrogenation processes.The key aspects that should be taken into consideration when designing a new material are the proper material composition, its microstructure, as well as the final properties. From the point of view of the above-mentioned applications, material should have high open porosity. Appropriate micro- and macroporosity enable the optimal flow of liquid and gaseous reagents through the material, ensuring high efficiency of the processes carried out. It is also crucial to select the appropriate catalytic material, hence the use of nickel as a catalytically active metal was proposed for the research.This article demonstrates the development, preparation and characterization of silica-nickel porous structures obtained via material extrusion. The nanosilica-Ni paste with 75 wt% of Ni powder particles was prepared with stirring and degassing for homogenous consistency. 3D printed scaffolds have undergone heat treatment to remove the organic binders and partially sintered to achieve a relevant mechanical strength. The analysis of the paste was performed using the detailed thermal analysis, XRD analysis and Raman spectroscopy for a determination of the optimal thermal processing conditions. In addition, the characterization of the final materials was carried out to confirm the effectiveness of the procedures developed. Application of the reductive atmosphere (mixture of N2+H2) during heat treatment prevented nickel particles from oxidation, as well as strongly eliminated the microstructure defects such as cracking and material shrinkage. The results demonstrate the perspective application of material extrusion as a printing technique of highly porous materials with well-preserved pre-designed 3D geometry.

Defect evolution and effect on structure and electric properties of A/B site Sm doped BaTiO3 sintered in different atmospheres

BaTiO3 ceramics doped with different contents of Sm (0.5-7 mol%) are prepared by a homogeneous precipitation method and sintered in air (A-xSm) and reducing (R-xSm) atmosphere respectively. With the increase of doping amount, the phase structure of Sm-doped BaTiO3 ceramics gradually changes from tetragonal phase to cubic phase, and the cubic phase is stronger in R-xSm. In the air atmosphere, Sm ions preferentially replace Ba sites as donors at low doping concentration, which is easy to convert Ti4+ ions into Ti3+ ions, resulting high dielectric constant (>104) and semiconductor like properties. As the doping amount increases, Sm ions start to replace Ti sites as acceptors to generate oxygen vacancies, which capture the electrons generated by donor doping, thus decreasing the percentage of Ti3+ ions. As a result, the dielectric loss and permittivity are decreased, and the electrical insulation properties of A-xSm ceramics are gradually improved. However, in the reducing atmosphere, oxygen atoms in the lattice are easy to escape, resulting in many oxygen vacancies and free electrons. The increase of oxygen vacancy inhibits the substitution of Sm ion to Ti site, and the free electron leads to the increase the percentage of Ti3+ ions and R-xSm ceramics exhibit semiconductor like properties. Thermally stimulated depolarization currents (TSDC) testing verified that oxygen vacancies of A-xSm ceramics mainly capture space charges, and a small part of oxygen vacancies form defective dipoles [2SmTi′−VO..]. The complex impedance test shows that the change of resistivity of A-xSm ceramics is mainly closed to the influence of Sm doping on the grain not grain boundary of BaTiO3 ceramic.

Exsolution of Iron Nanoparticles from LCTFeO3 for Oxygen Evolution Reaction

Perovskite oxides (ABO3) with stable structures and flexible compositions are considered to be alternative catalysts for the oxygen evolution reaction (OER). With A-site deficiency in a perovskite, the doping metals in the B-site may be exsolved by calcination in a reduction atmosphere, which is a promising approach to increasing the activity of the catalyst. Here, an iron doped La(0.2+x)Ca(0.7-x)Ti(1-x)FexO3 (x = 0.05, 0.3, LCTFex) perovskite is successfully synthesized by a mild sol-gel method, and the iron nanoparticles anchored perovskite (R-LCTFex) can be fabricated after reduction under 5% H2/N2 atmosphere in a tubular furnace, which can be seen clearly in SEM and STEM images. Notably, the onset overpotential of R-LCTFe0.3 is reduced by 130 mV compared with LCTFe0.3 and the current density of R-LCTFe0.3 is 12-fold higher than LCTFe0.3 at the overpotential of 530 mV. The enhanced OER performance is triggered by the exsolution of Fe nanoparticles. This study establishes that exsolution of metal nanoparticles from a perovskite is a useful tactic for enhancing OER performance.

Solid Precipitation Behaviors in Coal Slag from Different Primary Phases and Their Effects on Slag Viscosity from Thermochemistry and Experimental

Undesired solid precipitation in coal slag at high temperatures can cause serious blockages, or even the shutdown of coal gasifiers, due to a rapid increase in slag viscosity. In this study, the solid precipitation behaviors of coal slag from different primary phases and under different atmospheres were both experimentally and theoretically investigated. Our results demonstrated that the viscosity of the coal slag in the primary phase of mullite was strongly influenced by the atmosphere at a typical tapping temperature of 1300 °C because of the high content of network formers. The viscosity of the partially crystallized slag was significantly affected by solid precipitation behavior. Iron was converted to magnetite and hematite in air and was reduced to metallic iron under a reducing atmosphere. Increasing CaO content improved both the iron reduction reaction and the slag crystallization behavior. Anorthite precipitation was largely inhibited under a mild reducing atmosphere, leading to a large difference in the viscosity of coal slag under different atmospheres. In contrast, the viscosity of the coal slag in the primary phase of mullite was slightly influenced by the atmosphere due to the weak crystallization tendency of mullite, as well as its high slag viscosity.

The effect of preheating temperature and combustion temperature on the formation characteristics of PM0.4 from preheating combustion of high-alkali lignite

Preheating combustion is getting popular because it can reduce NOx formation, but its effect on particulate matter (PM) formation is still unclear. This study focuses on the effect of preheating temperature (Tp) and combustion temperature (Tc) on the formation characteristics of fine mode particles (PM0.4) in preheating combustion. The mass-based particle size distribution, elemental compositions and morphologies of PM and number-based particle size distribution were analyzed to reveal the mechanisms of reducing PM0.4 formation during preheating combustion. The results showed that compared with conventional combustion, preheating combustion with optimized Tp and Tc can effectively decrease the mass yield of PM0.4 and NOx concentration by 77.9% − 82.2% and 70.9% − 77.8%, respectively. In preheating combustion, the mass yield of PM0.4 basically didn’t change with Tp. When Tc was lower than Tp, the mass yield of PM0.4 was basically unchanged with Tc. The precursors of PM0.4 mainly vaporized in the preheating furnace. The vaporization of inorganic elements, gas-to-particle transformation, and coagulation occurring in the combustion furnace had a negligible effect on the mass yield of PM0.4. When Tc was higher than Tp, increasing Tc can significantly increase the vaporization of inorganic elements from unburned char/coal particles in the combustion furnace. As a result, the mass yield of PM0.4 increased. To effectively reduce the formation of PM0.4 and NOx, a higher Tp and a lower Tc is suggested. The volatility of inorganic elements in preheating combustion has an order as S > Na > Mg > Fe≈Ca > Si. Refractory elements including Fe, Mg, and Ca contributed the most to decrease of PM0.4 in preheating combustion compared with conventional combustion. Preheating combustion has a stronger reductive atmosphere and a lower particle temperature. The vaporization of inorganic elements from coal particles in preheating combustion is probably determined by particle temperature rather than reductive atmosphere.

N, P co-doped Ni/Mo-based multicomponent electrocatalysts in situ decorated on Ni foam for overall water splitting

Developing the robust non-precious metal bifunctional electrocatalyst is highly imperative for the hydrogen evolution from overall water splitting. Herein, a Ni foam (NF)-supported ternary Ni/Mo bimetallic complex (Ni/Mo-TEC@NF), hierarchically constructed by coupling the in-situ formed MoNi4 alloys and Ni2Mo3O8 with Ni3Mo3C on NF, has been developed through a facile method involving the in-situ hydrothermal growth of the Ni-Mo oxides/polydopamine (NiMoOx/PDA) complex on NF and a subsequent annealing in a reduction atmosphere. Synchronously, N and P atoms are co-doped into Ni/Mo-TEC during the annealing procedure using phosphomolybdic acid and PDA raw materials as P and N sources, respectively. The resultant N, P-Ni/Mo-TEC@NF shows outstanding electrocatalytic activities and tremendous stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), due to the multiple heterojunction effect-promoted electron transfer, the large number of exposed active sites, and the modulated electronic structure by the N and P co-doping. It only needs a low overpotential of 22 mV to afford the current density of 10 mA·cm−2 for HER in alkaline electrolyte. More importantly, as the anode and cathode, it requires only 1.59 and 1.65 V to achieve 50 and 100 mA·cm−2 for overall water splitting, respectively, comparable to the benchmark Pt/C@NF//RuO2@NF couple. This work could spur the search for economical and efficient electrodes by in situ constructing multiple bimetallic components on 3D conductive substrates for practical hydrogen generation.

Transformation of Nd3+ Centers in Y2SiO5 Crystals during Heat Treatment in a Reducing Atmosphere and Gamma Irradiation

Transformation of Nd3+ Centers in Y2SiO5 Crystals during Heat Treatment in a Reducing Atmosphere and Gamma Irradiation

Polymorphic Cobalt Sulfide-Embedded Graphene Foam with Ultralong Cycling and Ultrafast Rate Capability for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) attract growing attention due to their low price and abundant resources. However, the main drawback is the large-sized potassium ions, which results in a lack of superior capacity and desirable stable materials. We herein propose the Co9S8/GF nanocomposite synthesized by a solvothermal route followed by heat treatment under the reduction atmosphere with the CoS/GF nanocomposite as the control group. The as-synthesized Co9S8 has a typical morphology of vertically arranged uniform nanosheet arrays. The Co9S8/GF nanocomposite electrode delivers a capacity of 345.65 mAh·g–1 after 600 cycles at 500 mA·g–1 and even 343.06 mAh·g–1 after 1360 cycles at 5000 mA·g–1 in KIBs. Besides, the discharge capacity can reach 461.05 mAh·g–1 after the current increases to 5000 mA·g–1 and a reversible capacity of 578.40 mAh·g–1 when the current density recovers to 250 mA·g–1 again. At last, the charge storage behaviors are mainly discussed, and the unique structure can suffer the volumetric change, especially at high current density, which opens up a novel and effective way to build the embedded porous structure for the next-generation KIB technology.

Effect of grains and grain boundaries on concentrations and mobility of charge carriers in Ba3Ca1.18Nb1.82O9-δ

Perovskite-based protonic conductors are currently the most promising electrolytes in medium and low-temperature hydrogen energy devices. Herein, the Ba3Ca1.18Nb1.82O9-δ double perovskite oxide protonic conductor is prepared, and the influence of bulk and grain boundaries on transport properties is systematically investigated via defect chemistry. The Ba3Ca1.18Nb1.82O9-δ exhibits a hexagonal distortion, and the calculated standard molar hydration enthalpies of Ba3Ca1.18Nb1.82O9-δ, bulk, and grain boundaries are -138 kJ/mol, -131 kJ/mol, and -144 kJ/mol, respectively. The migration activation energies of protons, oxygen vacancies, and hole conduction in bulk Ba3Ca1.18Nb1.82O9-δ under oxygen are 0.29 eV, 1.51 eV, and 0.63 eV, respectively. The proton concentration in grains is slightly lower than in grain boundaries. In contrast, the proton mobility in bulk is three orders higher than in grain boundaries. The proton conduction of double perovskite oxide protonic conductor is dominant in Ar and reductive atmospheres at 500–800°C, where the conductivity (σh·) and holes transport number (th·) increase with oxygen partial pressure. Therefore, the conduction of Ba3Ca1.18Nb1.82O9-δ could be enhanced by improving carriers’ mobility in grain boundaries. The right grain boundaries block oxygen vacancies at low temperatures, increasing the predominance area diagrams for proton conduction. Hence, grain boundaries control the transport property of double perovskite oxide protonic conductor.

Proton conductivity in Yb-doped BaZrO3-based thin film prepared by pulsed laser deposition

For increasing the performance of PCFC (Protonic Ceramic Fuel Cells), it is important to prepare high-quality thin films of electrolyte materials. In this study, the preparation condition of the thin film of BaZr0.8Yb0.2O2.9 (BZYb) by pulsed laser deposition (PLD) method was optimized and the electrical conductivities of the obtained films were measured. The thin film was prepared by PLD using two kinds of BZYb targets, which were prepared by solids state reaction and Pechini method. Both thin-film samples have the single phase of the cubic perovskite-type structure, however, morphology as well as the orientation of the BZYb film was significantly different. The thin film using the target material by Pechini method is a high crystalline orientation and partially oriented [211] direction. The electrical conductivities of the obtained thin films at reduction atmosphere are dominated by proton conductivity, which is almost the same as that of the bulk sample despite [211] orientation.

Electrochemical performances of LiNiCoMn bifunctional electrode for low temperature solid oxide fuel cells

Lithium transition metal oxides LiNi0.83Co0.11Mn0.06O2 (NCM-83) and LiNi0.8Co0.1Mn0.1O2 (NCM-811) are prepared and acted as cathodes and bifunctional electrodes for low temperature solid oxide fuel cells with H2 and CH4 fuels. The Ni anode-supported cell with NCM-83 cathode exhibits maximum power density (Pmax) of 0.72 W cm−2 with H2 fuel at 600 °C. The symmetric cell with NCM-83 electrodes shows high Pmax of 0.465 W cm−2 with H2 fuel and 0.354 W cm−2 with CH4 fuel at 600 °C. And the Pmax of the cell with NCM-811 as anode and NCM-83 as cathode is 0.204W cm−2 with H2 fuel at 600 °C. The oxygen vacancies in NCM materials are conducive to the rapid oxygen ion conduction of the cathode, and in the anodic reduction atmosphere, the NCM materials will generate Ni/Co active particles in situ, proving the NCM materials can be advanced bifunctional electrode materials for hydrogen oxidation reaction and oxygen reduction reaction at low temperature.

New ( αβγ )-incommensurate magnetic phase discovered in the MnCr2O4 spinel at low temperatures

The nuclear and magnetic structure of the spinel $\mathrm{Mn}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ is reinvestigated by magnetization, specific heat, and neutron diffraction experiments at different temperatures. Four samples of this spinel synthesized under different atmospheres are analyzed. Through these experiments, a new magnetic phase, with propagation vector ${\stackrel{P\vec}{k}}_{\mathrm{I}2}=(0.6597(1)\phantom{\rule{0.16em}{0ex}}0.5999(1)\phantom{\rule{0.16em}{0ex}}0.1996(2))$, not previously reported, is identified below 18 K when the sample is synthesized under a reductive atmosphere. A possible explanation for the different magnetic ground states observed is given based on the competition among the main exchange interactions present in the system. Using the magnetic superspace group formalism, the symmetry of the nuclear and magnetic structures is determined. The presence of transverse conical magnetic structures in the lower-temperature phases allows for multiferroicity in this compound, and the electric polarization direction is determined for each magnetic phase.

Color‐Tunable Eu3+, Eu2+‐Activated CaSiO3 Nano Phosphor Extract from Agricultural‐Recycling‐Food‐Waste Materials for Display Applications

A series of Eu3+ and Eu2+ doped wollastonite is produced with a modified sol–gel technique using agricultural‐food waste materials. Rice husk ash (RHA) and eggshell (ES) are used as an usher for silica and calcium oxide, appropriately, at different concentrations (0.0, 0.2, 0.4, 0.6, 0.8, and 1 mol%). Most investigations have documented photoluminescence (PL) from Eu3+ ions caused by electronic transitions between 4f levels (5D0 → 7FJ) but there is limited information on emissions from Eu2+ ions. Fourier transform infrared (FTIR) spectra and X‐ray diffraction (XRD) studies reveal that varying amounts of europium ions do not have any effect on the structure of the host. PL spectra display that europium ions exist in both trivalent and divalent forms. A valence change from Eu3+ to Eu2+ ion is investigated using luminescence measurements. As‐prepared Eu3+ activated β‐wollastonite emitted as red and reduction atmosphere using argon gas produced Eu2+ activated phosphor gives off blue light. X‐Ray photoelectron spectroscopy reveals that throughout the processing of the samples, Eu3+ cations are partially reduced to Eu2+ cations in argon gas atmosphere. These findings prove the feasibility of fabricating white light‐emitting diodes (white‐LEDs) for three‐band type (RGB) phosphors utilizing only one host crystal.

Overcoming the ultra-high C-rate limitation of LiFeBO3 with careful optimization of carbothermal synthesis conditions

Carbon coating with sucrose as the precursor under a moderate synthesis temperature of 500 °C results in a high-purity monoclinic LiFeBO3 phase. This material has a high specific discharge capacity of 200 mAh/g at 0.02 C, which is close to its theoretical capacity. However, its poor performance at high C-rates limits its utility in electric vehicles. Achieving ultra-high C-rate capability of more than 5 C for LiFeBO3 cathode for lithium-ion batteries is uncommon. To overcome this challenge, this study carefully optimizes the synthesis conditions, such as temperature and reducing atmosphere. In this work we utilize carbothermal synthesis method for modulating the reducing conditions. Usually, the carbothermal reaction is carried out using carbon at high temperatures which leads to the formation of CO and CO2 gases. In our work, we have utilized a mixture of sucrose and oxalic acid as the carbon source, that is intimately mixed with the other precursors to create moderate reducing conditions. Oxalic acid decomposes to generate CO which helps to attain the limited reducing atmosphere condition necessary to retain the low valence state of iron. This is important because the low valence state of iron is essential for a good rate-performance. However, if the amount of carbon source is too low, it can lead to poor rate-performance. On the other hand, if the amount of carbon source is too high, it can generate impurity phases, which can be detrimental to the material’s properties. The optimized sample can deliver electrochemical activity at ultra-high C-rates, even up to 30 C, which is achieved for the first time in this material. Comprehensive spectroscopic analyses reveal that multitude of factors, including improved particle crystallinity and better graphitization, favor the retention of the monoclinic phase during electrochemical cycling. A stable specific discharge capacity of 104 mAh/g at 10 C sets it as a benchmark for this material.

Hydrogen-Rich Pyrolysis from Ni-Fe Heterometallic Schiff Base Centrosymmetric Cluster Facilitates NiFe Alloy for Efficient OER Electrocatalysts.

Binary metal nickel-iron alloys have been proven to have great potential in oxygen evolution reaction (OER) electrocatalysis, but there are still certain challenges in how to construct more efficient nickel-iron alloy electrocatalysts and maximize their own advantages. In this work, a heterometallic nickel-iron cluster (L=C64 H66 Fe4 N8 Ni2 O19 ) of Schiff base (LH3 =2-amino-1,3-propanediol salicylaldehyde) is designed as a precursor to explore its behavior in the pyrolysis process under inert atmosphere. The combination of TG-MS, morphology, and X-ray characterization techniques shows that the Schiff base ligands in the heterometallic clusters produces a strong reductive atmosphere during pyrolysis, which enable the two 3d metals Ni and Fe to form NiFe alloys. Moreover, Fe2 O3 /Fe0.64 Ni0.36 @Cs carbon nanomaterials are formed, in which Fe2 O3 /Fe0.64 Ni0.36 is the potential active material for OER. It is also found that the centrosymmetric structure of the heterometallic Schiff base precursor is potentially related to the formation of the Fe2 O3 /Fe0.64 Ni0.36 alloy@carbon structures. The Fe2 O3 /Fe0.64 Ni0.36 @C-800 provides 274mV overpotential in 1m KOH solution at 10mAcm-2 in OER. This work provides an effective basis for further research on Schiff base bimetallic doping-derived carbon nanomaterials as excellent OER electrocatalysts.