High-temperature Thermal Reduction Research Articles

Thermally-driven adsorption/desorption cycle for oxygen pumping in thermochemical fuel production

The two-step cycle for solar-thermochemical fuels production and thermochemical energy storage benefits from low oxygen partial pressure in the high-temperature thermal reduction step. To be practical, low oxygen partial pressures must be reached by energetically efficient and economically affordable methods—a challenge currently not met by either mechanical vacuum pumping or by inert gas sweeping. To address this challenge, we have examined a promising, thermally-driven surface adsorption/desorption approach. Providing that appropriately designed materials can be identified as expected, this approach would substantially advance solar-thermochemical fuel production (water and carbon dioxide splitting), thermochemical energy storage, and related technologies.

Hybrids of Nickel-histidine Functionalized Graphene Quantum Dots: Fabrication and Non-enzymatic Glucose Sensing

In this work, a method of in-situ recombination of Ni2+ with histidine functionalized graphene quantum dots (His-GQDs) was constructed a three-dimensional network porous structure. The collected precipitate complex precursor was oxidized and the NiO-His-GODs were obtained. The NiO-His-GQDs compound was subjected to high-temperature thermal reduction by inert gas to form Ni-His-GQDs. On the one hand, the intimate contact between Ni nanoparticles and His-GQD greatly shortens the gap between the two complexes, resulting in faster electron migration speed; On the other hand, the conductive (Ni)/semiconductor (His-GQDs) catalytic interface can produce Stokes diode-like structures, accelerate the migration rate of holes carriers in the semiconductor, and exhibit good electrocatalytic activity. A Ni-His-GQDs modified electrode as non-enzymatic glucose electrochemical sensor was shown good electrocatalytic activity and anti-interference property. The concentration of glucose was detected by amperometric analysis, and showed a good linear relation in the concentration range of 5.0 × 10-6∼2.0 × 10-3 M. The detection limit (S/N = 3) is 1.7 × 10−6 M. In addition, interference of sodium chloride (NaCl), uric acid (UA), dopamine (DA) and ascorbic acid (AA) was less than 5.0 % in the same conditions indicating that the hybrids modified electrode sensor could be used for the sensitive and selective detection of glucose.

Preparation of graphene/W18O49 nanorod composites and their application in electrochromic performance

Reduced graphene oxide/W18O49 nanorod (rGO–WNd) composites are prepared through the high-temperature thermal reduction of ammonium tungstate and graphene oxide (GO). In the as-prepared rGO–WNd, W18O49 nanorods (WNd) exhibit better crystallinity and more stable properties than conventional W18O49 nanowires obtained using the solvothermal method. X-ray diffraction and Raman spectra confirm the coexistence of WNd and reduced GO (rGO). The cycle stability, capacitance, and electrochromic properties of the rGO–WNd composite film exhibit significant improvement compared with those of the pure WNd film. The rGO–WNd composite film achieves the best coloration efficiency at 535 nm. Studies have shown that the diffusion of ions is promoted and the charge transfer is accelerated after adding rGO. These conditions accelerate response time.

Single-Atom Catalysis toward Efficient CO2 Conversion to CO and Formate Products.

Simply yet powerfully, single-atom catalysts (SACs) with atomically dispersed metal active centers on supports have received a growing interest in a wide range of catalytic reactions. As a specific example, SACs have exhibited distinctive performances in CO2 chemical conversions. The unique structures of SACs are appealing for adsorptive activation of CO2 molecules, transfer of intermediates from support to active metal sites, and production of desirable products in CO2 conversion. In this Account, we have exemplified our recent endeavors in the development of SACs toward CO2 conversions in thermal catalysis and electrocatalysis. In terms of the support not only stabilizing but also working collaboratively with the single active sites, the proper choice of support is of great importance for its stability, activity, and selectivity in single-atom catalysis. Three distinctive strategies for SAC architectures-lattice-matched oxide supported, heteroatom-doped carbon anchored, and mimetic ligand chelated-are intensively discussed from the perspective of support design for SACs in different reaction environments. To achieve a high-temperature thermal reduction of CO2 to CO, TiO2 (rutile), lattice-matched to the IrO2 active site, was chosen as a support to realize the thermal stability of Ir1/TiO2 SAC, and it shows great capability toward CO2 conversion and excellent selectivity to CO due to the effective block of the over-reduction of CO2 to methane over single Ir active sites. In the electrochemical reduction of CO2 at low temperature, sulfur co-doped N-graphene was developed to achieve unique d9-Ni single atoms on the conductive graphene support, by which not only were the atomic Ni active sites trapped into the matrix of graphene for its stabilization, but also the modulation of electronic configuration of mononuclear Ni centers promoted the CO2 activation through facile electron transfer with an improved electroreduction activity. Inspired by the Ir mononuclear homogeneous catalysts in CO2 hydrogenation to formate, porous organic polymers (POPs) functionalized with a reticular aminopyridine group were purposely fabricated to mimic the homogeneous ligand environment for chelating the Ir single-atom active center, and this quasi-homogeneous Ir1/POP catalyst manifests high efficiency for hydrogenation of CO2 to formate under mild conditions in the liquid phase. Such SACs are of paramount importance for the transformation of CO2, with their coordination environment helping in the activation of CO2. Since the energy barrier for the dissociation of the second C-O bond of CO2 on single-atom sites is very high, these catalysts can give high selectivities toward CO or formate products. Thanks to SACs, the conversion of CO2 has become much easier in various chemical environments.

Design and Characterization of a Novel Upward Flow Reactor for the Study of High-Temperature Thermal Reduction for Solar-Driven Processes

The design and characterization of an upward flow reactor (UFR) coupled to a high flux solar simulator (HFSS) under vacuum is presented. The UFR was designed to rapidly heat solid samples with concentrated irradiation to temperatures greater than 1000 °C at heating rates in excess of 50 K/s. Such conditions are ideal for examining high-temperature thermal reduction kinetics of reduction/oxidation-active materials by temporally monitoring O2 evolution. A steady-state, computational fluid dynamics (CFD) model was employed in the design to minimize the formation of eddies and recirculation, and lag and dispersion were characterized through a suite of O2 tracer experiments using deconvolution and the continuously stirred tank reactors (CSTR) in series models. A transient, CFD and heat transfer model of the UFR was combined with Monte Carlo ray tracing (MCRT) to determine radiative heat fluxes on the sample from the HFSS to model spatial and temporal sample temperatures. The modeled temperatures were compared with those measured within the sample during an experiment in which Co3O4 was thermally reduced to CoO and O2. The measured temperatures within the bed were bounded by the average top and bottom modeled bed temperatures for the duration of the experiment. Small variances in the shape of the modeled versus experimental temperatures were due to contact resistance between the thermocouple and particles in the bed and changes in the spectral absorptivity and emissivity as the Co3O4 was reduced to CoO and O2.

Enhanced mechanical, thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-temperature thermal reduction

Graphene aerogels with high surface areas, ultra-low densities and thermal conductivities have been prepared to exploit their wide applications from pollution adsorption to energy storage, supercapacitor, and thermal insulation. However, the low mechanical properties, poor thermal stability and electric conductivity restrict these aerogels’ applications. In this paper, we prepared mechanically strong graphene aerogels with large BET surface areas, low thermal conductivities, high thermal stability and electric conductivities via hydrothermal reduction and supercritical ethanol drying. Annealing at 1500 °C resulted in slightly increased thermal conductivity and further improvement in mechanical properties, oxidation temperature and electric conductivity of the graphene aerogel. The large BET surface areas, together with strong mechanical properties, low thermal conductivities, high thermal stability and electrical conductivities made these graphene aerogels feasible candidates for use in a number of fields covering from batteries to sensors, electrodes, lightweight conductor and insulation materials.

Ge Nanoparticles Encapsulated in Nitrogen-Doped Reduced Graphene Oxide as an Advanced Anode Material for Lithium-Ion Batteries

Ge nanoparticles/C composites are desirable electrode materials for high energy and power density lithium-ion batteries. However, the production of well-dispersed Ge nanoparticles in a carbon network remains a challenge because of rapid grain growth during high-temperature thermal reduction. Herein, we report a PVP-assisted hydrolysis approach for fabricating a Ge nanoparticles/reduced graphene oxide composite (denoted as Ge/RGO) made of ∼5 nm Ge nanoparticles that are uniformly distributed within a nitrogen-doped RGO carbon matrix. The Ge/RGO composite exhibits an initial discharge capacity of 1475 mA h g–1 and a reversible capacity of 700 mA h g–1 after 200 cycles at a current density of 0.5 A g–1. Moreover, Ge/RGO shows a capacity of 210 mA h g–1 even at a high current density of 10 A g–1. The excellent performance of the Ge/RGO composite is attributed to its unique nanostructure, including Ge nanoparticles, homogeneous particle distribution, and highly conductive RGO carbon matrix. These properties alleviate the pulverization problem, prevent Ge particle aggregation, and facilitate electron and lithium-ion transportation.

The Preparation of Graphene via Thermal Reduction Method

In this paper, the graphene oxide reducing by photochemical-thermal reduction and high-temperature thermal reduction was studied to get qualified graphene and avoid the re-aggregation. The results show that graphene obtained by both of the two reduction methods all maintained the original well-layered morphology of the graphene oxide. The graphene had smooth surface and high quality as completely reduced by high-temperature thermal method. However, the reduction the photochemical-thermal reaction was not sufficient and caused many vesicles on the graphene surface due to the low temperature and the lack of reaction time.

Isothermal kinetics of mechanochemically and thermally synthesized Ag from Ag2O

The kinetics of isothermal reduction of Ag2O with graphite under argon atmosphere for a non-activated sample and mechanically activated sample was investigated. It is found that Johnson–Mehl–Avrami model appropriately explained the thermal and mechanochemical synthesis of Ag from Ag2O+ghraphite mixture. The process kinetics was investigated using the same approach for milled and unmilled samples. The results show that the Avrami exponent of mechanochemical reduction is higher than that of high temperature thermal reduction. Also, the mechanisms of nuclei growth in thermal and mechanochemical reduction are diffusion controlled and interface controlled, respectively.

CO2valorisation based on Fe3O4/FeO thermochemical redox reactions using concentrated solar energy

The solar-driven dissociation of CO2 by thermochemical looping via Fe3O4/FeO redox reactions is considered. The process recycles and upgrades CO2 to ultimately produce chemical synthetic fuels from high-temperature solar heat and abundant feedstock as only inputs. The two-step process encompasses the endothermic reduction of Fe3O4 to FeO and O2 using concentrated solar energy as the high-temperature source for reaction enthalpy and the nonsolar exothermic oxidation of FeO with CO2 to generate CO. The resulting Fe3O4 is then recycled to the first step and carbon monoxide can be further processed to syngas and serve as the building block to synthesise various synfuels by catalytic processes. This study examines the thermodynamics and kinetics of the pertinent reactions. The high-temperature thermal reduction of Fe3O4 is realised above the oxide melting point by using concentrated solar thermal power. The reactivity of the synthesised FeO-rich material with CO2 at moderate temperature is then investigated by thermogravimetry. FeO conversion higher than 90% can be achieved with reaction rates depending on temperature, particle size and CO2 concentration. The solar-produced nonstoichiometric FeO is more reactive with CO2 than commercial pure FeO. Activation energies of 57 and 68 kJ/mol are derived from a kinetic analysis of the CO2-splitting reaction in the range of 600 °C to 800 °C with solar and commercial FeO, respectively. Copyright © 2012 John Wiley & Sons, Ltd.

Stability and Formation Mechanisms of Carbonyl- and Hydroxyl-Decorated Holes in Graphene Oxide

By use of molecular dynamics simulations, we have studied the evolution of epoxy and hydroxyl functional groups on graphene oxide (GO) during high-temperature thermal reduction. We find that the reduced GO sheets are characterized by a large number of stable holelike defects formed by breaking of C−C bonds in the basal plane. These defects are always decorated by the carbonyl (C═O) groups and are formed due to the strain in the basal plane created by epoxy and hydroxyl functional groups that are located close to each other. With very few exceptions, the carbonyl groups that are observed in Raman spectroscopy and other experimental studies are generally attributed to the C═O terminations of the edges. However, our study using first-principles calculations and a reactive force field approach clearly shows that the formation of carbonyl groups within the graphene basal plane is energetically favorable compared to other well-known functional groups such as epoxies and ethers. We have identified the specific r...

Monoclinic zirconia-supported Fe 3O 4 for the two-step water-splitting thermochemical cycle at high thermal reduction temperatures of 1400–1600 °C

Two-step thermochemical water-splitting using monoclinic ZrO 2-supported Fe 3O 4 (Fe 3O 4/ m-ZrO 2) for hydrogen production was examined at high thermal reduction temperatures of 1400–1600 °C. After thermal reduction of Fe 3O 4/ m-ZrO 2, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 °C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe 3O 4 on a m-ZrO 2 support and the conversion of Fe 3O 4 to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe 3O 4-to-FeO conversion reached 60% when the Fe 3O 4/ m-ZrO 2 was thermally reduced at 1600 °C. The phase transition of m-ZrO 2 support to tetragonal ZrO 2 ( t-ZrO 2) did not occur during the thermal reduction at 1400–1500 °C, but it did proceed slightly at 1600 °C. Fe ions from Fe 3O 4 did not enter the ZrO 2 lattice during high-temperature thermal reduction. Thus, the Fe 3O 4 loaded on a m-ZrO 2 support can continuously contribute as a Fe 3O 4–FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400–1600 °C.

Oxygen chemisorption on V 2O 5: Isotherms and isobars of adsorption

The two-step cycle for solar-thermochemical fuels production and thermochemical energy storage benefits from low oxygen partial pressure in the high-temperature thermal reduction step. To be practical, low oxygen partial pressures must be reached by energetically efficient and economically affordable methods—a challenge currently not met by either mechanical vacuum pumping or by inert gas sweeping. To address this challenge, we have examined a promising, thermally-driven surface adsorption/desorption approach. Providing that appropriately designed materials can be identified as expected, this approach would substantially advance solar-thermochemical fuel production (water and carbon dioxide splitting), thermochemical energy storage, and related technologies.