Gas-phase Reduction Research Articles

High stability of electrocatalytic hydrogen evolution from Ru-WC/NC 0D-2D nanocomposites

Pt based noble metal catalysts are important and efficient electrocatalysts during hydrogen evolution reaction (HER). However, the HER of Pt based noble metal catalysts have poor stability and high cost. Herein, Unique Ru loaded the tungsten carbide/nitrogen doped carbon (Ru-WC/NC) 0D-2D nanocomposites were fabricated by gas-phase reduction pyrolysis process to solve the problem of poor stability and high cost. Specifically, 0D WC-supported ultra-small Ru (∼2 nm) was anchored on nitrogen doped carbon nanosheets. Even with a remarkably low Ru loading of just 2.82 %, the developed catalyst achieves comparable high catalytic performance to that of a 20 % Pt/C catalyst and demonstrates superior stability. Under a current density of 10 mA cm−2, the Ru(2)-WC/NC catalyst shows an overpotential of 30 mV in acidic conditions and 51 mV in alkaline environments. Additionally, the overpotential of Ru(2)-WC/NC lower than that of commercially 20 % Pt/C at high current densities exceeding 50 mA cm−2. The total potential of water splitting for the two-electrode system comprising Ru(2)-WC/NC with commercial ruthenium oxide was 1.56 V at 10mA cm−2. Most importantly, the stability of Ru(2)-WC/NC is much better than that of Pt/C. Theoretical calculation results further revealed that the ΔGH* of Ru(2)-WC/NC catalyst could be reduced through synergistic interactions between Ru and WC, thereby optimizing the kinetics of HER. This study offers both theoretical insights and practical methodologies for the synthesis and evaluation of electrocatalysts modified with low loading of noble metals.

MPS@BWO with High Adsorption Capacity for Efficient Photocatalytic Reduction of CO2

Photocatalysis can reduce CO2 to available energy by means of light energy, which is considered to be an effective solution to alleviate energy and environmental problems. In this paper, an MPS@Bi2WO6 composite photocatalyst was prepared by in situ hydrothermal method. BWO grew on the surface of MPS, which increased the CO2 absorption capacity of the photocatalyst and improved the microstructure. Under the synergistic effect of the two aspects, BWS achieves the enhancement of light energy absorption capacity and can effectively excite electron-hole pairs. The transition electrons with high reduction ability migrate to the surface and contact with high concentrations of CO2, achieving efficient CO2 reduction under visible light. Among the photocatalysts in this paper, BWS-1 (BWO: MPS = 1:1) has efficient CO2 gas phase reduction ability under visible light, and the CO yield reaches 29.51 μmol/g. The MPS@BWO photocatalyst is a low-cost and efficient CO2 photoreduction catalyst with broad application prospects.

Fabrication of ultra-precise flexible electrothermal film by direct-write printing porous graphene-Ag structure

In this study, graphene oxide (GO)‑silver nitrate (AgNO3) composite ink was prepared with stable printability, which could match the direct-write print technique for patterning GO-AgNO3 composite structure. Reduced graphene oxide (rGO)‑silver (Ag) porous structure could be obtained with a freeze-drying and gas phase reduction process. The rGO-Ag porous structure could reach a conductivity of 3.2 × 105 S/m through quantum penetration effect with the bridging action. Subsequently, polydimethylsiloxane (PDMS) encapsulated the rGO-Ag porous structure, and a special composite structure of PDMS/ rGO-Ag/PDMS films could be obtained by adjusting the wetting effect. PDMS provided a good tensile property and excellent bending resistance, and then a relative resistance changes within 5 % could be achieved after the number of 10,000 bending times. With the rGO-Ag porous structure compressed into a thinner film, an ultra-precise flexible electrothermal performance could be realized with the conductive network and flexible package structure. The surface temperature of fabricated composite film could reach 201.3 °C at the voltage of 7 V, within a heating time of 25 s, and maintaining the temperature for 1800 s. Meanwhile, the flexible electrothermal film could keep a stable temperature after 120 power on/power off cycles. Furthermore, the flexible electrothermal film also has a linear temperature control ability, which could carry out the linear temperature control with different temperature regions. At last, the ultra-precise flexible electrothermal film exhibits an excellent applying effect for the wrist hot compress, pipeline heating and window cleaning with uneven ice thickness. Therefore, the direct-write printed porous graphene-Ag structure presents a special property for fabricating ultra-precise flexible electrothermal film, which could provide a great research significance and application value in printing electronic structure and manufacturing electronic device.

Reactive molecular dynamics simulations of lithium-ion battery electrolyte degradation

The development of reliable computational methods for novel battery materials has become essential due to the recently intensified research efforts on more sustainable energy storage materials. Here, we use a recently developed framework allowing to consistently incorporate quantum-mechanical activation barriers to classical molecular dynamics simulations to study the reductive solvent decomposition and formation of the solid electrolyte interphase for a graphite/carbonate electrolyte interface. We focus on deriving condensed-phase effective rates based on the elementary gas-phase reduction and decomposition energy barriers. After a short initial transient limited by the elementary barriers, we observe that the effective rate shows a transition to a kinetically slow regime influenced by the changing coordination environment and the ionic fluxes between the bulk electrolyte and the interface. We also discuss the impact of the decomposition on the ionic mobility. Thus, our work shows how elementary first-principles properties can be mechanistically leveraged to provide fundamental insights into electrochemical stability of battery electrolytes.

Synthesis of thin film infinite-layer nickelates by atomic hydrogen reduction: Clarifying the role of the capping layer

We present an integrated procedure for the synthesis of infinite-layer nickelates using molecular-beam epitaxy with gas-phase reduction by atomic hydrogen. We first discuss challenges in the growth and characterization of perovskite NdNiO3/SrTiO3, arising from post growth crack formation in stoichiometric films. We then detail a procedure for fully reducing NdNiO3 films to the infinite-layer phase, NdNiO2, using atomic hydrogen; the resulting films display excellent structural quality, smooth surfaces, and lower residual resistivities than films reduced by other methods. We utilize the in situ nature of this technique to investigate the role that SrTiO3 capping layers play in the reduction process, illustrating their importance in preventing the formation of secondary phases at the exposed nickelate surface. A comparative bulk- and surface-sensitive study indicates that the formation of a polycrystalline crust on the film surface serves to limit the reduction process.

Epitaxial growth of rare-earth yttrium on nanosheets to form semicoherent interface in zinc implant

Molybdenum disulfide (MoS2) nanosheet as nano reinforcement exhibits great advantages in zinc (Zn) implant due to its coordinated crystal slip and grain boundary strain effect. Nevertheless, the poor interface bonding restrains the coordination effect of MoS2. In this work, rare earth yttrium (Y) was used to epitaxial grow on the vacancy nucleation sites of MoS2 plane through a gas phase reduction method, and then introduced into Zn to improve their interface bonding. On one hand, rare earth Y could form a semicoherent interface with Zn due to the similar atomic arrangement and small lattice misfit between (101)Y plane (0.272 nm) and (002)Zn plane (0.248 nm). On the other hand, it could be tightly integrated together with sulfur element of MoS2 via covalent bond. As a result, the plastic strain of composites was improved from 6.1 % to 10.45 %. Simultaneously, the fracture energy was also increased to 201 × 103 J/m2, since rare earth Y considerably promoted load transfer efficiency from Zn matrix to MoS2 and thereby significantly activated slip systems. Encouragingly, the mechanical strength of the Zn-based biocomposite simultaneously reached 273.3 ± 10.9 MPa due to load transfer strengthening and grain refinement.

Effect of coke reactivity on reduction behaviours and non-isothermal kinetics of sinter at 1173–1373 K

ABSTRACT Utilizing high-reactivity coke is a critical approach for low-carbon iron-making. In this study, we investigated the effect of coke reactivity on reduction behavior and non-isothermal kinetics of sinter. The results show that the mass-loss rate of the burden gradually increased with increasing coke reactivity. At 1173-1373 K, the reduction process complied with the mechanism model F 2 of second-order chemical reaction control. The integral form of F 2 is G(α)=(1–α)-1–1, and the α is the extent of the conversion. The coke reactivity did not affect the reduction mechanism of the sinter. The apparent activation energy E of the reduction process without coke was 93.39 kJ/mol. As the coke CRI was 24.75%, 30.80%, 41.25%, and 45.11%, the E was 89.13 kJ/mol, 88.63 kJ/mol, 85.60 kJ/mol, and 77.27 kJ/mol, respectively. The gasification reaction of coke with high reactivity can enhance the gas-phase reduction ability of the reduction process.

Zn-Introduced Platinum-Cobalt Intermetallic Catalyst for Oxygen Reduction Reaction

Extensive commercialization of polymer electrolyte membrane fuel cells (PEMFCs) is restricted by high price of Pt which is commonly used to promote the oxygen reduction reaction (ORR). Therefore, reducing the dosage of Pt in the ORR catalysts while maintaining high activity and stability is important key for accelerating PEMFCs’ commercialization. In this study, Zn-introduced PtCo intermetallic nanoparticles supported on Zn-NC substrate (Zn-PtCo/Zn-NC) were synthesized, demonstrating superior activity and durability toward the acidic ORR in half-cell. The Zn-PtCo/Zn-NC catalyst was synthesized via the gas phase reduction method for the deposition of PtCo nanoparticles (NPs) on Zn-NC, and subsequent post-annealing process. During the annealing procedure, diffusion of Zn atoms into PtCo NPs occurred and leaded to enhanced atom-ordering of the intermetallic NPs. In the half-cell configuration, the Zn-PtCo/Zn-NC catalyst showed about 7.3-fold enhancement in the mass activity, compared to that of the commercial Pt/C catalyst. The high activity of the Zn-PtCo/Zn-NC was attributed to the incorporation of Zn atoms and the ordered structure which synergistically enhanced the ligand effects. In addition, the polarization curve of the Zn-PtCo/Zn-NC showed only a negative shift of 9 mV in a half-wave potential after the accelerated durability test (ADT), indicating the excellent stability of the catalyst. The robustness of the Zn-PtCo/Zn-NC was reinforced due to the thermodynamically stable structure of the atom-ordered intermetallic phase. The synthesis strategy presented in this work provides new pathway for developing the electrocatalysts applicable to the energy conversion devices.

Discovering a catholyte free design for gas phase electrocatalytic NO gas reduction to NH3 at room temperature

Nitric oxide (NOx) is one of the most contributors to the health risks associated with breathing in flue gases and it is crucial to eliminate this pollutant from the air when solid waste is burned. Electrochemical gas phase reduction of NO to NH3 is the promising method to mitigating the accumulation of NO gas pollutants and producing a valuable NH3 as a product at room temperature. In this investigation, for the first time, we designed a catholyte-free cell for gas phase electrochemical NO to NH3 conversion using K2[Ni(CN)4] coated carbon felt (CF) electrode as a electrocatalyst at room temperature. Herein, K2[Ni(CN)4] heterogeneous mediator transfers the electron between the NO gas molecule and electrode. The NO removal efficiency and NH3 formation were simultaneously monitored by using online gas phase FTIR spectroscopy. In the catholyte-free gas phase NORR process, the K2[Ni(CN)4]/CF electrode exhibits excellent NORR performance, with a high NH3 yield rate of 1128.9 µmol h−1 cm−2, an excellent 89.5 % NH3 faradaic efficiency at − 1 V vs quasi reference Ag and enhanced long term NORR durability. It is noteworthy that, this is the highest yield rate and faradaic efficiency of NH3 during gas phase NORR at room temperature. In addition, K2[Ni(CN)4]/CF electrocatalyst exhibits 99 % of NO removal efficiency with the formation of value-added product (NH3). Moreover, the proposed electrocatalyst shows excellent chemical, and morphological stability after long durability NORR operations. Furthermore, the detailed electrode-electrolyte free cell, NORR reduction mechanism was proposed. Present discovery provides great insights for sustainable NORR operations in real-site applications.

A Parametric Study of the Crystal Phases on Au/TiO2 Photocatalysts for CO2 Gas-Phase Reduction in the Presence of Water

Au/TiO2 photocatalysts were studied, characterized, and compared for CO2 photocatalytic gas-phase reduction. The impact of the nature of the TiO2 support was studied. It was shown that the surface area/porosity/TiO2 crystal phase/density of specific exposed facets and oxygen vacancies were the key factors determining CH4 productivity under solar-light activation. A 0.84 wt.% Au/TiO2 SG (Sol Gel) calcined at 400 °C exhibited the best performance, leading to a continuous mean CH4 production rate of 50 μmol.h−1.g−1 over 5 h, associated with an electronic selectivity of 85%. This high activity was mainly attributed to the large surface area and accessible microporous volume, high density of exposed TiO2 (101) anatase facets, and oxygen vacancies acting as reactive defects sites for CO2 adsorption/activation/dissociation and charge carrier transport.

Synthesis of mixed-phase sodium titanates and their activity in visible-light driven reduction of carbon dioxide

Herein, we reported the method of synthesis of sodium titanates using metal-ammonia solution and their photocatalytic activity for the gas-phase reduction of carbon dioxide under visible light. The results of physicochemical measurements showed that the obtained samples resemble multiphase systems containing Na2Ti4O9, Na4Ti5O12, and Na0.8Ti4O8 of cylindrical forms. They demonstrated perfect adsorption of visible light and improved activity in the investigated process.

Metalloradical complex Co-C˙Ph3 catalyzes the CO2 reduction in gas phase: a theoretical study.

Metal-stabilized radicals have been increasingly exploited in modern organic synthesis. Here, we theoretically designed a metalloradical complex Co-C˙Ph3 with the triplet characters through the transition metal cobalt (Co0) coordinating a triphenylmethyl radical. The potential catalytic role of this novel metalloradical in the CO2 reduction with H2/CH4 in the gas phase was explored via density functional theory (DFT) calculations. For the CO2 reduction reaction with H2, there are two possible pathways: one (path A) is the activation of CO2 by Co-C˙Ph3, followed by the hydrogenation of CO2. The other (path B) starts from the splitting of the H-H bond by Co-C˙Ph3, leading to the transition-metal hydride complex CoH-H, which can reduce CO2. DFT computations show that path B is more favorable than path A as their rate-determining free energy barriers are 18.3 and 27.2 kcal mol-1, respectively. However, for the reduction of CO2 by CH4 two different products, CH3COOH and HCOOCH3, can be generated following different reaction routes. Both routes begin with one CH4 molecule approaching the metalloradical Co-C˙Ph3 to form the intermediate CoH-CH3. This intermediate can evolve following two different pathways, depending on whether the H bonded to Co is transferred to the O (pathway PO) or the C (pathway PC) of CO2. Comparing their rate-determining steps, we identified that the PO route is more favorable for the reduction of CO2 by CH4 to CH3COOH with the reaction barrier 24.5 kcal mol-1. Thus, the present Co0-based metalloradical system represents a viable catalytic protocol that can contribute to the effective utilization of small molecules (H2 and CH4) to reduce CO2, and provides an alternative strategy for the exploration of CO2 conversion.

Adsorption and Photocatalytic Reduction of Carbon Dioxide on TiO2

The photocatalytic activity of TiO2 depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO2 in the gas-phase reduction of CO2 is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO2 and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO2 in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.

Coarse-grained reduced MoxTi1−xNb2O7+y anodes for high-rate lithium-ion batteries

High-volumetric-energy-density lithium-ion batteries require anode material with a suitable redox potential, a small surface area, and facile kinetics at both single-particle and electrode level. Here a family of coarse-grained molybdenum substituted titanium niobium oxides MoxTi1−xNb2O7+y (single crystals with 1~2 μm size) underwent hydrogen reduction treatment to improve electronic conduction was synthesized, which is able to stably deliver a capacity of 158.5 mAh g−1 at 6,000 mA g−1 (65.2 % retention with respect to its capacity at 100 mA g−1) and 175 mAh g−1 (73 % capacity retention over 500 cycles) at 2,000 mA g−1, respectively. Via careful in situ electrochemical characterizations, we identified the kinetic bottleneck that limits their high-rate applications to be mainly ohmic loss at the electrode level (which mostly concerns electron transport in the composite electrodes) rather than non-ohmic loss (which mostly concerns Li+ lattice diffusion within individual particles). Such a kinetic problem was efficiently relieved by simple treatments of Mo substitution and gas-phase reduction, which enable full cells with high electrode density, and high volumetric energy/power densities. Our work highlights the importance of diagnosis, so that modifications could be made specifically to improve full-cell performance.

Formation of boron-doped silicon wires and control of dopant concentration using zinc, SiCl4 and BCl3

We synthesized boron-doped silicon wires (whiskers) in a gas phase reduction reaction of SiCl4 with zinc vapor. BCl3 was introduced into the reactor as a boron source, and we varied the concentration ratio of B/Si in the gas phase. The formed wires had an electrical resistivity in the range of 10–3 to 101 Ω cm, depending on the ratio of BCl3 to SiCl4 in the gas phase. The ratio of B/Si in the silicon wires was not directly proportional to that in the gas phase, suggesting a non-linear incorporation process of dopant during the vapour-liquid-solid growth. Comparison of our data with published studies using gold catalysts to form doped semiconductor nanowires showed a lower incorporation efficiency of dopant atoms from the gas phase when using the zinc catalyst in vapour-liquid-solid growth.

Across the Board: Hyunjoo Lee on Electrochemical CO2 Reduction.

In this series of articles, the board members of ChemSusChem discuss recent research articles that they consider of exceptional quality and importance for sustainability. This entry features Prof. Hyunjoo Lee, who discusses catalytic CO2 conversion into valuable chemicals using gas-phase reduction and electrochemical reduction. She reveals how imminent demands for a more sustainable society might find solutions in electrochemically synthesized chemicals.

Photocatalytic Reduction of CO2 Over Me (Pt, Pd, Ni, Cu)/TiO2 Catalysts

A series of TiO2 photocatalysts loaded with various metals (Pt, Pd, Ni, and Cu) were prepared by using the wet impregnation method. Their physicochemical properties were studied by using XRD, BET, TPR-H2, FTIR and TPD-NH3/CO2 techniques. The photocatalytic activity of samples was investigated in the gas-phase reduction of carbon dioxide under continuous flow operation mode. Among all investigated catalysts, the Pt and Ni were the most active in terms of the formation rate of methanol. In general, the photocatalytic activity of modified TiO2 decreased with increasing metal loading and reaction time. The reversible deactivation of photocatalysts was associated with the covering of TiO2 surface by the reaction products.

In-situ DRIFT investigation of photocatalytic reduction and oxidation properties of SiO2@\u03b1-Fe2O3 core-shell decorated RGO nanocomposite

In this work, SiO2@α-Fe2O3 core-shell decorated RGO nanocomposites were prepared via a simple sol-gel method. The nanocomposites were prepared with different weight percentages (10, 30, and 50 wt %) of the SiO2@α-Fe2O3 core-shell on RGO, and the effects on the structural and optical properties were identified. The photocatalytic reduction and oxidation properties of the nanocomposites in the gas phase were assessed through the reduction of CO2 and oxidation of ethanol using in-situ diffuse-reflectance infrared fourier transform spectroscopy (DRIFT). The prepared nanocomposite with (30 wt %) of SiO2@α-Fe2O3 showed superior photocatalytic activity for the gas phase reduction of CO2 and oxidation of ethanol. Enhancement in the activity was also perceived when the light irradiation was coupled with thermal treatment. The DRIFT results for the nanocomposites indicate the active chemical conversion kinetics of the redox catalytic effect in the reduction of CO2 and oxidation of ethanol. Further, the evaluation of photoelectrochemical CO2 reduction performance of nanocomposites was acquired by linear sweep voltammetry (LSV), and the results showed a significant improvement in the onset-potential (–0.58 V) for the RGO (30 wt %)-SiO2@α-Fe2O3 nanocomposite.

Effect of Reduction of Pt–Sn/α-Al2O3 on Catalytic Dehydrogenation of Mixed-Paraffin Feed

The effect of the Pt–Sn/α-Al2O3 catalyst reduction method on dehydrogenation of mixed-light paraffins to olefins has been studied in this work. Pt–Sn/α-Al2O3 catalysts were prepared by two different methods: (a) liquid phase reduction with NaBH4 and (b) gas phase reduction with hydrogen. The catalytic performance of these two catalysts for dehydrogenation of paraffins was compared. Also, the synergy between the catalyst reduction method and mixed-paraffin feed (against individual paraffin feed) was studied. The catalysts were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. The individual and mixed-paraffin feed dehydrogenation experiments were carried out in a packed bed reactor fabricated from Inconel 600, operating at 600 °C and 10 psi pressure. The dehydrogenation products were analyzed using an online gas chromatograph (GC) with flame ionization detector (FID). The total paraffin conversion and olefin selectivity for individual paraffin feed (propane only and butane only) and mixed-paraffin feed were compared. The conversion of propane only feed was found to be 10.7% and 9.9%, with olefin selectivity of 499% and 490% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of butane only feed was found to be 24.4% and 23.3%, with olefin selectivity of 405% and 418% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of propane and butane during mixed-feed dehydrogenation was measured to be 21.4% and 30.6% for the NaBH4 reduced catalyst, and 17.2%, 22.4% for the hydrogen reduced catalyst, respectively. The olefin selectivity was 422% and 415% for NaBH4 and hydrogen reduced catalysts, respectively. The conversions of propane and butane for mixed-paraffin feed were found to be higher when compared with individual paraffin dehydrogenation. The thermogravimetric studies of used catalysts under oxygen atmosphere showed that the amount of coke deposited during mixed-paraffin feed is less compared with individual paraffin feed for both catalysts. The study showed NaBH4 as a simple and promising alternative reduction method for the synthesis of Pt–Sn/Al2O3 catalyst for paraffin dehydrogenation. Further, the studies revealed that mixed-paraffin feed dehydrogenation gave higher conversions without significantly affecting olefin selectivity.

Modification of photocatalytic property of BaTiO3 perovskite structure by Fe2O3 nanoparticles for CO2 reduction in gas phase.

In this work, perovskite structure of BaTiO3 was coupled with Fe2O3 in different molar ratios achieving the best photocatalytic performance of CO2 reduction in the presence of CH4 as reducing agent; both of them are main greenhouse gases. The photocatalysts were synthesized by facile hydrothermal method. The samples were characterized by XRD, FTIR, FESEM, EDX, UV-Vis DRS, and photoluminescence (PL) analyses. The BaTiO3 synthesized in this research showed a weak PL signal which is due to the intrinsic ferroelectric property as has been observed in previous reports. Compared to the pure BaTiO3 and Fe2O3, the heterojunctions exhibited enhanced photocatalytic activity. The maximum CO2 reduction under visible light irradiation was obtained to be 22% during 60min process time. The enhanced photocatalytic activity could be attributed to the increased optical absorption, the good separation, and immigration of photogenerated charge carriers that decreased the recombination rate of charge carriers in the n-n heterojunction.