Production & Supply Chain

The capacity of each component in an off-grid water electrolyzer hydrogen production plant integrated with solar photovoltaics and a battery energy storage system represents a significant factor affecting the viability and reliability of the system. This paper describes a novel method that optimizes simultaneously the component capacities and finite-state machine based control of the system to minimize the cost of green hydrogen production. The components and control in the system are referenced to a proton exchange membrane water electrolyzer stack with a fixed nominal power of 4.5 kW. The end results are thus scalable by changing the nominal power of the electrolyzer. Simulations are carried out based on data collected from a residential solar photovoltaic installation with 300 s time resolution. Optimization of the system is performed with particle swarm optimization algorithm. A sensitivity analysis performed over the prices of the different components reveals that the price of the water electrolyzer has the greatest impact on the green hydrogen production cost. It is found that the price of the battery has to be below 0.3 e/Wh to become a feasible solution as overnight energy storage.

Climate change and global warming as well as growing global demand for hydrocarbons in industrial sectors make great incentives to investigate the utilization of CO₂ for hydrocarbons production. Therefore finding an in-depth understanding of the CO₂ hydrogenation reactors along with simulating reactor responses to different operating conditions are of paramount importance. However the reaction mechanisms for CO₂ hydrogenation and their corresponding kinetic parameters have been disputable yet. In this regard considering the previously proposed Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism which considered CO₂ hydrogenation as a combination of reverse water gas shift (RWGS) and Fischer-Tropsch (FT) reactions and using a one-dimensional pseudo-homogeneous non-isothermal model kinetic parameters of the rate expressions are estimated via fitting experimental and modelling data through a novel swarm intelligence optimization technique called dragonfly algorithm (DA). The predicted reactants conversion using DA algorithm are closer to the experimental data (with about 4% error) comparing to those obtained by the artificial bee colony (ABC) algorithm and are in significant agreement with available literature data. The proposed model is used to assess the effect of reactor configuration on the performance and temperature fluctuations. Results show that axial flow spherical reactor (AFSR) and radial flow spherical reactor (RFSR) exhibiting the same surface area with that of the cylindrical reactor (CR) i.e. AFSR-2 and RFSR-2-i are the most efficient exhibiting hydrocarbons selectivity of 40.330% and 40.286% at CO₂ conversion of 53.763% and 53.891%. In addition it is revealed that the location of the jacket has an essential role in controlling the reactor temperature.

Ni₃S₂ and NiS supported on carbon spheres are successfully synthesized by a facile hydrothermal method. And then a series of physical characterizations included XRD (X-ray diffraction) EDS (energy dispersive spectroscopy) FESEM (field emission scanning electron microscopy) and XPS (X-ray photo-electron spectroscopy) were used to analyze the samples. XRD was used to confirm that NiNi₃S₂ S2 and NiS were successfully fabricated. FESEM indicated that Ni₃S₂ and NiS disperse well on carbon spheres. Electrochemical tests showed that nickel sulfides supported by carbon spheres exhibited excellent hydrogen evolution performance. The excellent catalytic activity is attributed to the synergistic effect of carbon spheres and transition metal sulfides of which the carbon spheres act to enhance the electrical conductivity and the dispersion of Ni₃S₂ and NiS thus providing more active sites for the hydrogen evolution reaction.

A new spinelized Ni catalyst (Ni-UGSO) using Ni(NO₃)₂·6H₂O as the Ni precursor was prepared according to a less material intensive protocol. The support of this catalyst is a negative-value mining residue UpGraded Slag Oxide (UGSO) produced from a TiO2 slag production unit. Applied to dry reforming of methane (DRM) at atmospheric pressure T = 810 °C space velocity of 3400 mL/(h·g) and molar CO₂/CH₄ = 1.2 Ni-UGSO gives a stable over 168 h time-on-stream methane conversion of 92%. In this DRM reaction optimization study: (1) the best performance is obtained with the 10–13 wt% Ni load; (2) the Ni-UGSO catalysts obtained from two different batches of UGSO demonstrated equivalent performances despite their slight differences in composition; (3) the sulfur-poisoning resistance study shows that at up to 5.5 ppm no Ni-UGSO deactivation is observed. In steam reforming of methane (SRM) Ni-UGSO was tested at 900 °C and a molar ratio of H₂O/CH₄ = 1.7. In this experimental range CH4 conversion rapidly reached 98% and remained stable over 168 h time-on-stream (TOS). The same stability is observed for H₂ and CO yields at around 92% and 91% respectively while H₂/CO was close to 3. In mixed (dry and steam) methane reforming using a ratio of H₂O/CH₄ = 0.15 and CO2/CH4 = 0.97 for 74 h and three reaction temperature levels (828 °C 847 °C and 896 °C) CH₄ conversion remains stable; 80% at 828 °C (26 h) 85% at 847 °C (24 h) and 95% at 896 °C (24 h). All gaseous streams have been analyzed by gas chromatography. Both fresh and used catalysts are analyzed by scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-EDXS) X-ray diffraction (XRD) and thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS) and BET Specific surface. In the reducing environment of reforming such catalytic activity is mainly attributed to (a) alloys such as FeNi FeNi3 and Fe3Ni2 (reduction of NiFe2O4 FeNiAlO4) and (b) to the solid solution NiO-MgO. The latter is characterized by a molecular distribution of the catalytically active Ni phase while offering an environment that prevents C deposition due to its alkalinity.

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Proton conducting SmNiO₃ (SNO) thin films were grown on (001) LaAlO₃ substrates for systematically investigating the proton transport properties. X-ray Diffraction and Atomic Force Microscopy studies reveal that the as-grown SNO thin films have good single crystallinity and smooth surface morphology. The electrical conductivity measurements in air indicate a peak at 473 K in the temperature dependence of the resistance of the SNO films probably due to oxygen loss on heating. A Metal-Insulator-Transition occurs at 373 K for the films after annealing at 873 K in air. In a hydrogen atmosphere (3% H2/97% N₂) an anomalous peak in the resistance is found at 685 K on the first heating cycle. Electrochemical Impedance Spectroscopy studies as a function of temperature indicate that the SNO films have a high ionic conductivity (0.030 S/cm at 773 K) in a hydrogen atmosphere. The activation energy for proton conductivity was determined to be 0.23 eV at 473–773 K and 0.37 eV at 773–973 K respectively. These findings demonstrate that SNO thin films have good proton conductivity and are good candidate electrolytes for low temperature proton-conducting Solid Oxide Fuel Cells.

This paper reviews the progress in applying the plasma-driven solution electrolysis (PDSE) which is also referred to as the contact glow-discharge electrolysis (CGDE) or plasma electrolysis for hydrogen production. The physicochemical processes responsible for the formation of PDSE and effects occurring at the discharge electrode in the cathodic and anodic regimes of the PDSE operation are described. The influence of the PDSE process parameters especially the discharge polarity magnitude of the applied voltage type and concentration of the typical electrolytic solutions (K2CO3 Na2CO3 KOH NaOH H2SO4 ) presence of organic additives (CH3OH C2H5OH CH3COOH) temperature of the electrolytic solution the active length and immersion depth of the discharge electrode into the electrolytic solution on the energy efficiency (%) energy yield (g(H2 )/kWh) and hydrogen production rate (g(H2 )/h) is presented and discussed. This analysis showed that in the cathodic regime of PDSE the hydrogen production rate is 33.3 times higher than that in the anodic regime of PDSE whereas the Faradaic and energy efficiencies are 11 and 12.5 times greater respectively than that in the anodic one. It also revealed the energy yield of hydrogen production in the cathodic regime of PDSE in the methanol–water mixture as the electrolytic solution is 3.9 times greater compared to that of the alkaline electrolysis 4.1 times greater compared to the polymer electrolyte membrane electrolysis 2.8 times greater compared to the solid oxide electrolysis 1.75 times greater than that obtained in the microwave (2.45 GHz) plasma and 5.8% greater compared to natural gas steam reforming.

Decarbonizing the planet is one of the major goals that countries around the world have set for 2050 to mitigate the effects of climate change. To achieve these goals green hydrogen that can be produced from the electrolysis of water is an important key solution to tackle global decarbonization. Consequently in recent years there is an increase in interest towards green hydrogen production through the electrolysis process for large-scale implementation of renewable energy based power plants and other industrial and transportation applications. The main objective of this study was to provide a comprehensive review of various green hydrogen production technologies especially on water electrolysis. In this review various water electrolysis technologies and their techno-commercial prospects including hydrogen production cost along with recent developments in electrode materials and their challenges were summarized. Further some of the most successful results also were described. Moreover this review aims to identify the gaps in water electrolysis research and development towards the techno-commercial perspective. In addition some of the commercial electrolyzer performances and their limitations also were described along with possible solutions for cost-effective hydrogen production Finally we outlined our ideas and possible solutions for driving cost-effective green hydrogen production for commercial applications. This information will provide future research directions and a road map for the development/implementation of commercially viable green hydrogen projects.

Automobile exhaust heat recovery is considered to be an effective means to enhance fuel utilization. The catalytic production of hydrogen by methanol steam reforming is an attractive option for onboard mobile applications due to its many advantages. However the reformers of conventional packed bed type suffer from axial temperature gradients and cold spots resulting from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. A novel rib microreactor was designed for the hydrogen production from methanol steam reforming heated by automobile exhaust and the effect of inlet exhaust and methanol steam on reactor performance was numerically analyzed in detail with computational fluid dynamics. The results showed that the best operating parameters were the counter flow water-to-alcohol (W/A) of 1.3 exhaust inlet velocity of 1.1 m/s and exhaust inlet temperature of 773 K when the inlet velocity and inlet temperature of the reactant were 0.1 m/s and 493 K respectively. At this condition a methanol conversion of 99.4% and thermal efficiency of 28% were achieved together with a hydrogen content of 69.6%.

This paper reports on an experimental evaluation of the hydrogen separation performance in a proton exchange membrane system with Pt-Co/C as the anode electrocatalyst. The recovery of hydrogen from H2/CO2 H2/CH4 and H2/NH3 gas mixtures were determined in the temperature range of 100–160 ◦C. The effects of both the impurity concentration and cell temperature on the separation performance of the cell and membrane were further examined. The electrochemical properties and performance of the cell were determined by means of polarization curves limiting current density open-circuit voltage hydrogen permeability hydrogen selectivity hydrogen purity and cell efficiencies (current voltage and power efficiencies) as performance parameters. High purity hydrogen (>99.9%) was obtained from a low purity feed (20% H2 ) after hydrogen was separated from H2/CH4 mixtures. Hydrogen purities of 98–99.5% and 96–99.5% were achieved for 10% and 50% CO2 in the feed respectively. Moreover the use of proton exchange membranes for electrochemical hydrogen separation was unsuccessful in separating hydrogen-rich streams containing NH3 ; the membrane underwent irreversible damage.