Cr(N,C) diffusion coating formation on pre-nitrocarburised H13 tool steel

The microstructural processes of Cr(N,C) coating formation by thermoreactive deposition and diffusion (TRD) on pre-nitrocarburised H13 tool steel were studied. Both nitrocarburising and TRD were performed in fluidized bed furnaces at 570 °C. During TRD, chromium was transferred from chromium powder in the fluidized bed, to the nitrocarburised substrates by gas-phase reactions initiated by reaction of HCl gas with the chromium. Addition of 30% H2 to the input inert gas was found to increase the rate of coating formation, although hydrogen reduction resulted in rapid loss of nitrogen to the surface. The reason for the increased rate of coating formation could not be established without further investigation, although several possible explanations have been proposed. It was found that porosity and the formation of an iron nitride ‘cover layer’ during nitrocarburising were the biggest influences on the microstructure of the Cr(N,C) coating. Microstructural characterization of the coatings was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES).

Fast ion conduction in an acid doped pentaglycerine plastic crystal

High proton conductivity has been achieved in the high temperature plastic crystal phase of pentaglycerine when doped with strong acids, including trifluoromethanesulfonic acid (triflic acid) and methanesulfonic acid. The solid–solid phase transition from the ordered to plastic phase in this material occurs at 86 °C and conductivities of 10^{− 3} S/cm were measured in the high temperature plastic phase on the addition of 1 mol% triflic acid. In the case of methanesulfonic acid, the conductivities showed a greater dependence on acid concentration and were lower than for triflic acid, as expected on the basis of acid strengths. Electrochemical characterisation shows a clear hydrogen reduction process indicating that the proton is the mobile species in the plastic phase.

Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

Mixtures of the plastic crystal material choline dihydrogen phosphate [Choline][DHP] and phosphoric acid, from 4.5 mol% to 18 mol% H₃PO₄, were investigated and shown to have significantly higher proton conductivity compared to the pure [Choline][DHP]. This was particularly evident from the electrochemical hydrogen reduction reaction and the proton NMR diffusion measurements, in addition to ionic conductivity measured from the impedance spectroscopy. The ionic conductivity was observed to increase by more than an order of magnitude in phase I (i.e. the highest temperature solid phase in [Choline][DHP]) reaching up to 10⁻² S cm⁻¹. The multinuclear NMR spectroscopy data suggest that, at least on the timescale of the NMR measurement, the H⁺ cations and [DHP] anions are equivalent in both phases. The pulsed field gradient NMR diffusion measurements of the 18 mol% acid sample indicate that all three ions are mobile, however the H⁺ diffusion coefficient is an order of magnitude higher than for the [Choline] cation or the [DHP] anion, and therefore conduction in these materials is dominated by proton conductivity. The thermal stability, as measured by TGA, is unaffected with increasing acid additions and remains high; i.e. no significant mass loss below 200 °C.

Photocatalytic production of methane and hydrogen through reduction of carbon dioxide with water using titania pellets

This paper presents an experimental study on employing a pellet form of catalyst in photo-reduction of carbon dioxide with water. Water was first absorbed into titania pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing the wet pellets, which were then illuminated continuously for 65 hours using UVC lamps. Analysing the products accumulated in the reactor confirmed that methane and hydrogen were produced through photo-reduction of carbon dioxide with water. No other hydrocarbons were detected. Increasing the temperature in the reactor has showed little change on the amount of methane produced.

Kinetic modelling for photosynthesis of hydrogen and Methane through catalytic reduction of carbon dioxide with water vapour

In a photocatalytic reduction process when products formed are not effectively desorbed, they could hinder the diffusion of intermediates on the surface of the catalyst, as well as increase the chance of collisions among the products, resulting photo-oxidation in a reserve reaction on the surface. This paper analyses a simple kinetic model incorporating the coupled effect of the adsorptive photocatalytic reduction and oxidation. The development is based on Langmuir–Hinshelwood mechanism to model the formation rates of hydrogen and methane through photocatalytic reduction of carbon dioxide with water vapour. Experimental data obtained from literatures have achieved a very good fit. Such model could aid as a tool for related areas of studies. A comparative study using the model developed, showed that product concentration in term of ppm would be an effective measurement of product yields through photocatalytic reduction of carbon dioxide with water vapour.

The voltammetric reduction, deprotonation and surface activity of ruthenium photovoltaic sensitizers in acetone

The reductive voltammetry of the photovoltaic sensitizer [(H2-dcbpy)2Ru(NCS)2] (H2-dcbpy=2,2′-bipyridine-4,4′-dicarboxylic acid) and [(H3-tctpy)Ru(NCS)3]− (H3-tctpy=2,2′:6′,2″-terpyridine-4,4′,4″-tricarboxylic acid) has been investigated in acetone. Significant surface interactions at both platinum and glassy carbon electrodes occur at 0.6 V prior to the reversible potential expected for ligand-based reduction process of the fully protonated acids. The origin of the surface interactions are attributed to the acid–base behaviour of the compounds, combined with overall deprotonation and reduction to hydrogen, since repetitive cycling of the potential reveals well-defined reversible reduction processes in the negative potential range, resulting from formation of doubly deprotonated [(H-dcbpy−)2Ru(NCS)2]2− and singly deprotonated [(H2-tctpy−)Ru(NCS)3]2−, respectively. The extent of the surface interactions has been estimated by electrochemical quartz crystal microbalance and chronocoulometric measurements. Under certain conditions, a thick conducting polymer consisting of several hundred monolayers is formed.

Photosynthesis of hydrogen and methane as key components for clean energy system

While researchers are trying to solve the world's energy woes, hydrogen is becoming the key component in sustainable energy systems. Hydrogen could be produced through photocatalytic water-splitting technology. It has also been found that hydrogen and methane could be produced through photocatalytic reduction of carbon dioxide with water. In this exploratory study, instead of coating catalysts on a substrate, pellet form of catalyst, which has better adsorption capacity, was used in the photo-reduction of carbon dioxide with water. In the experiment, some water was first absorbed into titanium dioxide pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing these wet pellets, which were then illuminated continuously using UVC lamps. Gaseous samples accumulated in the reactor were extracted at different intervals to analyze the product yields. The results confirmed that methane and hydrogen were photosynthesized using pellet form of TiO₂ catalysts. Hydrogen was formed at a rate as high as 0.16 micromoles per hour (μmol h⁻¹). The maximum formation rate of CH₄ was achieved at 0.25 μmol h⁻¹ after 24 h of irradiation. CO was also detected.

Use of residual hydrogen to produce CP-Ti powder compacts for low temperature rolling

The present work investigates the optimal level of residual hydrogen in partially de-hydrogenated powder to produce CP-Ti plate compacts using ECAP with back pressure which are subsequently rolled at low temperature. A comparative study of the compaction of two TiH₂ powders and a CP-Ti powder, with particle sizes 150 um, 50um and 45 um respectively, has been carried out. The hydride powders have also been compacted in a partially de-hydrogenated state. The optimal level of residual hydrogen with respect to the density of the resulting compact and the associated mechanical properties has been defined. ECAP at 300°C produced compacts from these partially de-hydrogenated powders of 99.5% theoretical density, while CP-Ti was compacted to almost full theoretical density under the same ECAP conditions. Therefore, the compaction of powder by ECAP does not benefit from temporary hydrogen alloying.

These compacts then were rolled at temperatures ranging from room temperature to 500°C with an 80% reduction in a single pass. Heat treatment after the rolling can modify the microstructure to improve the resulting mechanical properties and in this regard the temporary alloying with hydrogen has been observed to offer some significant benefits. It is shown the ECAP followed by low temperature rolling is a promising route to the batch production of fully dense CP-Ti wrought product from powder feedstock that avoids the need to subject the material to temperatures greater than 500°C. This low temperature route is expected to be efficient from an energy point of view and it also avoids the danger of interstitial contamination that accompanies most high temperature powder processing.

Conducting polymer composite materials for hydrogen generation

A novel conducting polymer/non-conducting polymer composite (PEDOT/PEG), produced by vapor phase polymerization of PEDOT in the presence of PEG, shows stable electrocatalytic reduction of protons to hydrogen with conversion currents and over-potential comparable to platinum. The swelling of the composite by PEG and especially its ability to coordinate protons seems to be essential for the catalytic activity of the composite.

Ultrasensitive hydrogen sensor based on Pd0-loaded SnO2 electrospun nanofibers at room temperature

Pd0-loaded SnO2 nanofibers have been successfully synthesized with different loaded levels via electrospinning process, sintering technology, and in situ reduction. This simple strategy could be expected to extend for the fabrication of similar metal?oxide loaded nanofibers using different precursors. The morphological and structural characteristics of the resultant product were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). To demonstrate the usage of such Pd0-loaded SnO2 nanomaterial, a chemical gas sensor has been fabricated and investigated for H2 detection. The sensing performances versus Pd0-loaded levels have been investigated in detail. An ultralow limit of detection (20 ppb), high response, fast response and recovery, and selectivity have been obtained on the basis of the sensors operating at room temperature. The combination of SnO2 crystal structure and catalytic activity of Pd0-loaded gives a very attractive sensing behavior for applications as real-time monitoring gas sensors.

Highly stable external short-circuit-assisted oxygen ionic transport membrane reactor for carbon dioxide reduction coupled with methane partial oxidation

A membrane reactor allows for simultaneous separation and reaction, and thus, can play a good role to produce value-added chemicals. In this work, we demonstrated such a membrane reactor based on fluorite oxide samarium-doped ceria (SDC) using an external short-circuit concept for oxygen permeation. The fluorite phase was employed to impart its high structural stability, while its limited electronic conductivity was overcome by the application of an external short circuit to function the SDC membrane for oxygen transport. On one side of the membrane, i.e., feed side, carbon dioxide decomposition into carbon monoxide and oxygen was carried out with the aid of a Pt or Ag catalyst. The resultant oxygen was concurrently depleted on the membrane surface and transported to the other side of the membrane, favorably shifting this equilibrium-limited reaction to the product side. The transported oxygen on the permeate side with the aid of a GdNi/Al2O3 catalyst was then consumed by the reaction with methane to form syngas, i.e., carbon monoxide and hydrogen. As such, the required driving force for gas transport through the membrane can be sustained by coupling two different reactions in one membrane reactor, whose stability to withstand these different gases at high temperatures is attained in this paper. We also examined the effect of the membrane thickness, oxygen ionic transport rate, and CO2 and CH4 flow rates to the membrane reactor performance. More importantly, here, we proved the feasibility of a highly stable membrane reactor based on an external short circuit as evidenced by achieving the constant performance in CO selectivity, CH4 conversion, CO2 conversion, and O2 flux during 100 h of operation and unaltered membrane structure after this operation together with the coking resistance.

Toward design of synergistically active carbon-based catalysts for electrocatalytic hydrogen evolution

Replacement of precious Pt catalyst with cost-effective alternatives would be significantly beneficial for hydrogen production via electrocatalytic hydrogen evolution reaction (HER). All candidates thus far are exclusively metallic catalysts, which suffer inherent corrosion and oxidation susceptibility during acidic proton-exchange membrane electrolysis. Herein, based on theoretical predictions, we designed and synthesized nitrogen (N) and phosphorus (P) dual-doped graphene as a nonmetallic electrocatalyst for sustainable and efficient hydrogen production. The N and P heteroatoms could coactivate the adjacent C atom in the graphene matrix by affecting its valence orbital energy levels to induce a synergistically enhanced reactivity toward HER. As a result, the dual-doped graphene showed higher electrocatalytic HER activity than single-doped ones and comparable performance to some of the traditional metallic catalysts.

Hydrogen evolution by a metal-free electrocatalyst

Electrocatalytic reduction of water to molecular hydrogen via the hydrogen evolution reaction may provide a sustainable energy supply for the future, but its commercial application is hampered by the use of precious platinum catalysts. All alternatives to platinum thus far are based on nonprecious metals, and, to our knowledge, there is no report about a catalyst for electrocatalytic hydrogen evolution beyond metals. Here we couple graphitic-carbon nitride with nitrogen-doped graphene to produce a metal-free hybrid catalyst, which shows an unexpected hydrogen evolution reaction activity with comparable overpotential and Tafel slope to some of well-developed metallic catalysts. Experimental observations in combination with density functional theory calculations reveal that its unusual electrocatalytic properties originate from an intrinsic chemical and electronic coupling that synergistically promotes the proton adsorption and reduction kinetics.

Sub-lethal UV-C radiation induces callose, hydrogen peroxide and defence-related gene expression in Arabidopsis thaliana

Exposure of plants to UV-C irradiation induces gene expression and cellular responses that are commonly associated with wounding and pathogen defence, and in some cases can lead to increased resistance against pathogen infection. We examined, at a physiological, molecular and biochemical level, the effects of and responses to, sub-lethal UV-C exposure on Arabidopsis plants when irradiated with increasing dosages of UV-C radiation. Following UV-C exposure plants had reduced leaf areas over time, with the severity of reduction increasing with dosage. Severe morphological changes that included leaf glazing, bronzing and curling were found to occur in plants treated with the 1000 J·m(-2) dosage. Extensive damage to the mesophyll was observed, and cell death occurred in both a dosage- and time-dependent manner. Analysis of H2 O2 activity and the pathogen defence marker genes PR1 and PDF1.2 demonstrated induction of these defence-related responses at each UV-C dosage tested. Interestingly, in response to UV-C irradiation the production of callose (β-1,3-glucan) was identified at all dosages examined. Together, these results show plant responses to UV-C irradiation at much lower doses than have previously been reported, and that there is potential for the use of UV-C as an inducer of plant defence.