CO2-free Hydrogen Research Articles

Producing Hydrogen with Less Energy in Ammonia Electrolyzer Stack Using Pt-Ir Catalyst Dual-Layer Electrode

Electrochemical ammonia decomposition has recently been regarded as a possible future technology for CO2-free hydrogen production. Pt-based catalysts have already known for having excellent activity in ammonia oxidation reactions (AOR) due to the fast dehydrogenation step enabled by the moderate adsorption strengths of nitrogen species [1]. Among them, the incorporation of Ir into Pt notably decreases the activation energy required for ammonia oxidation on Pt, lowing onset potential in alkaline media [2]. Besides, the electrolysis of ammonia has a less energy consumption than water electrolysis because of the lower operating voltage at the Anode [3]. In this study, we fabricated dual-layer electrode containing Pt-Ir catalyst, enhancing the AOR catalytic activity and showing long-term stability. The ammonia electrolysis single-cell with an anion exchange membrane (AEM) was successfully operating and then scaled up to a large area stack cell. We observed that this electrolyzer stack cell produced high-purity hydrogen using less energy than water electrolysis.AcknowledgementsThis research was supported by National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (NRF-2021K1A4A8A01079455). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) [No. 2021R1A5A1028138].Reference[1] J. Liu, Z. Liu, Adv. Funct. Mater 2022, 32, 2110702[2] A. Estejab, G. G. Botte, Comput. Theor. Chem 2016, 1091, 31-40[3] J. Gwak, M. Choun, ChemSusChem 2016, 9, 403–408

Requirements for CO2-free hydrogen production at scale

Requirements for CO2-free hydrogen production at scale

Exploring the role of process control and catalyst design in methane catalytic decomposition: A machine learning perspective

Methane catalytic pyrolysis presents a promising avenue for producing CO2-free hydrogen. However, optimizing catalyst composition and process parameters through experimental studies has been resource-intensive. Machine learning techniques have been increasingly utilized to deepen the understanding of process mechanisms. In this study, machine learning models were developed to deepen the understanding of the effects of process control and catalyst design on CH4 conversion performance. The optimal CH4 conversion model achieved a testing R2 of 0.9999. To further assess the model's real-world applicability, an initial verification experiment was conducted using a catalyst composition and process parameters distinct from those in the dataset. The results reaffirmed the model's good accuracy in real-world scenarios. Delving deeper into the intricacies of methane pyrolysis, the Shapley values and partial dependence plots generated by the model were scrutinized and discussed to provide a new perspective on the influence of process control and catalyst design parameters on methane catalytic decomposition.

Molten salts coupled Ni/Al2O3 for hydrogen from CH4 pyrolysis at mild temperature in bubble-cap reactor

Methane pyrolysis is a promising sustainable technology for CO2-free hydrogen production. However, the development of stable methods for methane pyrolysis to produce hydrogen at lower temperatures has presented significant challenges. This study presents a reaction system that combines molten carbonate with Ni/Al2O3 catalyst and investigates methane pyrolysis using this system in a bubble-cap reactor. Remarkably, this system exhibited a low activation energy of 145.8 kJ per mole, enabling the achievement of a methane conversion of 92.5 % at 580 °C by employing a double-layer bubble cap tray configuration. Furthermore, the system showcases sustained activity for a duration of up to 72 h.

Effect of Ni/SiO2 catalyst preparation method on methane decomposition and CO2 gasification cycles

Catalytic methane decomposition is a promising reaction to produce CO2-free hydrogen from methane-rich feedstock with solid carbon as a by-product. Significant research conducted on this reaction to find ways to manage and utilize this solid carbon. In this work, the methane decomposition reaction is followed by Reverse Boudouard Reaction using CO2 feedstock to convert the solid carbon to carbon monoxide, which is a valuable starting component for many chemical applications. Realizing this promising concept would require a catalyst that is efficient for both reactions. Herein, we explored the potential of using solution combustion synthesis (SCS) to make a 5 wt% of Ni supported SiO2 catalyst and benchmarked it versus the conventional impregnation method. The catalyst prepared by SCS showed an improved performance at different temperatures, space velocities, and catalyst pellet sizes. The SCS catalyst successfully completed five repeated cycles reaching up to 38.1 h of stable time on stream operation, whereas the impregnated catalyst was not able to complete the second testing cycle with only 14 h of time on stream operation. A thorough characterization using XRD, H2 and O2 TPR, TEM, SEM, XPS, and Raman spectroscopy were conducted to provide an adequate explanation for the observed performances for both catalysts. The Ni nanoparticles size and distribution, the strength of the metal support interaction, and the nature of graphitic carbon were the key factors affecting the catalytic performance. Insights on how to make an optimal catalyst for this promising process is identified which is a step forward toward making separated H2 and CO streams from methane feedstock and CO2, respectively.

Experiment and simulation of non-catalytic thermal decomposition of CH4 for CO2-free hydrogen production in a vertical tube

To address climate change issues, there has been growing interest in low-carbon H2 production technologies with the potential for zero-CO2 emissions. Non-oxidative CH4 pyrolysis is a promising method for producing H2 and solid carbon without generating CO2 emissions. This study presents experimental and numerical studies on non-catalytic CH4 pyrolysis using a vertical tube reactor (28 mm in diameter and 1800 mm in height). A three-dimensional (3D) Eulerian computational fluid dynamics (CFD) model coupled with chemical reaction and heat transfer was developed and validated against the experimentally determined axial temperature profiles and methane conversion (XCH4). The hydrodynamics, reaction kinetics, and heat transfer characteristics were investigated using the validated CFD model. The highest XCH4 of 99% was achieved at 1200 °C with a gas flow rate of 0.5 LPM. Heat transfer combined with natural and forced convection was confirmed by the CFD simulation of the tubular reactor. The heat transfer coefficient in the reaction zone ranged from 43 to 46 W/m2/°C. The CFD simulation served as a viable tool for examining the influence of the hydrodynamics, heat transfer, and reaction kinetics on the performance of the reactor with a given geometry and under specified operating conditions in non-catalytic CH4 pyrolysis.

100 W-class green hydrogen production from ammonia at a dual-layer electrode containing a Pt-Ir catalyst for an alkaline electrolytic process

Ammonia allows storage and transport of hydrogen over long distances and is an attractive potential hydrogen carrier. Electrochemical decomposition has recently been used for the conversion of ammonia to hydrogen and is regarded as a future technology for production of CO2-free pure hydrogen. Herein, a heterostructural Pt-Ir dual-layer electrode is developed and shown to achieve successful long-term operation in an ammonia electrolyzer with an anion exchange membrane (AEM). This electrolyzer consisted of eight membrane electrode assemblies (MEAs) with a total geometric area of 200 cm2 on the anode side, which resulted in a hydrogen production rate of 25 L h−1. We observed the degradation in MEA performance attributed to changes in the anode catalyst layer during hydrogen production via ammonia electrolysis. Furthermore, we demonstrated the relationship between the ammonia oxidation reaction (AOR) and the oxygen evolution reaction (OER).

Research on the Production of Turquoise Hydrogen from Methane (CH4) through Plasma Reaction

Turquoise hydrogen is produced through a process of separating carbon into solid carbon based on fossil fuels and refers to hydrogen that does not produce carbon dioxide. In this study, the characteristics of turquoise hydrogen production through a methane thermal cracking reaction using an arc plasma torch were investigated. The plasma torch operated stably under high voltage and transport gas flow conditions. The composition of the gas generated from the methane plasma reaction was analyzed using an online IR gas analyzer and GC-FID. The experimental results show that the hydrogen yield decreased to 16.4% as the methane feed rate increased but increased to 58.8% as the plasma power increased. Under these conditions, the yield of solid carbon, a valuable byproduct, was also shown to increase to 62.9%. In addition, solid carbon showed high-temperature heat-treated characteristics based on its generation location. Carbon oxides such as CO and CO2 are rarely generated under any experimental conditions. Consequently, it can be considered that plasma thermal cracking is a promising technology for CO2-free hydrogen production and a valuable solid carbon.

CO2-Free Hydrogen Production by Methane Pyrolysis Utilizing a Portion of the Produced Hydrogen for Combustion

Air pollutants such as carbon dioxide and nitrogen oxides emitted by the combustion of fossil fuels have become the subject of increasing concern. Hydrogen has accordingly emerged as a promising low-emission alternative energy source. Among the various methods for hydrogen production, methane pyrolysis, which produces hydrogen without emitting carbon dioxide, has gained substantial attention. This study evaluated the self-sustainability of a new hydrogen production system based on methane pyrolysis, in which a portion of the hydrogen produced is used as combustion fuel rather than relying on catalysts and electrical heating. Coupled heat transfer and one-dimensional reaction simulations employing two plug-flow reactors of a counterflow double-pipe heat exchanger were conducted to investigate the feasibility and efficiency of the proposed system, as well as the influence of flow conditions on hydrogen production. The results confirmed system viability, informed the estimation of hydrogen production rates, and provided methane conversion rate data emphasizing the critical role of low-flow conditions and residence time in system efficiency. Additionally, the production of carbon constituted a significant aspect of system efficiency. These findings indicate that the proposed system can produce environmentally friendly hydrogen, contributing to its potential utilization as a sustainable energy source.

Balancing act: influence of Cu content in NiCu/C catalysts for methane decomposition.

Thermal catalytic decomposition of methane is an innovative pathway to produce CO2-free hydrogen from natural gas. We investigated the role of Cu content in carbon-supported bimetallic NiCu catalysts. A graphitic carbon material was used as a model support, and we combined operando methane decomposition experiments in a thermogravimetric analyzer with in situ electron microscopy measurements. The carbon yield was maximum with around 30% Cu in the nanoparticles. Adding more Cu drastically lowered the carbon solubility in the metal nanoparticles, which lowered the initial reaction rate and overall carbon yield. In situ TEM measurements showed that the addition of Cu to the catalysts strongly influenced the metal nanoparticle shape and size during carbon growth, and the growth mode. NiCu particles were larger, remained spherical and facilitated steady CNF growth. In contrast, pure Ni nanoparticles fluctuated in shape, sometimes fragmented, and showed stuttering CNF growth. This was ascribed to fluctuating coverage of part of the Ni nanoparticle surface with amorphous carbon, which increased the chance of total encapsulation and hence deactivation of the individual Ni nanoparticles. This supports a picture where balancing the carbon supply, transport, and nucleation of amorphous and crystalline carbon is crucial. Our results also highlight the importance of combining statistically relevant measurements with microscopic information on individual nanoparticles to understand overall catalytic trends from the combined behavior of individual catalyst nanoparticles.

Computational Design of Durable and Selective Double Atom Catalysts Toward the Electrochemical NH3 Production: Role of Carbon Defects

Electrochemical NH3 production through nitrogen reduction reaction (N2RR) has received much attention as an energy-efficient way to produce ammonia, which is one of CO2-free hydrogen carriers. Note that electrochemical N2RR is carried out under mild temperature and pressure conditions, unlike the conventional Haber-Bosch process for chemical NH3 production, which requires a lot of energy due to the high temperature and pressure conditions. In recent years, the concept of double atom catalysts (indicated DAC) has been proposed to improve the reactivity of catalyst owing to the maximized utilization and 100% dispersion of active sites. The main problems in the development of DACs are the poor stability [the dissolution of double atoms into electrolyte and agglomeration of double atoms] and the low selectivity [lower onset potential for N2RR than HER (hydrogen evolution reaction)]. In this study, by using density functional theory (DFT) calculations, we examined the role of carbon defects (di, tri, quad vacancies) in graphene in enhancing the stability and selectivity in single and double atom catalysts (Ru, RuRu, and RuFe) and screened the novel double atom catalysts which have high selectivity to NH3 and durability at reaction conditions by ligand and support engineering. First, we found the optimal carbon defect structure to suppress the dissolution and agglomeration of double atoms and unraveled the factors to enhance the selectivity to N2RR over HER. Second, we developed the multiscale model to design the selective and durable double atom catalysts by identifying the descriptors to represent the durability and selectivity of double atoms catalysts. Next, we computationally screened the novel DACs (consisting of transition metals) by using the developed multiscale model. Finally, through the electronic structure calculation, we elucidated the underlying mechanism of defect in determining the durability and selectivity of double atom catalyst. Our study can provide the design factors to efficiently engineer the carbon defect and double atom in the development of NH3 production catalyst.

Combined Methane Pyrolysis and Solid Carbon Gasification for Electrified CO2-Free Hydrogen and Syngas Production

The coupling of methane pyrolysis with the gasification of a solid carbon byproduct provides CO2-free hydrogen and hydrogen-rich syngas, eliminating the conundrum of carbon utilization. Firstly, the various types of carbon that are known to result during the pyrolysis process and their dependencies on the reaction conditions for catalytic and noncatalytic systems are summarized. The synchronization of the reactions’ kinetics is considered to be of paramount importance for efficient performance. This translates to the necessity of finding suitable reaction conditions, carbon reactivities, and catalysts that might enable control over competing reactions through the manipulation of the reaction rates. As a consequence, the reaction kinetics of methane pyrolysis is then emphasized, followed by the particularities of carbon deposition and the kinetics of carbon gasification. Given the urgency in finding suitable solutions for decarbonizing the energy sector and the limited information on the gasification of pyrolytic carbon, more research is needed and encouraged in this area. In order to provide CO2-free hydrogen production, the reaction heat should also be provided without CO2. Electrification is one of the solutions, provided that low-carbon sources are used to generate the electricity. Power-to-heat, i.e., where electricity is used for heating, represents the first step for the chemical industry.

Ternary NiMo-Bi liquid alloy catalyst for efficient hydrogen production from methane pyrolysis.

Methane pyrolysis (MP) is a potential technology for CO2-free hydrogen production that generates only solid carbon by-products. However, developing a highly efficient catalyst for stable methane pyrolysis at a moderate temperature has been challenging. We present a new and highly efficient catalyst created by modifying a Ni-Bi liquid alloy with the addition of Mo to produce a ternary NiMo-Bi liquid alloy catalyst (LAC). This catalyst exhibited a considerably low activation energy of 81.2 kilojoules per mole, which enabled MP at temperatures between 450 and 800 Celsius and a hydrogen generation efficiency of 4.05 ml per gram of nickel per minute. At 800 Celsius, the catalyst exhibited 100% H2 selectivity and 120 hours of stability.

Enhancing molten tin methane pyrolysis performance for hydrogen and carbon production in a hybrid solar/electric bubbling reactor

Methane pyrolysis in liquid metals is a worth-developing process for CO2-free hydrogen production. This study investigates methane pyrolysis in molten tin and highlights the impact of several parameters on methane conversion (XCH4) in a novel hybrid solar/electric bubbling reactor. Temperature (1200–1300 °C), total inlet gas flow rate (Q0 = 0.25–0.5 NL/min), melt height (Him = 60-120-235 mm) and hybridization are addressed. Increasing the temperature from 1200 °C to 1300 °C (Q0 = 0.25 NL/min and Him = 120 mm) improves XCH4 (32% vs. 69%). Increasing Q0 from 0.25 to 0.5 NL/min (T = 1200 °C and Him = 120 mm) reduces XCH4 (19% vs. 9%). Doubling the melt height (Him from 60 to 120 mm) increases the residence time of bubbles, which increases XCH4 (7% vs. 19%). A customized sparger is also tested and shows little effect, probably because the holes are relatively large (1 mm diameter). An immersed bed of steel particles (0.2–0.4 mm diameter) instead shows improved results (XCH4 = 32%) at a relatively low temperature (1100 °C). Continuous reactor operation at 1300 °C without clogging is also confirmed. Analysis of carbon accumulated at melt surface during molten media methane pyrolysis reveals a tin-containing sheet-like structure.

Selecting Optimal CO2-Free Hydrogen Production Technology Considering Market and Technology

Selecting Optimal CO2-Free Hydrogen Production Technology Considering Market and Technology

A semi-continuous process for co-production of CO2-free hydrogen and carbon nanotubes via methane pyrolysis

A semi-continuous process for co-production of CO2-free hydrogen and carbon nanotubes via methane pyrolysis

CO2 Hydrogenation to Methanol over a Pt-Loaded Molybdenum Suboxide Nanosheet with Abundant Surface Oxygen Vacancies

Hydrogenation of carbon dioxide (CO2) using CO2-free hydrogen (H2) to produce methanol (CH3OH) is a promising reaction that can alleviate both carbon emissions and the dependence on fossil fuels. Nonstoichiometric molybdenum suboxide coupled with Pt nanoparticles (NPs) acts as a promising catalyst for this reaction, in which surface oxygen vacancies (VO) and the redox ability of Mo in molybdenum suboxide are the keys to transforming CO2 into the CO intermediate and further to afford CH3OH. In this study, a series of molybdenum oxides with different morphologies, including bulk, nanosheet, nanobelt, and rod morphologies, are used as catalysts, and the effects of particle morphologies on the catalytic performance toward CO2 hydrogenation are examined. A Pt-loaded molybdenum suboxide nanosheet (Pt/HxMoO3–y(Sheet)) with a high specific surface area affords 1.35 times greater CO2 conversion and CH3OH yield in liquid-phase CO2 hydrogenation compared with the corresponding bulk analog under relatively mild reaction conditions (total 4.0 MPa, 200 °C). Experiments and comprehensive analyses, including X-ray diffraction and in situ X-ray absorption fine structure studies, reveal that the enhanced activity of Pt/HxMoO3–y(Sheet) is attributable to a high concentration of surface-exposed VO sites, which are introduced in the (010) plane during the H2 reduction due to the high surface-to-volume ratio of the nanosheet-structured MoO3. In addition, the nanosheet-structured catalyst exhibits better reusability because of its antiaggregation behavior for Pt NPs compared with the conventional bulk analog.

Possibility Study in CO2 Free Hydrogen Production Using Dodecane (C12H26) from Plasma Reaction

Turquoise hydrogen refers to hydrogen produced through a fossil-fuel-based process in which carbon is separated into solid carbon and no carbon dioxide is produced. In this study, dodecane was selected as a simulated oil for waste plastic pyrolysis recovery oil, and the turquoise hydrogen production characteristics through the thermal cracking reaction using an arc plasma torch were investigated. The plasma was stably discharged at 2 to 4 kW. Hydrogen in the produced gas was analyzed through an online IR gas analyzer, and hydrocarbons from C1 to C5 were analyzed through GC-FID. As a result of the experiment, the hydrogen yield tended to increase as the plasma power increased, and a maximum of 11.5% based on mass was obtained. On the other hand, carbon oxides such as CO and CO2 were not generated. Along with hydrogen, the valuable by-products of this process are solid carbon and gaseous hydrocarbons. The solid carbon yields also increased up to 66% as the plasma power increased. On the other hand, the yield of gaseous hydrocarbons showed an opposite trend to that of hydrogen and carbon and consisted mainly of C2 series (average content of 77%) and olefins (average fraction of 0.67). Consequently, it can be considered that the plasma thermal cracking is a promising technology for the CO2-free hydrogen production, as well as solid carbon and C2-olefin.

CO2-free hydrogen production via microwave-driven methane pyrolysis

Hydrogen will play an integral role in achieving net-zero emissions by 2050. Many studies have been focusing on green hydrogen, but this method is highly electricity intensive. Alternatively, methane pyrolysis can produce hydrogen without direct CO2 emissions and with modest electricity inputs, serving as a bridge from fossil fuels to renewable energies. Microwaves are an efficient method of adding the required energy for this endothermic reaction. This study introduces a new method of CO2-free hydrogen production via non-plasma methane pyrolysis using microwaves and carbon products of this process. Carbon particles in the fluidized bed absorb microwave energy and create a hot medium (>1200 °C) in contact with flowing methane. As a result, methane decomposes into hydrogen and solid carbon achieving over 90% hydrogen selectivity with ∼500 cumulative hours of experiments This modular pyrolysis system can be built anywhere with access to natural gas and electricity, enabling distributed hydrogen production.

Co-Ni supported yttrium oxide material as a catalyst for ammonia decomposition to COx-free hydrogen

The preparation of CO2-free hydrogen by decomposing ammonia using non-precious metal catalysts has received widespread attention. Co-based catalysts have good catalytic activity and low synthesis costs. Therefore, we prepared a series of Y2O3-loaded Co and Co–Ni bimetallic catalysts by the co-precipitation method. The structure-activity relationship of the catalysts during NH3 decomposition was investigated by X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, and Temperature-programmed reduction by hydrogen. The ammonia decomposition performance of the bimetallic Co–Ni was examined to elucidate the effect of the relative amount of the active metal of the catalyst on the catalytic activity and compared it with the monometallic Co/Y2O3. Among the tested catalysts, 20Co–10Ni/Y2O3 showed the best catalytic performance as well as good stability. The ammonia decomposition rate of the 20Co–10Ni/Y2O3 catalyst was 85.02% at 550 °C and GHSV of 9000 mL h−1·gcat−1, which was 28.5% higher than that of the 20Co/Y2O3 catalyst. The high activity of 20Co–10Ni/Y2O3 catalyst was attributed to the uniform loading of Co and Ni, high specific surface area, and a large number of mesopores. At the same time, Co and Ni exhibited synergistic effects to produce suitable adsorption energy of nitrogen atoms, which further enhanced the catalytic activity of the catalyst.