Coated interconnects development for high temperature water vapour electrolysis: Study in anode atmosphere

High temperature water vapour electrolysis (HTE) is an efficient technology for hydrogen production. In this context, a commercial stainless steel, K41X (AISI 441), was chosen as interconnect. In a previous paper, the high temperature corrosion and the electrical conductivity were evaluated in both anode (O₂–H₂O) and cathode (H₂–H₂O) atmosphere at 800 °C. In O₂–H₂O atmosphere, the formation of a thin chromia protective layer was observed. Nevertheless, the ASR parameter measured was higher than the maximum accepted value. These results, in addition with chromium evaporation measurements, proved that the K41X alloy is not suitable for HTE interconnect application. In this study, two perovskite-type oxides La_0.8Sr_0.2MnO_3−δ and LaNi_0.6Fe_0.4O_3−δ were tested as coatings in O₂–H₂O atmosphere at 800 °C. Screen-printing and physical vapour deposition were used as coating processes. The high temperature corrosion resistance and the electrical conductivity were improved, especially with the LaNi_0.6Fe_0.4O_3−δ coating. Cr specie volatility was also reduced.     

High performance solid oxide electrolysis cells using Pr0.8Sr1.2(Co,Fe)0.8Nb0.2O4+δ–Co–Fe alloy hydrogen electrodes

A novel ceramic hydrogen electrode material consisting of K₂NiF₄-type structured Pr_0.8Sr_1.2(Co,Fe)_0.8Nb_0.2O_4+δ (K-PSCFN) matrix with homogenously dispersed nano-sized Co–Fe alloy (CFA) has been demonstrated by annealing perovskite Pr_0.4Sr_0.6Co_0.2Fe_0.7Nb_0.1O_3−δ (P-PSCFN) in H₂ at 900 °C. Impedance spectra and voltage–current density curves of the La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) electrolyte supported solid oxide electrolysis cell (SOEC) with a configuration of K-PSCFN–CFA/LSGM/Ba_0.9Co_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) have been evaluated as a function of the operating temperature and feeding gas absolute humidity (AH) to characterize the cell performance. Cell polarization resistances (R_p) were as low as 0.77 and 0.31 Ω cm² under open circuit voltage (OCV) and 60% absolute humidity (AH) at 800 and 900 °C, respectively. The cell has demonstrated good stability for high temperature stream electrolysis, and a hydrogen production rate of 707 ml/cm² h calculated from the Faraday's law has been achieved under an electrolysis voltage of 1.3 V and 60 vol.% AH at 900 °C. The cell performance results indicate that K-PSCFN–CFA is a promising hydrogen electrode for high temperature solid oxide electrolysis cells.     

La0.75Sr0.25Cr0.5Mn0.5O3 as hydrogen electrode for solid oxide electrolysis cells

La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) has been applied as hydrogen electrode (cathode) material in solid oxide electrolysis cells operating with different steam concentrations (20, 40, 60 and 80 vol.% absolute humidity (AH)) using 40 sccm H₂ carrier gas at 800, 850 and 900 °C, respectively. Impedance spectra and voltage-current curves were measured as a function of cell electrolysis current density and steam concentration to characterize the cell performance. The cell resistance decreased with the increase in electrolysis current density while increased with the increase in steam concentration under the same electrolysis current density. At 1.6 V applied electrolysis voltage, the maximum consumed current density increased from 431 mA cm⁻² for 20 vol.% AH to 593 mA cm⁻² for 80 vol.% AH at 850 °C. Polarization and impedance spectra experiments revealed that LSCM-YSZ hydrogen electrode played a major role in the electrolysis reaction.     

A facile two-step synthesis and dehydrogenation properties of NaAlH4 catalyzed with Co–B

Co–B doped NaAlH₄ is successfully synthesized by two-step synthesis process. The first activation step is milling NaH/Al powder and Co–B mixtures under Ar atmosphere. The second step is milling in a lower hydrogen pressure atmosphere. XRD patterns and FTIR spectrum demonstrate that NaAlH₄ is completely formed after 15 h milling in Ar atmosphere following by 40 h milling in 2 MPa H₂ atmosphere. PCT curves of as-prepared NaAlH₄ show that it can release hydrogen at a low temperature of 90 °C. The activation energy value calculated by Arrhenius equation is only 67.95 kJ mol⁻¹. Moreover, the formation mechanism of NaAlH₄ is also discussed.     

Synthesis and characterization of aluminum-doped perovskites as cathode materials for intermediate temperature solid oxide fuel cells

(Ba_0.5Sr_0.5)(Fe_1-xAl_x)O_3-δ (BSFAx, x = 0–0.2) oxides have been synthesized as novel cobalt-free cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) using a sol-gel method. The BSFAx (x = 0–0.2) materials have been characterized by X-ray diffraction and scanning electron microscopy. The electrical conductivities and electrochemical properties of the prepared samples have also been measured. At 800 °C, the conductivity drops from 15 S cm⁻¹ to 5 S cm⁻¹ when the doping level of aluminum is increased to 20%. The aluminum-doping concentration has important impacts on the electrochemical properties of BSFAx materials. The BSFA0.09 cathode shows a significantly lower polarization resistance (0.26 Ω cm²) and cathodic overpotential value (55 mV at the current density of 0.1 A cm⁻²) at 800 °C. Furthermore, an anode-supported single cell with BSFA0.09 cathode has been fabricated and operated at a temperature range from 650 to 800 °C with humidified hydrogen (∼3vol% H₂O) as the fuel and the static air as the oxidant. A maximum power density of 676 mWcm⁻² has been achieved at 800 °C for the single cell. We believe that BSFA0.09 is a promising cathode material for future IT-SOFCs application.     

Noble fabrication of Ni–Mo cathode for alkaline water electrolysis and alkaline polymer electrolyte water electrolysis

Among the catalysts for hydrogen evolution reaction (HER) in alkaline media, Ni–Mo turns out to be the most active one. Conventional preparations of Ni–Mo electrode involve repeated spraying of dilute solutions of precursors onto the electrode substrate, which is time-consuming and usually results in cracking and brittle electrodes. Here we report a noble fabrication of Ni–Mo electrode for HER. NiMoO₄ powder was synthesized and used as the precursor. After reduction in H₂ at 500 °C, the NiMoO₄ powder layer was converted to a uniform and robust electrode containing metallic Ni and amorphous Mo(IV) oxides. The distribution of Ni and Mo components in this electrode is naturally uniform, which can maximize the interaction between Ni and Mo and benefit the electrocatalysis. The thus-obtained Ni–Mo electrode exhibits a very high catalytic activity toward the HER: the current density reaches 700 mA/cm² at 150 mV overpotential in 5 M KOH solution at 70 °C. This new fabrication method of Ni–Mo electrode is not only suitable for alkaline water electrolysis (AWE), but also applicable to the alkaline polymer electrolyte water electrolysis (APEWE), an emerging technique for efficient production of H₂.     

High- and low- temperature behaviors of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode operating under CO2/H2O-containing atmosphere

High- and low- temperature behaviors of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) cathode for solid oxide fuel cells operating under CO₂/H₂O-containing atmosphere are investigated. LSCF shows different stability against CO₂ and H₂O at high and low temperature. LSCF has excellent electrochemical performance and high stability against the corrosion of CO₂ and H₂O at 750 °C due to weak reactivity of LSCF with CO₂. LSCF shows a serious degradation at 600 °C under operation with O₂–CO₂(2.83%)–H₂O(2.64%), which is ascribed to the impeded oxygen activation and oxygen surface diffusion by surface carbonates and SrCO₃ phases on LSCF surface. Under CO₂(5%)–H₂O(2.81%)–He, LSCF reacts with CO₂ to yield SrCO₃ phases in 400–680 °C, and H₂O aggravates the chemical reaction between CO₂ and LSCF. Taking into account of SrCO₃ phase formation on LSCF, LSCF cathode is stable under operation with O₂–CO₂(2.83%)–H₂O(2.64%) in 680–800 °C, whereas it is unstable below 680 °C. LSCF can be subject to degradation caused by CO₂ and H₂O in air during long-term operation below 680 °C.     

Nanostructured Pt–Fe/C cathode catalysts for direct methanol fuel cell: The effect of catalyst composition

A series of carbon supported Pt–Fe bimetallic nanocatalysts (Pt–Fe/C) with varying Pt:Fe ratio were prepared by a modified ethylene glycol (EG) method, and then heat-treated under H₂–Ar (10 vol%-H₂) atmosphere at 900 °C. The Pt–Fe/C catalysts were characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), energy dispersive analysis by X-rays (EDX) and induced coupled plasma-atomic emission spectroscopy (ICP-AES). XRD analysis shows that Pt–Fe/C catalysts have small crystalline particles and form better Pt–Fe alloy structure with Fe amount increasing. TEM images evidence that small Pt–Fe nanoparticles homogeneously deposited on carbon support and addition of Fe can effectively prevent Pt particles agglomeration. EDX and ICP-AES show that Fe precursor cannot be fully reduced and deposited on carbon support through the adopted EG reduction approach. The electrochemical surface area of Pt–Fe/C catalyst obtained through hydrogen desorption areas in the CV curve increases with Fe atomic percentage increasing from 0 to ca. 50%, and then decreases with more Fe in the Pt–Fe/C catalyst. RDE tests show that the Pt–Fe/C with a Pt:Fe ratio of 1.2:1 and an optimized lattice parameter of around 3.894 Å has the highest mass activity and specific activity to oxygen reduction reaction (ORR). As cathode catalyst, this Pt–Fe/C (Pt:Fe ratio of 1.2:1) exhibits higher direct methanol fuel cell performance at 90 °C than Pt/C and other Pt–Fe/C catalysts, this could be attributed to its smaller particle size and better Pt–Fe alloy structure.     

Fast hydriding Mg–Zr–Mn–Ni alloy compositions for high capacity hydrogen storage application

Hydrogen is one of the best alternative to petroleum as an energy carrier. However, the development of a Hydrogen-based economy requires commercialization of safe and cost-effective Hydrogen storage system. In this paper, alloys belonging to Mg–Zr–Mn–Ni alloy system are synthesized using high energy ball milling method. The particle size evolution, chemical analysis and nano-scaled structures were characterized by using SEM, EDXS and XRD techniques, respectively. The optimized - highest hydrogen storing - alloy has particle size of about 8.36 ± 1.17 μm with crystallite size 16.99 ± 5.48 nm. Hydrogen absorption-desorption measurement is carried out on the principle of pressure reduction method. The alloy coded with MZ1 shows uptake of greater than 7 mass % H₂ at a charging temperature of 200 °C, indicating high gravimetric hydrogen storage capacity at relatively lower hydriding temperature. The optimized Mg–Zr–Mn–Ni alloy also shows considerably enhanced hydriding – dehydriding kinetics, compare to pure Mg.     

Experiment assessment of hydrogen production from activated aluminum alloys in portable generator for fuel cell applications

An experiment assessment of hydrogen production from activated aluminum alloy in portable hydrogen generator for fuel cell applications was investigated. The optimum hydrogen capacity of the high–reactive Al–Bi–NaCl alloys (the abbreviation of milled material of aluminum, bismuth and NaCl particles) is about 9–9.4 wt.%, meeting the targets (9 wt.%) of the US Department of Energy in 2015. Hydrogen production rate can be controlled via controlling the water flow rate in the generator, being 1.369–6.198 L hydrogen/min while the water flow rate ranges in 5–20 mL/min. The larger water flow rate often leads to higher temperature and results in unsafety in the generator as the hydrolysis reaction of aluminum alloy and water releases 15 kJ/g heat. However, the heat problem can be successfully eliminated by using effective cooling stytles, which enable the maximum temperature of Al–H₂O mixture (the abbreviation of hydrolysis products of aluminum alloy in water) controlled less than 474 K even though the water flow rate is 20 mL/min. Therefore, the experiment results show that the portable hydrogen generator from aluminum alloy could supply the CO₂–free, high hydrogen capacity and safe hydrogen for fuel cell applications.     

Chemical-looping steam methane reforming over macroporous CeO2–ZrO2 solid solution: Effect of calcination temperature

Chemical-looping steam methane reforming (CL-SMR) is a novel process for the co-production of pure hydrogen and syngas without purification processes. A series of CeO₂–ZrO₂ mixed oxides were prepared by colloidal crystal templating method with calcination temperature increasing from 450 to 850 °C. The structural characteristic and reducibility of CeO₂–ZrO₂ oxygen carriers were investigated by SEM, XRD and TPR techniques and correlated to their reactivity for CL-SMR. The CeO₂–ZrO₂ mixed oxides calcined at low temperatures (e.g., 450 °C) exhibit a better uniform and three-dimensionally ordered macroporous structure, which enhance the mobility of oxygen species, improving the reducibility of CeO₂–ZrO₂ oxygen carriers. The ordered macroporous structure can lead to a high reactivity for CL-SMR, especially for the hydrogen production in water splitting reaction. It was found that the Ce–Zr-450 sample showed the best performance for H₂ production. After ten redox CL-SMR cycles at 800 °C, the Ce–Zr-450 sample still maintained relatively high hydrogen yield and the three-dimensionally ordered macroporous structure remained in good condition, indicating high reactivity and structural stability.     

Studies on the solubility of hydrogen in molten Pb83Li17 eutectic alloy

Lead–lithium eutectic (Pb₈₇Li₁₇) alloy is a candidate material to be used as a secondary tritium breeder, neutron multiplier and heat transfer agent in the fusion reactor. The tritium thus produced in the alloy may be soluble or appear as a new phase of lithium-tritides and/or lead-tritides, which eventually affect the performance of Pb₈₃Li₁₇ eutectic. Therefore, solubility of tritium in the alloy at the operating conditions of the fusion reactor is a subject matter of investigation. Tritium being the isotope of hydrogen behaves more or less similar to the hydrogen. In the present investigation the solubility of hydrogen in the Pb₈₃Li₁₇ has been investigated as a function of temperature and pressure. It was found that, hydrogen solubility in the Pb₈₇Li₁₇ alloy is almost constant above 350 °C. Hydrogen solubility increases with increase of temperature up to 400 °C. Hydrogen solubility is 120 ppm at 400 °C and 800 Torr hydrogen pressure. The solubility decreases on further rise in temperature from 400 °C. However, at all the temperatures hydrogen solubility increased with increase of partial pressure of hydrogen.     

Experimental study of the vapour–liquid equilibria of HI–I2–H2O ternary mixtures,Part 1: Experimental results around the atmospheric pressure

In the framework of the massive production of hydrogen using the sulfur–iodine thermochemical cycle, the design of the reactive distillation column, chosen by CEA for the HIx section, requires the knowledge of the partial pressures of the gaseous species (HI, I₂, H₂O) in thermodynamic equilibrium with the liquid phase of the HI–I₂–H₂O ternary mixture in a wide range of concentrations up to 270 °C and 50 bar. In the first of these two companion papers, we describe the experimental device which enables the measurement of the total pressure and concentrations of the vapour phase (and thus the knowledge of the partial pressures of the different gaseous species) for the HI–I₂–H₂O mixture in the 20–140 °C range and up to 2 bar. This device is used to carry out a large set of experiments investigating various mixtures with optical on-line diagnostics (FTIR for HI and H₂O, UV–visible for I₂). This leads to the determination of the concentrations in the vapour phase for many experimental conditions, results of which are given in this paper. The companion paper (part 2) describes the experimental device which enables measurements of the total pressure and species concentrations in the vapour phase in the process domain.     

Ternary compounds in the magnesium–titanium hydrogen storage system

Mg–Ti–H samples were mechano-chemically synthesized by ball milling in argon atmosphere or under elevated hydrogen pressure. The detailed reaction mechanism during hydrogen release and uptake during continuous cycling was investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) experiments. The thermal behaviour of the samples and hydrogen desorption properties were examined by simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry (MS) measurements. A ternary Ti–Mg–H compound with a fcc lattice form during mechano-chemical sample preparation in hydrogen atmosphere using metal powders, but not using metal hydrides as reactants. The amount of β-MgH₂ increases during the first hydrogen absorption cycle at 300 °C at the expense of the high-pressure polymorph, γ-MgH₂ and the amount of β-MgH₂ remain constant during the following hydrogenations. This study reveals that the ternary compound tends to absorb increasing amounts of magnesium in the dehydrogenated state during cycling. A strong coupling between the amounts of magnesium in the ternary Ti–Mg–H phase and the formation of magnesium and magnesium hydride during hydrogen release and uptake at 300 °C is observed. The composition and the amount of the Ti–Mg–H phase appear to be similar in the hydrogenated state. Fast absorption–desorption kinetics at 300 °C and lower onset temperatures for hydrogen release is observed for all investigated samples (lowest onset temperature of desorption T_on = 217 °C).     

Influence of catholyte pH and temperature on hydrogen production from acetate using a two chamber concentric tubular microbial electrolysis cell

Microbial electrolysis cells (MECs) could be integrated with dark fermentative hydrogen production to increase the overall system yield of hydrogen. The influence of catholyte pH on hydrogen production from MECs and associated parameters such as electrode potentials (vs Ag/AgCl), COD reduction, current density and quantity of acid needed to control pH in the cathode of an MEC were investigated. Acetate (10 mM, HRT 9 h, 24 °C, pH 7) was used as the substrate in a two chamber MEC operated at 600 mV and 850 mV applied voltage. The effect of catholyte pH on current density was more significant at an applied voltage of 600 mV than at 850 mV. The highest hydrogen production rate was obtained at 850 mV, pH 5 amounting to 200 cm³_stp/l_anode/day (coulombic efficiency 60%, cathodic hydrogen recovery 45%, H₂ yield 1.1 mol/mol acetate converted and a COD reduction of 30.5%). Within the range (18.5–49.4 °C) of temperatures tested, 30 °C was found to be optimal for hydrogen production in the system tested, with the performance of the reactor being reduced at higher temperatures. These results show that an optimum temperature (approximately 30 °C) exists for MEC and that lower pH in the cathode chamber improves hydrogen production and may be needed if potentials applied to MECs are to be minimised.     

Effect of composition on the reactivity of Al-rich alloys with water

Fe-bearing Al–Ga–In–Sn alloys were prepared by using arc melting under high purity argon atmosphere. Their microstructures were investigated by means of XRD, SEM/EDX, and the eutectic reaction of Al with grain boundary phase Ga–In–Sn (GIS) was measured using DSC. Fe dendrites were found to present on columnar Al grain surfaces. As the amount of low melting point metals (Ga, In and Sn) is 6 wt.% with a ratio of In:Sn of 15:7, these alloys just consist of Al(Ga) and In₃Sn two phases. InSn₄ was found in an alloy as its weight ratio of In:Sn approaches 1:1 with an extra addition of Sn (1 wt.%). The reactions of Al alloys with water were performed at different water temperatures ranging from 0.5 to 50 °C. Al reacted with water at a lower water temperature of 0.5 °C, but the reaction suspended within tens of minutes. Once water was heated to a higher temperature of about 15 °C, Al reacted with water again. The H₂ generation rates measured at a water temperature of 50 °C depend on the compositions of alloys. Reasons concerning the reactivity of Al–water at different temperatures are discussed.     

Syngas production at intermediate temperature through H2O and CO2 electrolysis with a Cu-based solid oxide electrolyzer cell

Solid Oxide Electrolyzer Cells (SOECs) are promising energy devices for the production of syngas (H₂/CO) by H₂O and/or CO₂ electrolysis. Here we developed a Cu–Ce_0.9Gd_0.1O_2−δ/Ce_0.8Gd_0.2O_2−δ/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ-Ce_0.8Gd_0.2O_2−δ cell and performed H₂O and CO₂ electrolysis experiments in the intermediate temperature range (600°C–700 °C). As a baseline, the cell was first tested in fuel cell operation mode; the sample shows a maximum power density peak of 104 mW cm⁻² at 700 °C under pure hydrogen and air. H₂O electrolysis testing revealed a steady production of hydrogen with a Faraday's efficiency of 32% at 700 °C at an imposed current density of −78 mA cm⁻². CO production was observed during CO₂ electrolysis but higher cell voltages were required. A lower efficiency of about 4% was obtained at 700 °C at an imposed current density of −660 mA cm⁻². These results confirm that syngas production is feasible by water and carbon dioxide electrolysis but further improvements from both the manufacturing and the electrocatalytic aspects are needed to reach higher yields and efficiencies.     

Thermally nitrided Cu–5.3Cr alloy for application as metallic separators in PEMFCs

Cr-nitride which offers good electrical conductivity and corrosion resistance was formed on the surface of Cu–5.3 (wt.%)Cr alloy and its characteristic properties including electrochemical behavior and electrical conductivity were evaluated. The sample was annealed for 12 h in a temperature range of 600–1000 °C in a nitrogen atmosphere. Nitridation of Cr in Cu–5.3Cr alloy occurred at about 600 °C and followed Cr → Cr₂N → CrN phase transformation sequence. A continuous Cr-nitride was formed at 1000 °C, but not below 900 °C. Corrosion behavior of the continuously nitrided sample was investigated in simulated PEMFC environments. Corrosion resistance of the nitrided sample was improved in an anode environment, but not in a cathode environment. This was attributed to the dissolution of Cu through pin-hole defects on the surface of the nitrided sample just in the cathode environment. Interfacial contact resistance of the nitrided Cu–5.3Cr alloy was satisfied the target value. Furthermore, there was no recession of electrical conductivity after polarization.     

Gadolinium doped ceria-impregnated nickel-yttria stabilised zirconia cathode for solid oxide electrolysis cell

Steam electrolysis (H₂O → H₂ + 0.5O₂) was investigated in solid oxide electrolysis cells (SOECs). The electrochemical performance of GDC-impregnated Ni-YSZ and 0.5% wt Rh-GDC-impregnated Ni-YSZ was compared to a composite Ni-YSZ and Ni-GDC electrode using a three-electrode set-up. The electrocatalytic activity in electrolysis mode of the Ni-YSZ electrode was enhanced by GDC impregnation. The Rh-GDC-impregnated Ni-YSZ exhibited significantly improved performance, and the electrode exhibited comparable performance between the SOEC and SOFC modes, close to the performance of the composite Ni-GDC electrode. The performance and durability of a single cell GDC-impregnated Ni-YSZ/YSZ/LSM-YSZ with an H₂ electrode support were investigated. The cell performance increased with increasing temperature (700 °C-800 °C) and exhibited comparable performance with variation of the steam-to-hydrogen ratio (50/50 to 90/10). The durability in the electrolysis mode of the Ni-YSZ/YSZ/LSM-YSZ cell was also significantly improved by the GDC impregnation (200 h, 0.1 A/cm², 800 °C, H₂O/H₂ = 70/30).     

Conceptual design and simulation study for the production of hydrogen in coal gasification system

The conceptual design of a coal gasification system for the production of hydrogen is undertaken here using the PRO-II Simulation program. The operating conditions for the gasifier were tuned to between 1200 °C–1500 °C, 15 atm–30 atm and to a feed molar ratio of C:H₂O:O₂ = 1:0.5–1:0.25–0.5. The refinery temperature and pressure were kept at 550 °Cand 24.5 atm. The syngas produced goes to water gas shift (WGS) reactors operated at 400 °C, 24 atm (HTS) and 250 °C, 23.5 atm (LTS). The production of hydrogen was found to be independent of the concentration of steam in the feed. However, when other operating conditions are constant, the hydrogen output changes dramatically with changes to the concentration of O₂ in the feed. The optimal operating conditions for the production of hydrogen by the gasification of Drayton coal were found to be: 1500 °C, 25 atm and a feed ratio C:H₂O:O₂ = 1:0.58:0.43.