Hydrogen Conversion Research Articles

Artificial Neural Network Modeling in the Presence of Uncertainty for Predicting Hydrogenation Degree in Continuous Nitrile Butadiene Rubber Processing

The transition from batch to continuous production in the catalytic hydrogenation of nitrile butadiene rubber (NBR) into hydrogenated NBR (HNBR) marks a significant advance for applications under demanding conditions. This study introduces a continuous process utilizing a static mixer (SM) reactor, which notably achieves a hydrogenation conversion rate exceeding 97%. We thoroughly review a mechanistic model of the SM reactor to elucidate the internal dynamics governing the hydrogenation process and address the inherent uncertainties in key parameters such as the Peclet number (Pe), dimensionless time (θτ), reaction coefficient (R), and flow rate coefficient (q). A comprehensive dataset generated from varied parameter values serves as the basis for training an artificial neural network (ANN), which is then compared against traditional models including linear regression, decision tree, and random forest in terms of efficacy. Our results clearly demonstrate the ANN’s superiority in predicting the degree of hydrogenation, achieving the lowest root mean squared error (RMSE) of 3.69 compared to 21.90 for linear regression, 4.94 for decision tree, and 7.51 for random forest. The ANN’s robust capability for modeling complex nonlinear relationships and dynamics significantly enhances decision-making, planning, and optimization of the reactor, reducing computational demands and operational costs. In other words, this approach allows users to rely on a single ML-based model instead of multiple mechanistic models for reflecting the effects of possible uncertainties. Additionally, a feature importance study validates the critical impact of time and element number on the hydrogenation process, further supporting the ANN’s predictive accuracy. These findings underscore the potential of ML-based models in streamlining and enhancing the efficiency of chemical production processes.

Nanotechnology's potential in advancing renewable energy solutions

Nanotechnology has emerged as a promising frontier in the quest for sustainable energy solutions, offering transformative opportunities to address pressing challenges in renewable energy generation, storage, and conversion. This review explores the potential of nanotechnology in advancing renewable energy solutions, encompassing a wide range of applications spanning solar energy, wind energy, energy storage, and fuel cells. By leveraging the unique properties of nanomaterials, such as high surface area-to-volume ratio, tunable optical and electronic properties, and enhanced catalytic activity, researchers and engineers can develop innovative materials and devices with unprecedented performance and efficiency. Nanotechnology-enabled advancements in solar photovoltaics include the development of next-generation solar cells incorporating nanostructured materials, such as quantum dots, nanowires, and perovskite-based solar cells, to enhance light absorption, charge transport, and overall power conversion efficiency. In the realm of energy storage, nanomaterials hold promise for improving the performance and longevity of batteries, supercapacitors, and other energy storage devices through enhanced electrode materials, electrolytes, and nanostructured architectures. Furthermore, nanotechnology-driven innovations in wind energy, such as lightweight and durable nanocomposite materials for turbine blades, and advancements in fuel cell technologies, including catalyst nanoparticles for efficient hydrogen production and conversion, exemplify the diverse applications and transformative potential of nanotechnology in renewable energy. Through a comprehensive analysis of recent research and development efforts, this abstract underscores the critical role of nanotechnology in accelerating the transition to a sustainable and renewable energy future. Keywords: Nanotechnology, Renewable Energy, Solar Energy, Wind Energy, Energy Storage, Nanomaterials.

A Study on the Hydro-Liquefaction Kinetics of Shengli Lignite during the Heating-Up and Isothermal Stages under Mild Conditions

Studying the hydro-liquefaction kinetics of lignite contributes to optimizing the mild liquefaction process for lignite. In this paper, the direct liquefaction performance of Shengli lignite (SL) was investigated using a H2/THN system with 4 MPa of initial pressure, and reaction kinetic models were established for the heating-up stage and the isothermal stage. The result showed that the liquefaction performance of the SL was excellent, with a conversion of 62.18% and an oil and gas (O + G) yield of 29.88% at 698.15 K. After one hour of reaction, the conversion and O + G yield were 94.61% and 76.78%, respectively. During the heating-up stage, the easily reactive part of the SL was 50.07%, and it was converted directly into oil, gas, asphaltene (AS), and preasphaltene (PA) simultaneously. There was no significant secondary hydrogenation conversion of the AS and PA products. During the isothermal stage, the hard-to-react part was predominantly converted into AS and PA, while the remaining easily reactive part continue to react completely. The conversion of AS and PA into oil and gas was a rate-controlling step during this stage. The amount of unreacted coal estimated using the model calculated in the isothermal stage was 2.98%, which was significantly consistent with the experimental value of 2.81%.

Development of a research cryostat for direct thermoacoustic cooling and conversion of hydrogen

Hydrogen thermoacoustics is a relatively unexplored but promising topic for development of new cryocoolers and hydrogen liquefaction. This paper describes a new research cryostat designed to investigate hydrogen as a working fluid in thermoacoustic systems. The cryostat is a modular, turbo-molecular pump driven, vacuum chamber with a 4.2 K pulse-tube cryocooler capable of 45 W of cooling at 50 K. Using this cryostat, a feasibility study of direct thermoacoustic cooling with ortho-parahydrogen conversion is initiated. An acoustic resonator system is designed to have the fundamental acoustic mode excited via imposed temperature gradient in a porous stack between the ambient environment and cold bar connected to the cryocooler. The generated acoustic waves transfer heat inside another porous stack to produce a refrigeration effect at cryogenic temperatures. In addition, the regenerator solid matrix will be catalyzed for ortho-parahydrogen conversion to demonstrate a novel combination of cooling and conversion of cryogenic hydrogen in a single device. Design, construction, and performance of the cryostat and modelling results for one thermoacoustic system are reported.

Numerical analysis of transport phenomena in a steam reforming reactor with optimal multi-segments catalyst distribution

The contemporary industrial trends pursue alternative energy sources, to substitute fossil fuels. The current direction is induced by concerns regarding exhausting natural resources and the environmental impact of the technologies rising globally. Conventional technologies have a dominant share of the current energy market. The most crucial issue with current technology is the emission of greenhouse gases and their negative impact on climate. One of the possible approaches to limit the issue of emissions is the steam reforming of natural gas, leading to the production of hydrogen. Fuel cells are a robust technology, able to conduct a catalytic conversion of hydrogen and oxygen, for the direct production of electrical energy. Fuel cells are one of the most environment-friendly technologies to this day, as their exhaust gases mostly consist of steam. Currently, almost 50% of the hydrogen produced is acquired via hydrocarbons reforming. The process described in the presented analysis occurs between methane and steam. The presented numerical analysis regards small-scale reactors, which are more suitable when it comes to the processing of distributed or stranded resources for hydrogen production To optimize the small-scale unit’s performance, the macro-patterning strategy is introduced. Steam reforming has a strong endothermic character and tends to produce unfavorable thermal conditions. The process enhancement is acquired by introducing non-catalytic regions to the catalytic insert geometry. The non-catalytic segments are introduced to suppress the reaction locally, decreasing the magnitude of temperature gradients. Unification of the temperature distribution is proven to increase the reforming’s effectiveness. The presented analysis introduces a new approach to the catalytic insert division, to investigate if a complete temperature field unification is possible. The catalytic insert is simultaneously divided along the reactor’s radius and length, resulting in a set of concentric rings, placed along the reactor’s axis. The calculations are conducted using in-house numerical procedure, coupled with a genetic algorithm. The algorithm optimizes the process effectiveness by modification of the segment’s alignment and porosity.

Research on matching supply of power and cold energy of liquid hydrogen cold chain logistics vehicles

Liquid hydrogen cold-chain logistics vehicle (LHCCLV) is a special vehicle using liquid hydrogen (LH2) as the source of both power and cold energy. A significant weakness of LH2 is its high energy consumption during the hydrogen liquefaction process, thus the utilization of cold energy in LHCCLV can improve the economic performance and competitiveness of LH2. Because of the high energy storage density of LH2 and the relatively high efficiency of fuel cells, we find that cold energy can not meet the demand of LHCCLV. Therefore, we consider enlarging the cold energy by efforts including the para-ortho hydrogen conversion (POC), whose reverse reaction consumes an energy level exceeding 20% during the hydrogen liquefaction process. In this paper, numerical models of discharging hydrogen from the LH2 and subcooling hydrogen tank are established, and the influence of POC and other efforts on the supply of cold energy is analyzed. The changes in instantaneous and total cold energy supply under different working conditions are analyzed, and the important influence of POC and other efforts is confirmed. The beneficial effect of POC is quantified in the paper, especially for the cold energy supply. This paper provides an essential reference for the research and development of LHCCLV. Also, it guides the comprehensive utilization of cold energy in other situations to promote the improvement of the economy of hydrogen energy utilization routes in the form of LH2.

Materials for green hydrogen production, storage, and conversion

Materials for green hydrogen production, storage, and conversion

Experimental study and modeling of the liquid phase hydrogenation of acetylene

Selective hydrogenation of acetylene is an important process for both ethylene purification and ethylene production from acetylene in the industry. Herein, we proposed liquid phase acetylene hydrogenation for high feed concentrations of C2H2 (8 %) and CO (20 %), which is used to produce ethylene as a subsequent process of partial oxidation of natural gas. The experiments were carried out in a stirred tank reactor using N-methylpyrrolidone (NMP) as solvent and PdAg/SiO2 as catalyst. The liquid phase process obtained a much higher selectivity to ethylene (92 %) with only 8 % selectivity to green oil (GO) and C4, compared to 71 % ethylene selectivity in gas phase hydrogenation. Furthermore, in the liquid phase ethylene selectivity increased with increasing acetylene conversion, especially in the conversion range of 80–100 %. We developed a model incorporating reaction kinetics, mass transfer and reactor model to predict the acetylene conversion and ethylene selectivity in liquid phase hydrogenation. The calculation results indicated that hydrogenation in the liquid phase operated at a lower acetylene concentration and a higher H2/C2H2 ratio, especially under high acetylene conversions. This explains why the liquid phase hydrogenation of acetylene has a much higher selectivity to ethylene than the gas phase process.

On the validation and applicability of multiphysics models for hydrogen SOFC

Solid oxide fuel cells (SOFC) are a viable alternative for environmentally-friendly conversion of hydrogen into energy and multiphysics simulation can be used to diminish the experimental effort to improve their efficiency. However, an appropriate model of the involved processes and their parameters must be chosen. This paper studies the effects of choice between Maxwell–Stefan and Fick’s law models, and uncertainty of electrode ionic conductivity σion and anodic reference exchange current density i0,ref,f, on cell performance as implemented in the COMSOL Multiphysics® software. In the case of Maxwell–Stefan, peak average power output increased by 21.9% as σion varies from 10−3 to 10−1 S/cm, while the model based on Fick’s law shows an increase of 55.2%. The Maxwell–Stefan model exhibits an increase in peak power of 6% as i0,ref,f ranges from 0.4 to 0.8 A/cm2, and the Fick’s law model an increase of 8.2%. The dependence of the Maxwell–Stefan model on σion is characterized as logarithmic in the studied range. The Maxwell–Stefan model is deemed preferable because its lower sensitivity to the studied parameters helps mitigate uncertainty. It is concluded that despite its limitations, multiphysics modeling is a useful tool for directing research on SOFC materials owing to its descriptive potential.

Accelerating bulk proton transfer in Sr2Fe1.5Mo0.5O6-δ perovskite oxide for efficient oxygen electrode in protonic ceramic electrolysis cells

Protonic ceramic electrolysis cells (PCECs) have attracted significant attention as a promising technology for green hydrogen production and conversion. However, traditional PCECs oxygen electrodes exhibit poor electrochemical performance because of their limited hydration ability and lack of intrinsic protonic conductivity. In this study, a W-doped perovskite oxide, Sr2Fe1.5Mo0.4W0.1O6-δ (SFMW), with a strong hydration capacity and an accelerated proton mobility, was designed to serve as the oxygen electrode in PCECs. The results indicate that W doping enhances the concentration of oxygen vacancies in Sr2Fe1.5Mo0.5O6-δ (SFM) and facilitates the adsorption of H2O onto the oxygen electrode, thereby significantly accelerating proton mobility. The bulk diffusion coefficient of protons (DH) in SFMW, estimated through electrical conductivity relaxation measurement, can reach up to 2.86 × 10−5 cm∙s−1 at 750 °C, which is significantly higher than that of SFM (7.96 × 10−6 cm∙s−1). Consequently, SFMW exhibited impressive electrochemical performance, as evidenced by its lower polarization resistance (0.072 Ω⋅cm2, 700 °C in air) and higher current density (945 mA/cm2 with a voltage of 1.3 V at 650 °C) in PCECs. These results suggest that accelerating bulk proton transfer by W doping is highly feasible and holds great potential for the development of oxygen electrodes for high-activity PCECs.

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

Solar-Powered AEM Electrolyzer via PGM-Free (Oxy)hydroxide Anode with Solar to Hydrogen Conversion Efficiency of 12.44.

Water electrolyzers powered by renewable energy are emerging as clean and sustainable technology for producing hydrogen without carbon emissions. Specifically, anion exchange membrane (AEM) electrolyzers utilizing non-platinum group metal (non-PGM) catalysts have garnered attention as a cost-effective method for hydrogen production, especially when integrated with solar cells. Nonetheless, the progress of such integrated systems is hindered by inadequate water electrolysis efficiency, primarily caused by poor oxygen evolution reaction (OER) electrodes. To address this issue, a NiFeCo─OOH has developed as an OER electrocatalyst and successfully demonstrated its efficacy in an AEM electrolyzer, which is powered by renewable electricity and integrated with a silicon solar cell.

Hydrogen generation by hydrolysis of Sc–Sn alloy over a wide temperature range as low as 0 °C

A series of Sc–Sn alloys are prepared by the arc-melting method and their hydrogen generation performance of hydrolysis in pure water is investigated. It was found that only Sc element reacts with water in Sc–Sn alloy, while Sn element is retained as an elemental metal. The reaction temperature of Sc with water can be reduced below 0 °C after Sc and Sn are alloyed. The Sc3Sn2 alloy has the best hydrogen generation performance. Its hydrogen conversion rate is up to 90% at 0 °C for 100 min as well as when the water temperature dropped from 60 °C to 0 °C, the average conversion rate in the first 30 min only dropped from 19.95 mL/min∙g to 14.31 mL/min∙g. The hydrogen generation performance of Sc–Sn alloys depends on the reaction activity after Sc and Sn alloying, the effect of micro galvanic cells and the solidification microstructure in the alloy ingot.

Novel flame-retardant aluminum-based hydrolyzed material

Al is the most abundant metallic element in the Earth's crust, and its theoretical capacity of hydrolyzing hydrogen production is high (1244mL/g). How to destroy Al2O3 films and control reaction rate are the key to control hydrolysis. Herein, we designed an activity-controlled and flame-retardant Al based hydrolytic composite by analyzing the mechanism of Al2O3 film breaking. The results show that the addition of anion is an important factor to improve film breaking. Among them, the system with CaH2 and NaF showed the best modification effect in deionized water (vmax = 265 mL/(s·g), Cmax = 1075 mL/g), and the mean hydrogen conversion was 97.79%. It is generally believed that the synergistic pitting effect of H− and F− is the heart of the continuation of the hydrolysis reaction. However, by studying the mechanism of pitting, we noticed that Ca(OH)2, Al(OH)3 and F− can provide an in-situ high concentration alkali field, which plays the crucial role for hydrolysis of Al. Meanwhile, the ignition test of the composite material shows that it is flame retardant. Then, the proposed novel hydrolysis film breaking mechanism of in-situ high concentration alkali field can also provide an idea for the further development of hydrolyzed hydrogen production materials.

What Metals Should Be Used to Mediate Electrosynthesis of Ammonia from Nitrogen and Hydrogen from a Thermodynamic Standpoint?

Recently, metal-mediated electrochemical conversion of nitrogen and hydrogen to ammonia (M-eNRRs) has been attracting intense research attention as a potential route for ammonia synthesis under ambient conditions. However, which metals should be used to mediate M-eNRRs remains unanswered. This work provides an extensive comparison of the energy consumption in the classical Haber Bosch (H-B) process and the M-eNRRs. The results indicate that when employing lithium and calcium, metals popularly used to mediate the M-eNRRs, the energy consumption is more than 10 times greater than that of the H-B process even assuming a 100% Faradaic efficiency and zero overpotentials. Only electrosynthesis with a cell voltage not exceeding 0.38 V might have the potential to rival the H-B process from an energetic perspective. A further analysis of other metals in the periodic table reveals that only some heavy metals, including In, Tl, Co, Ni, Ga, Mo, Sn, Pb, Fe, W, Ge, Re, Bi, Cu, Po, Tc, Ru, Rh, Ag, Hg, Pd, Ir, Pt, and Au, can potentially consume less energy than that of the H-B process purely from a thermodynamic standpoint, but whether they can activate N2 under ambient conditions is yet to be explored. This work shows the importance of performing thermodynamic analysis for the development of an innovative strategy to synthesize ammonia with the ultimate goal of replacing the H-B process on a large scale.

Z-scheme ZnCdS/NiCo-LDH photocatalyst followed dual-channel charge transfer via Au-intercalation for renewable hydrogen production

Exploration of effective and renewable photocatalysts is essential for solar to hydrogen conversion technologies. However, the application of some photocatalysts with great potential, such as ZnCdS, are seriously limited by the sluggish charge transfer/separation and unavoidable light corrosion. In this work, Au/ZnCdS/NiCo-LDH ternary heterojunction was constructed by introducing Au nanoparticle mediator in core-shell ZnCdS/NiCo-LDH, which exhibits an enhanced H2 production rate of 4.89 mmol g−1 h−1 under visible light irradiation and unexpected recyclability with 6.2 % rate reduction after 15 consecutive cycles. The enhanced photocatalytic performance is attributed to the dual pathways (Z-scheme and localized surface plasmon resonance) enabled in Au/ZnCdS/NiCo-LDH, which improves the separation of photo-generated carriers, accelerates the electron transport, and provides active sites for photocatalytic oxidation. This work provides a promising technology to jointly improve photocatalytic activity and stability by modulating the interfacial carrier dynamics of photocatalysts.

Experimental Study on Catalytic Conversion of Ortho and Para Hydrogen

Experimental Study on Catalytic Conversion of Ortho and Para Hydrogen

Hydrogen Production from Rice Husk: Techno-Economic and Life Cycle Analysis

The abundance of rice husk in some regions of Southeast Asia makes it a potential feedstock for hydrogen synthesis. However, the information on economic and environmental feasibility of its conversion to hydrogen is lacking. This study aims to assess the techno-economic and life cycle sustainability of hydrogen production from rice husk via the thermochemical gasification method. The techno-economic analyses reveal that rice husk-based hydrogen conversion is more financially attractive than conventional hydrogen production technology. The results of the life cycle assessment are also promising, especially with the global warming potential of the rice husk-based hydrogen production being 99.7 % lower than that of natural gas steam reforming. Waste valorization of rice husk into hydrogen is therefore economically and environmentally viable.

Bifunctional Mo4O11 Nanosheets-Engineered Co-Ni alloy nanowires enable High-Efficiency seawater electrolysis and Zn-Seawater battery

This study reports an electrocatalyst derived from multi-valent Mo4O11 nanosheets coupled Co-Ni (CN) nanowires (NW) (denoted as CN@Mo4O11) with improved catalytic coherency for both high-performance seawater splitting and Zn-seawater battery. The CN@Mo4O11 material significantly enhances the catalytical activity with a low overpotential of 63 mV/69 mV for hydrogen evolution and 100 mV/120 mV for oxygen evolution, respectively, to attain 10 mA⋅cm−2 in alkaline freshwater/seawater. An electrolyzer cell of CN@Mo4O11(+,-) exhibits a low cell voltage of 1.40 V/1.44 V at 10 mA‧cm−2 during alkaline freshwater/seawater splitting with an excellent performance retention of 98.6 %/97.6 % after a long-term operation for 50 h. The solar cell coupled electrolyzer also delivers a high solar to hydrogen conversion efficiency of 15.54 %/16.1 % in alkaline freshwater/seawater. A Zn-seawater battery based on CN@Mo4O11 cathode also delivers high current and power densities of 82 mA‧cm−2 and 27.6 mW‧cm−2, respectively, with a stable discharge time of 40 h. The CN@Mo4O11 heterostructure imparts favorable density of states and optimized adsorption energy for HER and OER, as deduced from DFT calculations, leading to improved overall catalytic performance and corrosion resistance in seawater. Results of this work clearly prove that this proposed catalyst architecture indeed has a huge potential for both seawater splitting and Zn-seawater battery fabrication.

Performance Analysis of Waste Biomass Gasification and Renewable Hydrogen Production by Neural Network Algorithm

Abstract This study assesses renewable hydrogen production via gasification of residual biomass, using artificial neural networks (ANNs) for predictive modeling. The process uses residues from sugarcane and orange harvests, sewage sludge, corn byproducts, coffee remnants, eucalyptus remains, and urban waste. Simulation data from aspen plus® software predict hydrogen conversion from each biomass type, with a three-layer feedforward neural network algorithm used for model construction. The model showed high accuracy, with R2 values exceeding 0.9941 and 0.9931 in training and testing datasets, respectively. Performance metrics revealed a maximum higher heating value (HHV) of 18.1 MJ/kg for sewage sludge, the highest cold gas efficiency for urban and orange waste (82.2% and 80.6%), and the highest carbon conversion efficiency for sugarcane bagasse and orange residue (92.8% and 91.2%). Corn waste and sewage sludge yielded the highest hydrogen mole fractions (0.55 and 0.52). The system can reach relative exergy efficiencies from 24.4% for sugarcane straw residues to 42.6% for sugarcane bagasse. Rational exergy efficiencies reached from 23.7% (coffee waste) to 39.0% (sugarcane bagasse). This research highlights the potential of ANNs in forecasting hydrogen conversion and assessing the performance of gasification-based renewable hydrogen procedures using biomass wastes.