Performance of CoNiO spinel oxide coating on AISI 430 stainless steel as interconnect for intermediate temperature solid oxide fuel cell

In order to decrease oxide growth kinetics, maintain suitable conductivity and prevent Cr-volatilization of AISI 430 stainless steels (430 SS) as the interconnect for intermediate temperature solid oxide fuel cells (SOFCs), a CoNiO spinel oxide protective coating has been successfully fabricated on the 430 SS specimen using a simple and cheap process with two steps: 1) electroplation of CoNi alloy layer and 2) pre-oxidation treatment to convert the CoNi alloy into spinel oxide. The CoNiO spinel layer on the 430 SS (CoNiO 430 SS) is dense and uniform with 8–10 μm thickness. And the CoNiO spinel oxide protective coating consists of a main face-centered-cubic (fcc) NiCo₂O₄ spinel phase and a minor fcc NiO phase. Compared with bare 430 SS, the oxidation resistance and the conductivity of the CoNiO 430 SS have been improved remarkably under simulated typical SOFC operating cathode conditions (at 800 °C in air). After an isothermal oxidation test at 800 °C, the area specific resistance (ASR) of CoNiO 430 SS is much lower and stable (0.1 Ω cm² for 100 h and 0.9 Ω cm² for 600 h) than that of bare 430 SS (1.2 Ω cm² for 100 h and 2.4 Ω cm² for 600 h). These performances of CoNiO 430 SS imply that it can be a promising candidate interconnect for solid oxide fuel cell.     

Hydrogen storage properties of nanocrystalline Mg2Ni prepared from compressed 2MgH2Ni powder

In the present work, nanocrystalline Mg₂Ni with an average size of 20–50 nm was prepared via ball milling of a 2MgH₂Ni powder followed by compression under a pressure of 280 MPa. The phase component, microstructure, and hydrogen sorption properties were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), pressure-composition-temperature (PCT) and synchronous thermal analyses (DSC/TG). Compared to the non-compressed 2MgH₂Ni powder, the compressed 2MgH₂Ni pellet shows lower dehydrogenation temperature (290 °C) and a single-phase Mg₂Ni is obtained after hydrogen desorption. PCT measurements show that the nanocrystalline Mg₂Ni obtained from dehydrogenated 2MgH₂Ni pellet has a single step hydrogen absorption and desorption with fairly low absorption (?57.47 kJ/mol H₂) and desorption (61.26 kJ/mol H₂) enthalpies. It has very fast hydrogen absorption kinetics at 375 °C with about 3.44 wt% hydrogen absorbed in less than 5 min. The results gathered in this study show that ball milling followed by compression is an efficient method to produce Mg-based ternary hydrides.     

In situ preparation of N doped orthorhombic Nb2O5 nanoplates /rGO composites for photocatalytic hydrogen generation under sunlight

The synthesis of nitrogen doped orthorhombic niobium oxide nanoplates/reduced graphene oxide composites (NNb₂O₅/rGO) and their photocatalytic activity towards hydrogen generation from water and H₂S under natural sunlight has been demonstrated, uniquely. Nanostructured NNb₂O₅/rGO is synthesized by in situ wet chemical method using urea as a source of nitrogen and optimized by varying percentage of graphene oxide (GO). X?ray diffraction (XRD) study reveals that NNb₂O₅ have orthorhombic crystal structure with crystalline size, 35 nm. Further, X?ray photoelectron spectroscopy (XPS) confirm the presence of nitrogen and rGO in NNb₂O₅/rGO nanocomposite. Morphological features of (NNb₂O₅/rGO) were examined by FE?SEM and FE?TEM showed Nb₂O₅ nanoplates of diameter 25–40 nm anchored on 2D rGO. Diffuse reflectance spectra depicts the extended absorbance in the visible region with band gap of 2.2 eV. Considering the band gap in the visible region, the photocatalytic hydrogen generation from water and H₂S has been performed. The 1 wt % rGO hybridized NNb₂O₅ (S2) exhibited superior photocatalytic hydrogen generation (537 μmol/h) from water and (1385 μmol/h) from H₂S under sunlight. The improved photocatalytic activity is attributed due to an extended absorbance in the visible region, modified electronic structure upon doping and formation of well defined NNb₂O₅/rGO interface, provides large surface area, accelerates the supression of electron and hole pairs recombination rate. In our opinion, this works may provides facile route for energy efficient and economic approach for fabrication of NNb₂O₅/rGO nanocomposites as a visible light active photocatalyst.     

Study on steam reforming of coal tar over NiCo/ceramic foam catalyst for hydrogen production: Effect of Ni/Co ratio

The effect of Ni/Co ratio on the catalytic performance of NiCo/ceramic foam catalyst for hydrogen production by steam reforming of real coal tar was studied. The NiCo/ceramic foam catalyst was synthesized by deposition-precipitation (DP) method and characterized with different methods. The experiments were conducted in a two-stage fixed-bed reactor. The results showed that the reducibility of the metallic oxides in bimetallic NiCo/ceramic foam catalysts was influenced obviously by the Ni/Co ratio.Both gas and hydrogen yield increased first and then decreased with the decline of Ni/Co ratio, and the highest hydrogen yield of 31.46 mmol g^?1 was obtained when the Ni/Co ratio was 5/5. The lowest coke deposition of 0.34 wt% was generated at the same Ni/Co ratio. The lifetime test showed the catalyst maintained catalytic activity after 14 cycles (28 h), indicating the coal tar steam reforming on NiCo/ceramic foam catalyst is a promising method for hydrogen production.     

Numerical analysis of H2 formation during partial oxidation of H2SH2O upon activation of oxidizer by an electric discharge

The numerical analysis of H₂ production during partial oxidation of H₂SH₂O in a plug-flow reactor at atmospheric pressure and a rather low temperature (T₀ = 500 K) was conducted, when the oxidizer (oxygen or air) was preliminarily activated by an electrical discharge with different values of reduced electric field and input energy. It was shown that a significant hydrogen yield in flow reactor can be obtained only after ignition of the mixture. The ignition delay length depends on the reduced electric field E/N and input energy E_s in the discharge and is minimal at E/N～8–10 Td for the discharge in oxygen and at E/N～4–10 and 120–150 Td in air discharge, when O₂(a¹Δ_g) mole fraction in the discharge products is maximal. If the H₂SH₂OO₂(air) mixture ignites inside the flow reactor, the mole fraction of hydrogen and its relative yield do not depend on E/N. The relative hydrogen yield increases monotonically with an addition of water to H₂S. It was found, that the approach based on the partial oxidation of the H₂SH₂O mixture upon activation of oxygen by an electric discharge can ensure very low energy cost for H₂ production. The minimum specific energy requirement, obtained for the H₂SO₂ mixture, was found to be 0.83 eV/(molecule H₂) and 0.18 eV/(molecule H₂S) at atmospheric pressure and can be further decreased if the energy released during partial oxidation of H₂S is spent on heating the reagents. The use of air as an oxidizer requires higher energy costs and seems to be less promising.     

Fabrication of Pt-doped carbon aerogels for hydrogen storage by radiation method

A radiation method was investigated to fabricate Pt-doped carbon aerogels (CAsPt). The physicochemical properties of the pristine CAs and CAsPt were systematically characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and nitrogen adsorption measurements. The results showed that not only a great number of Pt nanospheres but also many Pt nanoparticles presented in the network of CAs after radiation. The influence of Pt doping on the hydrogen uptake capacity of CAs was studied. In comparison with the pristine CAs, it was remarkable that the hydrogen uptake capacity of the CAsPt had been significantly enhanced, which was contributed by the hydrogen spillover of Pt.     

Hydrogen evolution in the dehydrogenation of methylcyclohexane over Pt/CeMgAlO catalysts derived from their layered double hydroxides

Pt/CeMgAl layered double hydroxides with different Ce contents were prepared by one-step co-precipitation method, which underwent calcination and reduction with hydrogen and were finally converted into Pt/CeMgAlO catalysts. These catalysts were tested in the dehydrogenation of methylcyclohexane (MCH) into toluene to produce hydrogen. The addition of CeO₂ promoted the dispersion of Pt and decreased the Pt particle size. During the dehydrogenation reaction, toluene was the only liquid product and its selectivity was higher than 99.9%. MCH conversion increased with the reaction temperature rising. The conversion and hydrogen evolution rate on Pt/Ce₁₄MgAlO350 reached up to 98.5% and 1358.6 mmol/g_Pt/min at 350 °C. Moreover, Pt/CeMgAlO catalysts exhibited no acidity and presented a high anti-coking ability and good stability. These results suggest that Pt/CeMgAlO catalysts have potential industrial application for hydrogen energy utilization.     

Catalytic transformation of H2S for H2 production

Hydrogen sulfide (H₂S) gas is a by-product from natural gas refining, hydrodesulfurization of various fossil fuels, and syngas cleaning from pyrolysis and gasification. Catalytic pyrolysis of H₂S provides an alternative and effective pathway to recover both H₂ and sulfur. Catalysts from hydrotalcite of ZnAl, ZnNiAl, and ZnFeAl were employed for H₂S pyrolysis and compared with TiO₂ and MoS₂ at atmospheric pressure and temperatures in the range of 923–1123 K. Kinetic analysis was carried out in a packed bed reactor which revealed the effect of H₂S partial pressures to be of the order of 0.8–1 with respect to H₂S. The developed novel catalysts showed improved performance with significantly reduced activation energy compared to TiO₂ by 30 kJ/mol as well as higher H₂S conversion during pyrolysis (17% at 1173 K) than with MoS₂ catalyst, even at high H₂S partial pressure which is necessary for viable hydrogen production. The new approach showed an alternate economical and efficient pathway of catalyst design to obtain high activity and stability for simultaneous H₂ energy and pure sulfur recovery from unwanted H₂S resources.     

PtRh alloys on hybrid TiO2 – Carbon support as high efficiency catalyst for ethanol oxidation

High cost and poor stability of catalysts remain major obstacles for the commercialization of direct ethanol fuel cells (DEFCs). In this work, a Pt₉Rh/TiO₂C nanostructured catalyst is synthesized via an impregnation-reduction method followed by thermal annealing in N₂ at ambient pressure. X-ray powder diffraction (XRD) and scanning transmission electron microscopy (STEM) are used to characterize the corresponding physico-chemical properties of the as-prepared catalysts. The results reveal that PtRh nanoparticles are uniformly distributed on the TiO₂C hybrid support material. Cyclic voltammetry, linear scan voltammetry, CO-stripping voltammograms, chronoamperometry and chronopotentiometry methods are employed to investigate their catalytic performance for ethanol oxidation. The results show that the Pt₉Rh/TiO₂C produced a current density of 1039.5 mA mg_Pt^?1, which are 3.98, 8.31 and 2.43 times higher than Pt/TiO₂C, Pt/C and Pt₉Rh/C, respectively. Furthermore, the Pt₉Rh/TiO₂C also has greater resistance to CO-poisoning and displays better stability for ethanol oxidation than other catalysts. Pt₉Rh/TiO₂C therefore provides a promising material for ethanol oxidation in direct ethanol fuel cells.     

Improved performance of 3CSiC photocathodes by using a pn junction

To improve the performance of 3CSiC photocathodes, we formed a pn junction at the 3CSiC surface. Using current–voltage measurements for Schottky contacts on 3CSiC, the Schottky barrier height and depletion layer width of 3CSiC having a pn junction was observed to be larger than those of 3CSiC without the junction. By measuring photocurrent and spectral responses, the 3CSiC photocathodes with the pn junction exhibited larger photocurrent and higher quantum efficiencies compared with 3CSiC without the pn junction. Using a Pt cocatalyst on the 3CSiC photocathode with the pn junction, the solar-to-hydrogen energy conversion efficiency was measured at 0.72%.     

Different modified multi-walled carbon nanotube–based anodes to improve the performance of microbial fuel cells

To clearly illustrate the activity effect of multi-walled carbon nanotubes (MWCNTs) and their functionality on anodic exoelectrogen in microbial fuel cells (MFCs), the growth of E. coli and anode biofilm on MWCNT-, MWCNTCOOH and MWCNTNH₂ modified anodes were compared with a bare carbon cloth anode. The activity effect was characterized by the amount of colony-forming units (CFUs), activity biomass, morphology of biofilms and cyclic voltammetric (CV). The results showed that MWCNTs, MWCNT-COOH and MWCNT-NH₂ exhibited good biocompatibility on exoelectrogenic bacteria. The performance of MFCs were improved through the introduction of MWCNT-modified anodes, especially in the presence of COOH/NH₂ groups. The MFCs with the MWCNTCOOHmodified anode achieved a maximum power density of 560.40 mW/m², which was 49% higher than that obtained with pure carbon cloth. In conclusion, the positive effects of MWCNTs and their functionality were evaluated for promoting biofilm formation, biodegradation and electron transfer on anodes. Specifically, the MWCNTCOOHmodified anode demonstrated the largest application potential for the development of MFCs.     

Aqueous phase reforming of polyols for hydrogen production using supported PtFe bimetallic catalysts

3-D cubic ordered mesoporous carbon (CMK-9) supported PtFe bimetallic catalysts with a range of PtFe compositions were applied to the aqueous phase reforming (APR) of polyols for hydrogen production. The catalytic performance with respect to the polyol and support used was also studied. The catalysts and supports were characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N₂ sorption, temperature programmed reduction (TPR), and CO chemisorption techniques. The polyols investigated include ethylene glycol (EG), glycerol, xylitol, and sorbitol. It was found that the addition of Fe to the Pt/CMK-9 catalyst significantly improved catalytic performance, with the optimum Pt:Fe ratio for APR activity being 1:3. It was also observed that, in the PtFe (1:3) system, the CMK-9 support demonstrated better catalytic performance than commercially available activated carbon or alumina. In addition, the catalytic activity of the PtFe/CMK-9 catalyst was successfully increased by both the effect of the water-gas shift reaction, promoted by Fe addition to Pt, and by the structural properties and nature of the CMK-9 support. Moreover, the PtFe (1:3)/CMK-9 catalyst showed efficient catalytic activity for different biomass derivatives (EG, glycerol, xylitol, and sorbitol), with the activity decreasing with increase in the number of carbon atoms.     

AuCu alloys deposited on titanium dioxide nanosheets for efficient photocatalytic hydrogen evolution

This work first reports AuCu alloys deposited on the surface of TiO₂ nanosheets (TiNs) to form heterojunction. A simple deposition-precipitation method was used to construct a new type of AuCu/TiNs heterostructures through gradually depositing Au and Cu nanoparticles on TiNs. Such structures served the dual advantage of constructing a heterostructure which can improve visible light absorption, and the formation of a Schottky barrier between AuCu alloys (lower Fermi level) and TiNs (higher Fermi level) which can suppress the recombination of photo-generated charge carriers to improve the overall photocatalytic activity. The mass ratio of Au and Cu in the AuCu/TiNs heterostructures and the sequence and method of their deposition are found to be the important factors which affect the photocatalytic performance. When the mass ratio of Au to Cu was determined to be 1: 1, the AuCu/TiNs heterostructure exhibited the best photocatalytic performance for hydrogen production from water splitting (over 9 times than TiNs, 1.47 times than Au/TiNs, and 1.75 times than Cu/TiNs).     

First-principles study of hydrogen behavior in vanadium-based binary alloy membranes for hydrogen separation

Vanadium-based alloys are considered to be one of the most promising hydrogen separation membranes due to their high hydrogen permeability. In this study, we investigate the dissolution and diffusion behaviors of hydrogen in vanadium-based binary alloys, V₁₅M (where M = Al, Ti, Cr, Fe, Ni and Nb) alloys, using first-principles method based on density functional theory. The dissolution of hydrogen in V₁₅M alloys is affected by both the elastic and electronic properties, but the elastic effect is the main factor. The H solution energies in the alloys follow the sequence: VTi < VNb < VAl < VCr < VNi < VFe, and a smaller atom size increase the H solution energy. Therefore, the addition of alloying elements with smaller atomic sizes can reduce the solubility of hydrogen in vanadium and inhibit hydrogen embrittlement. For hydrogen diffusion, alloying elements Al, Ti and Nb can be good candidates because they have a higher diffusion coefficient. The VTi alloy has the highest hydrogen permeability, but will have serious hydrogen embrittlement due to the increased H solubility.     

Effects of silicon concentration in SOFC alloy interconnects on the formation of oxide scales in hydrocarbon fuels

Oxide scale formations on FeCr alloy interconnects were investigated in anode gas (mixtures of CH₄ and H₂O) atmospheres for solid oxide fuel cells. The silicon concentration in FeCr alloy changed the microstructures of oxide scales, elemental distribution and oxide scale growth rates. Oxide scale is composed of the following phases from surface to inner oxides: FeMn spinel, Cr₂O₃, oxide scale/alloy interface and internal oxides of Si and Al. With decreasing the Si concentration from 0.4 to 0.01 mass%, formation of thin Si and Mn layer was observed inside the FeCr alloy. Oxide scale growth rate constants decreased by lowering the Si concentration in FeCr alloy from 4.2 × 10⁻¹⁸ to 2.1 × 10⁻¹⁸ m² s⁻¹ at 1073 K. Diffusivity of Fe and Cr was changed by the concentration of Si in FeCr alloy, which affects the growth rates of oxide scale. The electrical conductivity of oxidized FeCr alloy shows almost same level regardless the Si concentration (in the orders of 10 S cm⁻² at 1073 K).     

Noble metal-free FeN-CNFs as an efficient electrocatalyst for oxygen reduction reaction

Carbonaceous materials containing non-precious metal atoms and doped with nitrogen have enthralled stunning attention in the field of electrochemical energy conversion systems. Herein, we demonstrated a facile method to fabricate iron and nitrogen doped carbon nanofiber (FeN-CNFs) catalyst material from ferric chloride and interfacial synthesized polyaniline (PANI) nanofibers, by carbonization process in an inert atmosphere at 800 °C. Further, synthesized material was characterized by elemental analysis and X-ray photoelectron spectroscopy (XPS) that confirms the presence of FeN bonds. The structural and morphological features are studied using various microscopy and spectroscopy techniques. The oxygen reduction reaction (ORR) activity of synthesized catalyst materials was examined by rotating disk electrode experiments in 0.1 M KOH. Among all these synthesized materials FeN-CNFs material showed enhanced ORR activity regarding current density and onset potential. Also, FeN-CNFs catalyst exhibited tolerance to methanol and durability in comparison to commercial Pt/C catalyst. The superior performance of FeN-CNFs may be attributed due to the introduction of Fe and formation of FeN bond in catalyst material.     

One-pot synthesis of ultrasmall PtAg nanoparticles decorated on graphene as a high-performance catalyst toward methanol oxidation

A one-pot synthesis method is utilized for the fabrication of ultrasmall platinum-silver nanoparticles decorated on graphene (PtAg/G) catalyst. This method has several advantages such as inexpensiveness, simplicity, low temperature, surfactant free, reductant free, being environmentally friendly and greenness. In this work, graphene and silver formate were dispersed in ultrapure water in an ultrasonic bath at 25 °C followed by through a galvanic displacement reaction; to prepare PtAg/G, PtCl₂ was added to the suspension under mild stirring condition. The morphology, crystal structure and chemical compositions of the as-fabricated PtAg/G and Pt/C catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Energy dispersive X-ray spectroscopy (EDS) techniques. Electrochemical techniques, including cyclic voltammetry (CV) and chronoamperometry (CA) measurements were used to analyze the electrochemical activity of the PtAg/G and Pt/C catalysts. The TEM images illustrate the uniform distribution of ultrasmall PtAg nanoparticles with the average size of 2–3 nm on the graphene nanosheets. The PtAg/G promoted the current density 2.46 times as much as Pt/C with a negative shift in onset oxidation potential and peak potential for oxidation reaction of methanol. Besides, the novel PtAg/G catalyst shows large electrochemically active surface area, lower apparent activation energy, and higher levels of durability in comparison to the Pt/C catalyst for the oxidation of methanol. The PtAg/G catalyst depicts extraordinary catalytic performance and stability to those of the Pt/C catalyst toward methanol oxidation in alkaline media.     

Hydrogen-iodide decomposition over PdCeO2 nanocatalyst for hydrogen production in sulfur-iodine thermochemical cycle

A highly active and stable catalyst for hydrogen-iodide decomposition reaction in sulfur-iodine (SI) cycle has been prepared in the form of PdCeO₂ nanocatalyst by sol-gel method with different calcination temperatures (300 °C, 500 °C, and 700 °C). XRD and TEM confirmed a size around 6–8 nm for PdCeO₂ particles calcined at 300 °C. Raman study revealed large number oxygen vacancies in PdCeO₂-300 when compared to PdCeO₂-500 and PdCeO₂-700. With increase in calcination temperature, the average particle size increased whereas the specific surface area and number of oxygen vacancies decreased. Hydrogen-iodide catalytic-decomposition was carried out in the temperature range of 400°C–550 °C in a quartz-tube, vertical, fixed-bed reactor with 55 wt % aqueous hydrogen-iodide feed over PdCeO₂ catalyst using nitrogen as a carrier gas. PdCeO₂-300 showed hydrogen-iodide conversion of 23.3%, which is close to the theoretical equilibrium conversion of 24%, at 550 °C. It also showed a reasonable stability with a time-on-stream of 5 h.     

Efficient visible-light-driven hydrogen evolution over ternary MoS2/PtTiO2 photocatalysts with low overpotential

By surface-decorating PtTiO₂ hybrid catalyst with MoS₂ nanosheets, we prepared a new MoS₂/PtTiO₂ ternary system as high-performance photocatalysts. The ternary MoS₂/PtTiO₂ outperforms both the binary MoS₂TiO₂ and PtTiO₂ systems in photocatalytic hydrogen evolution with an AQY (apparent quantum yield) value of 12.54% at 420 nm, owing to the unique ternary design that creates more efficient electron transport path and electron-hole separation mechanism. Electrochemical characterization showed that the MoS₂/PtTiO₂ ternary electrode afford an efficient pathway of photo-excited electrons from TiO₂ to surface-decorated Pt nanoparticles using MoS₂ and internal Pt nanoparticles as bridges, thus significantly promoting electron transfer, reducing the system overpotential and leading to the activation of more reactive sites. This internal electron transfer pathway (TiO₂ → Pt (internal) → MoS₂ → Pt (surface)) eliminates the need of other metal cocatalysts because the Pt nanoparticles play two roles of storing the conduction band electrons of TiO₂ and acting as co-catalyst for reduction of protons to hydrogen. This unique ternary metal-semiconductor heterojunction for efficient photocatalytic hydrogen evolution provides a meaningful reference for reasonable design of other hybrid photocatalysts.     

Experimental and first principle studies on hydrogen desorption behavior of graphene nanofibre catalyzed MgH2

With the combination of experiment and first-principles theory, we have evaluated and explored the catalytic effects of graphitic nanofibres for hydrogen desorption behaviour in magnesium hydride. Helical form of graphene nanofibres (HGNF) have larger surface area, curved configuration and high density of graphene layers resulting in large quantity of exposed carbon sheet edges. Therefore they are found to considerably improve hydrogen desorption from MgH₂ at lower temperatures compared to graphene (onset desorption temperature of MgH₂ catalyzed by HGNF is 45 °C lower as compared to MgH₂ catalyzed by graphene). Using density functional theory, we find that graphene sheet edges, both the zigzag and armchair type, can weaken MgH bonds in magnesium hydride. When the MgH₂ is catalyzed with higher electronegative and reactive graphene edge of graphene, the electron transfer occurs from Mg to carbon, due to which MgH₂ is dissociated into hydrogen and MgH component. The Mg gets bonded with the graphene edge carbon atoms in the form of CMgH and CH bonds. In the as formed CMgH, the graphene edges “grab” more electronic charge as compared to the normal charge donation of Mg to H. This leads to the weakening of the MgH bond, causing hydrogen to desorbs at lower temperatures.