Fe(III) grafted MoO3 nanorods for effective electrocatalytic fixation of atmospheric N2 to NH3

Electrocatalytic nitrogen reduction reaction (ENRR) offers a carbon-neutral process to fix nitrogen into ammonia, but its feasibility depends on the development of highly efficient electrocatalysts. Herein, we report that Fe ion grafted on MoO₃ nanorods synthesized by an impregnation technique can efficiently enhance the electron harvesting ability and the selectivity of H⁺ during the NRR process in neutral electrolyte. In 0.1 M Na₂SO₄ solution, the electrocatalyst exhibited a remarkable NRR activity with an NH₃ yield of 9.66 μg h^?1 mg^?1_cat and a Faradaic efficiency (FE) of 13.1%, far outperforming the ungrafted MnO₃. Density functional theory calculations revealed that the Fe sites are major activation centers along the alternating pathway.     

Base-assisted transfer hydrogenation of CO2 to formate with ammonia borane in water under mild conditions

The reduction of CO₂ into value-added chemicals is highly desired, especially when there is no catalyst and the water is used as a green solvent under mild reaction conditions. In this work, an effective process for the base-assisted transfer hydrogenation of CO₂ to formate with ammonia borane (BH₃NH₃) in water is demonstrated under mild conditions without any catalysts. Further research shows that CO₂ reacts with water and base to produce bicarbonate intermediate which can be easily reduced to formate by BH₃NH₃. The role of base is to capture CO₂ and move the unfavourable equilibrium of CO₂ reduction towards the formation of product. This new mechanism can also lead to achieve the reduction of commercial bicarbonate or carbonate to formate under the same conditions.     

Mo2C embedded on nitrogen-doped carbon toward electrocatalytic nitrogen reduction to ammonia under ambient conditions

Electrochemical nitrogen reduction reaction (e-NRR) is an attractive prospect for ammonia production under mild conditions using renewable energy. However, developing efficient and stable electrocatalysts for driving e-NRR remains a great challenge. Herein, inspired by the biological nitrogen fixation via active Mo-nitrogenase, molybdenum carbide on N-doped porous carbon (Mo₂C/NC) derived from Mo/Zn-ZIFs was developed for the first time, as an efficient e-NRR electrocatalyst under ambient conditions. In 0.1 M Na₂SO₄ electrolyte, the Mo₂C/NC catalyst achieved a maximum NH₃ yield rate of 70.6 μmol h^?1 g_cat.^?1 and a faradaic efficiency of 12.3% at ?0.2 V vs. RHE. Additionally, Mo₂C/NC displayed favorable electrochemical selectivity and durability during the longtime electrolysis, attributed to the structural and electrochemical stability of Mo₂C and ZIFs-derived carbon framework. This work provides new perspectives upon metal carbides and their compounds as catalysts for efficient e-NRR.     

Facile electrochemical fabrication of magnetic Fe3O4 for electrocatalytic synthesis of ammonia used for hydrogen storage application

Ammonia (NH₃) offers extensive applications in industrial production; moreover, it is a potential carrier for hydrogen energy and an eco-friendly fuel. Electrocatalytic synthesis of NH₃ has drawn increasing research attention, wherein an excellent electrocatalyst plays a vital role. Iron (Fe) oxide nanomaterials with their high activity and cost effectiveness of its raw material Fe, have received significant attention in electrocatalytic N₂ reduction reaction (NRR) to synthesize NH₃. This study reports a rapid and cost-effective electrochemical method for synthesizing magnetic Fe₃O₄ nanoparticles, achieving gram-level production under ambient conditions. The synthesized magnetic Fe₃O₄ nanoparticles as electrocatalyst for NRR, achieved excellent faradaic efficiency of 16.9% and an optimal NH₃ yield of 12.09 μg h^?1 mg^?1_cat. at ?0.15 V (versus the reversible hydrogen electrode (RHE)) in 0.1 M Na₂SO₄. Besides, density functional theory (DFT) calculations indicate that the N≡N bond was fully activated, and the NRR proceeds mainly along the alternating hydrogenation pathway.     

Pd nanoparticles anchoring to core-shell Fe3O4@SiO2-porous carbon catalysts for ammonia borane hydrolysis

A modified Stöber method is applied to synthesize the magnetic core-shell Fe₃O₄@SiO₂ particles, followed by compositing a series of porous glucose-derived carbon with ZnCl₂ as etchant. Then, ultrafine Pd nanoparticles (NPs) are successfully anchored to the resulting Fe₃O₄@SiO₂-PC composites with an in-situ reduction strategy. The particle sizes of Pd NPs are mainly centered in the range of 2.3–4.3 nm in the as-prepared Pd/Fe₃O₄@SiO₂-PC catalysts, owning a hierarchical porous structure with high specific surface area (S_BET = 626.0 m² g⁻¹) and large pore volume (V_p = 0.61 cm³ g⁻¹). Their catalytic behavior for the hydrogen generation from ammonia borane (AB) hydrolysis is investigated in details. The corresponding apparent activation energy is as low as 28.4 kJ mol⁻¹ and the reaction orders with AB and Pd concentrations are near zero and 1.10 under the present conditions, respectively. In addition, the magnetic catalysts, which could be easily separated out by a magnet, are still highly active even after nine runs, revealing their excellent reusability.     

Thermoelectric properties of P‐doped and V‐doped Fe2O3 for renewable energy conversion

The effect of P and V contents on the microstructure and thermoelectric properties of Fe_2‐xM_xO₃ (M: P and V; 0 ≤ x ≤ 0.01) is studied. Higher P and V contents result in increases of both the grain size and density, thus increasing the electrical conductivity. The absolute values of the Seebeck coefficients of the Fe_2‐xP_xO₃ and Fe_2‐xV_xO₃ increase with increasing P and V contents up to x = 0.0075 and 0.005, respectively, and then decrease with further increase of its concentration. The addition of a small amount of V (0.005) to Fe₂O₃ leads to a marked increase in both the electrical conductivity and Seebeck coefficient. This means that the introduction of a small amount of V is highly effective for improving the thermoelectric properties of Fe₂O₃. Copyright © 2013 John Wiley & Sons, Ltd.     

Fe2O3/spinel NiFe2O4 heterojunctions in-situ wrapped by one-dimensional porous carbon nanofibers for boosting oxygen evolution/reduction reactions

One-dimensional (1D) nanofiber structure of electrocatalyst has attracted increasing attention in oxygen evolution/reduction reactions (OER/ORR) owing to its unique structural properties. Here, MIL-53(Fe) and Ni(NO₃)₂·6H₂O are incorporated into the electrospun carbon nanofibers (CNFs) to prepare the nickel-iron spinel-based catalysts (Fe₂O₃/NiFe₂O₄@CNFs) with 1D and porous structure. The marked Fe₂O₃/NiFe₂O₄@CNFs-2 catalyst has a tube diameter of approximately 300 nm, a high surface area of 282.4 m² g^?1 and a hydrophilic surface (contact angle of 16.5°), which obtains a promising bifunctional activity with ΔE = 0.74 V (E_1/2 = 0.84 V (ORR) and E_j10 = 1.58 V (OER)) in alkaline media. Fe₂O₃/NiFe₂O₄@CNFs-2 has a higher catalytic stability (93.35%) than Pt/C (89.36%) for 30,000 s tests via an efficient 4e^? ORR pathway. For OER, Fe₂O₃/NiFe₂O₄@CNFs-2 obtains a low overpotential of 350 mV and a high Faraday efficiency of 92.7%. NiFe₂O₄ (Ni²⁺ in tetrahedral position) relies on its variable valence states (NiOOH and/or FeOOH) to obtain good catalytic activity and stability for OER, while CNFs wrap/protect the active components (Fe–N and graphic N) in the carbon skeleton to effectively improve the charge transfer (conductivity), activity and stability for ORR. Porous 1D nanofiber structure provides abundant smooth pathways for mass transfer. It indicates that the bimetallic active substances can promote bifunctional activity by synergistically changing the oxide/spinel interface structure.     

TiO2纳米管限域Fe2O3的可见光分解水制氢性能

通过真空−超声辅助的等体积浸渍法制备了TiO2纳米管限域Fe2O3催化剂,考察了其可见光分解水制氢性能。由于TiO2纳米管的限域效应,导致Fe2O3颗粒减小,分散度提高,能隙增大,光生载流子得到有效分离,提高了其光解水制氢活性。     

Self-doped Ti3+ mediated TiO2/In2O3/SWCNTs heterojunction composite under acidic/basic heat medium for boosting visible light induced H2 evolution

Well-designed Ti³⁺/In³⁺ mediated TiO₂/SWCNTs heterojunction composite for photocatalytic H₂ evolution under visible light has been investigated. The samples, fabricated through one-step sol-gel approach with controlled acidic/basic heat treatment environment, were characterized by XRD, Raman, FE-SEM, TEM, XPS, UV–Vis and PL techniques. The maximum H₂ of 1244 ppm h⁻¹ was evolved over In/SWCNTs/TiO₂, a 4.69, 1.54 and 1.53 times higher than using TiO₂, In/TiO₂ and SWCNTs/TiO₂ samples, respectively. This enhancement was due to faster charges separation and higher visible light absorption by synergistic effect of In/SWCNTs. Using catalyst prepared under basic (H₂) treatment, Ti³⁺ was successfully embedded into In⁺³@TiO₂@SWCNTs, exhibited H₂ production of 1446 ppm h⁻¹ which was 12.49% and 15.02% higher compared to catalysts prepared under CO₂ and N₂ atmospheres, respectively. Thus, surface defects like Ti³⁺ inhibits charges recombination and enables visible light responsive. The quantum yield over Ti³⁺/In³⁺ mediated TiO₂/SWCNTs composite was 0.251%, a 1.13 and 1.2 folds higher compared to CO₂ and N₂ atmospheres, respectively. Besides, excellent stability for H₂ generation was observed in cyclic runs. A possible mechanism is proposed to understand synergistic effects between Ti⁺³/In⁺³ in TiO₂/SWCNTs composite catalyst and has great potential as a green photocatalyst in environmental and energy applications.     

In-situ synthesis of TiO2/La2O2CO3/rGO composite under acidic/basic treatment with La3+/Ti3+ as mediators for boosting photocatalytic H2 evolution

Graphene-bridged, carbonate-coordinated and lanthanum modified TiO₂ nanocomposite (La/Ti³⁺/TiO₂/La₂O₂CO₃/rGO) was established using sol-gel assisted modified hydrothermal method followed by acidic/basic heat treatment. The synergistic effect of La/La₂O₂CO₃ in rGO bridged Ti⁺³/TiO₂ nanocomposite was investigated for dynamic H₂ production from ethylene glycerol-water mixture in a slurry phase continuous flow photoreactor system. La-TiO₂/rGO showed H₂ evolution rate of 462 μmol/h which was about 1.24, 1.51 and 5.13 folds higher compared to La/TiO₂, rGO/TiO₂ and pure TiO₂ samples, respectively. Furthermore, when La-TiO₂/rGO nanocomposite was treated under H₂/CO₂ atmosphere, a great potential in photocatalytic H₂ production with a rate of 583 μmol/h was obtained, which was ~1.02, 1.17 and 1.26 times higher than using H₂, CO₂ and N₂ atmospheres, respectively. This significantly enhanced productivity was due to formation of La₂O₂CO₃, increased absorptive properties of TiO₂ and changes in elemental level like Ti³⁺ state, which improves light absorption properties and producing more electrons with their hindered recombination rate by rGO. Specifically, existence of La₂O₂CO₃ could facilitate the basicity of catalyst and contributes in the decomposition of ethylene glycol for H₂ evolution. Next, apparent quantum yield of La-TiO₂/rGO calcined in CO₂/H₂ composite was 1.3 folds higher than using La-TiO₂/rGO composite. Moreover, the stability comparison reveals that CO₂/H₂ treated sample showed stability in cyclic runs due to better interactions of its components and formation of interface species like Ti³⁺ and La₂O₂CO₃. Therefore, fabrication of composite under well-controlled atmospheric heat treatment could be promising to develop graphene supported metal oxides with their unique structures towards visible light enhanced photocatalytic H₂ production applications.     

Activating Fe2O3 using K2CO3-containing ethanol solution for corn stalk chemical looping gasification to produce hydrogen

Alkaline organic liquid waste was introduced to activate Fe₂O₃ and provide sufficient steam to boost biomass chemical looping gasification (CLG) for H₂ production. Experiments under different excess oxygen ratios, temperatures, and alkali contents were performed to investigate the reaction characteristics of alkaline organic waste - biomass CLG. The highest H₂ yield of 1.71 L and carbon conversion rate of 83.8% were obtained at the excess oxygen ratio of 0.2, the alkali concentration of 6%, and the reaction temperature of 800 °C. Moreover, the kinetic and thermodynamic analysis under the optimized condition have cast light on the fundamental understanding of alkaline organic liquid waste - biomass CLG. Results demonstrate that this novel approach has the potential to enhance energy conversion.     

Creation of oxygen vacancies to activate Fe2O3 photoanode by simple solvothermal method for highly efficient photoelectrochemical water oxidation

Photoelectric chemical (PEC) decomposition of water is regarded as one of the most promising ways to convert solar energy into hydrogen energy, which has attracted extensive attention from researchers at home and abroad. Among the numerous photoanode materials, α-Fe₂O₃ is considered to be one of the most promising photocatalytic materials. However, due to the poor conductivity, short photogenerated charge life and high overpotential of water oxidation reaction, the development and application of α-Fe₂O₃ is seriously hindered. Recently, the introduction of oxygen vacancies is an effective method to improve the efficiency of α-Fe₂O₃ photoelectric conversion. In this work, oxygen vacancy was introduced in Fe₂O₃ photoanode by simple solvothermal method with ethylene glycol as solvent at 160 °C. The photoelectric catalytic activity of eg-Fe₂O₃ was significantly improved for solvothermal process. At 0.186 V_SCE (1.23 V_RHE), the photocurrent density of eg-Fe₂O₃ photoanode could reach 2.8 mA/cm², which is 1–2 orders of magnitude higher than that of pristine Fe₂O₃ photoanode (0.1 mA/cm²). XPS test results show that the solvothermal process with ethylene glycol at 160 °C introduces oxygen vacancy to Fe₂O₃ photoanode. The tests of electrochemical impedance spectroscopy and photoelectrochemical impedance spectroscopy indicate that the introduction of the oxygen vacancy significantly improve the conductivity of the Fe₂O₃ photoanode and reduces the resistance of charge transmission between the electrode catalytic material and the electrolyte, which are the main reasons for the improvement of photoelectric water oxidation activity. This work provides a new method for improving the photoelectrochemical water oxidation by iron oxide photoanode.     

Gd,La co-doped CeO2 as an active support for Fe2O3 to enhance hydrogen generation via chemical looping water gas shift

Support materials are indispensable to promote the durability of iron oxides for chemical looping applications. However, the dilution effect of supports on the active phase would lead to decreased bulk oxygen conduction, thus leading to compromised activity. Here, we propose several Gd³⁺, La³⁺ and Nd³⁺ doped CeO₂ as active supports for iron oxides and investigate the support effect to improve hydrogen generation via chemical looping water gas shift. The characterizations show that the dopants improve the oxygen vacancy concentration in the CeO₂ lattice and Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ exhibits the most oxygen vacancy concentration among all the oxygen carriers. Pulse reactions of oxygen carriers show that an abundance of oxygen vacancy concentration can promote the lattice oxygen transfer in bulk, thus contributing to improved redox reactions. The high oxygen conductivity mitigates the dilution effect on the active phase. Therefore, Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ shows the highest hydrogen yield (～9.49 mmol^?1.g^?1) and hydrogen generation rate (～0.632 mmol.g^?1.min^?1) with only a slight decrease at 650 °C over 100 cycles. Overall, this work highlights the influence of support properties on the redox reactivity of iron oxides for chemical looping applications.