Hydrogen technology and thermal analysis

Green energy – hydrogen circle – hydrogen economy

An essential cornerstone of the green energy and sustainable mobility paradigm is the utilization of hydrogen as a versatile resource for energy storage and a facilitator for energy transfer processes. This concept has given rise to what is commonly referred to as the “hydrogen cycle,” illustrating the journey of hydrogen from its generation, storage, and export to its use as a clean fuel, which can then be employed in the generation phase once more. A comprehensive understanding of hydrogen conductivity and its various applications is pivotal in advancing this vision.

Given the multifaceted nature of each phase within the hydrogen cycle, various research initiatives have been launched to bridge existing gaps and develop essential technologies that are not yet fully matured. The Fraunhofer Research Society, for instance, has played a significant role in this domain by formulating and disseminating a hydrogen roadmap for Germany. This roadmap provides a comprehensive overview of all the research areas and key topics, serving as a strategic guide to steer the country’s efforts towards a hydrogen-powered future.

The roadmap serves as a guide to envision the potential applications of hydrogen in the near future. Central to this vision are the fundamental challenges of hydrogen storage and production, given that these aspects significantly impact every sector. The overarching question revolves around how to securely and efficiently store hydrogen.

Hydrogen roadmap for Germany (source: Fraunhofer Institute)

the Hydrogen circle

Additionally, a critical aspect to address is whether a centralized or decentralized approach to hydrogen production is more viable. This consideration hinges on determining whether hydrogen should be utilized directly as a fuel or in alternative forms, such as ammonia or similar substances. The roadmap provides a strategic framework to explore and navigate these key decisions, shaping the future of hydrogen-based technologies and their integration into various sectors.

1. Hydrogen cycle – Renewable energy sources

The hydrogen cycle commences with the generation of hydrogen through green power plants. These power plants rely on a variety of renewable energy sources, including hydropower plants, wind turbines, photovoltaic arrays, geothermal facilities, and biomass plants. The ultimate objective is to harness energy in substantial quantities without generating CO2 emissions or nuclear waste.

The fields of thermal analysis and Material Science play a pivotal role in each of these renewable energy sources:

  1. Composite materials research focuses on their application in wind turbine blades.
  2. Material optimization is essential for enhancing the performance of semiconducting materials in photovoltaic cells.
  3. Optimization efforts are also directed toward the direct production of hydrogen from biomass applications.

These scientific disciplines are integral to the development and advancement of green energy technologies, contributing to the sustainability and environmental goals of the hydrogen cycle.

Application example: Thermal expansion behavior of light-construction-materials

An illustrative case where thermal analysis plays a crucial role in renewable energy is in understanding the thermal expansion behavior of lightweight construction materials, such as composites used for wind turbine blades.

Composite materials find extensive applications in lightweight constructions and specialized structural components. For instance, windmill blades are crafted from lightweight aluminum alloys or polymers.

Thermal analysis reveals subtle distinctions between two polymer composites designed for sturdy yet lightweight constructions, like wind turbine blades. Measurements were conducted using a Linseis pushrod dilatometer, with a constant heating rate of 5 K/min (depicted in the lower curve). The results indicate that there is no significant difference between the two materials in terms of the absolute delta L, which was measured during this analysis. Furthermore, the relative expansion (as shown in the red curves) closely aligns for both materials.

However, a nuanced variation comes to light when observing the Coefficient of Thermal Expansion (CTE). Prior to the transformation point at approximately 200°C, a subtle effect becomes discernible in one of the two samples, signifying an additional small transformation or phase change that the other material does not exhibit. This distinction underscores the precision and sensitivity of thermal analysis techniques in characterizing materials for renewable energy applications.

Application example: DEA – dielectric analysis / cure monitoring

Achieving cost-effective, high-quality production of composite materials hinges on precisely defining the time and temperature profiles required to ensure that each specific component reaches the desired state.

Selecting the wrong parameters can lead to a compromise in product quality or result in unnecessary expenditure. Monitoring and optimizing this curing process are vital, and this can be accomplished by employing Dielectric Analysis (DEA).

DEA sensors are utilized to observe the curing of most polymers by embedding them within the uncured material. In an illustrative scenario, a resin is isothermally heated to 180°C, with a DEA sensor in place to monitor the process. The red curve tracks the isothermal temperature of both the sample and the sensor, while the ion viscosity and the slope of ion viscosity are continuously assessed.

Three notable points, CP2, CP3, and CP4, denote critical stages in the curing process. CP2 marks the commencement, where the material exhibits minimum viscosity. CP3 signifies the peak reaction rate, with the maximum slope, and CP4 signifies the end of curing. This information is indispensable for ensuring the proper curing of polymers, as inadequately cured materials can result in significant quality issues.

Application example: quality and behavior of the raw materials e.g. biomass

In the production of hydrogen, the quality and characteristics of raw materials, such as biomass used for power and hydrogen generation, are of paramount importance. The key question revolves around determining the hydrogen yield from various raw materials during the gasification process, the energy requirements involved, and the overall output. These factors can be meticulously monitored using pressurized thermogravimetry and a combined thermogravimetry and calorimetry approach, as demonstrated in the following application example.

Biomass Gasification:

One common application for high-pressure TGA measurements involves investigating a process known as coal gasification or hydro-gasification. This method, which entails heating carbon in a steam-rich environment, finds application in catalytic processes, such as the removal of carbon monoxide from exhaust emissions, and the extraction of valuable organic compounds from resources like charcoal or biomass.

The provided example illustrates a typical gasification experiment involving dry biomass. The biomass sample is subjected to an isothermal plateau under a nitrogen atmosphere at 50-bar pressure (High-Pressure TGA – Thermo balance).

The mass signal reveals the loss of volatile components between 20 and 40 minutes. Following the introduction of water vapor, the biomass undergoes gasification, almost entirely consumed after 150 minutes. This transformation yields H2, CO, CH3OH, and other valuable reactive gases, as evidenced by the red mass loss curve.

The entire process can be summarized as follows: Carbon reacts with water vapor to produce a mixture of carbon monoxide and hydrogen. The generated carbon monoxide can then interact with a second water molecule to form carbon dioxide, along with additional hydrogen. Subsequently, the resulting hydrogen can be utilized to produce methane and other hydrocarbons from carbon monoxide. This intricate process holds significant implications for optimizing hydrogen production from renewable resources.

Application example: investigation of burning behavior and ash content of composites

Upon reaching the end of a product’s life cycle, the recycling or energetic utilization of composite materials becomes a critical consideration. In this context, investigating the burning behavior and ash content of these materials can be of significant interest.

Ash Content of Rubber:

Materials containing carbon, organics, and polymers typically burn off when subjected to heat. Investigating the thermal decomposition of such materials is unique in that it is often conducted in inert atmospheres, rather than in air, to facilitate the observation of decomposition effects and pyrolysis. Subsequently, a switch to oxygen or air is employed, leading to the combustion of the carbon content.

When this procedure is performed using a combined thermal analyzer (STA), it allows for the measurement of carbon content, inorganic content, and the released heat. In the case of an industrial rubber sample, the analysis was conducted using a simultaneous thermal analyzer (STA PT 1600) under a nitrogen atmosphere.

The sample underwent heating in three stages, each at a rate of 30 K/min. The blue curve in the graph illustrates the relative weight loss. The initial weight loss stage corresponds to the dehydration of the sample, with a water content of 9.3%. Notably, the corresponding DTA signal (depicted by the purple curve) did not exhibit any significant effects during the water evaporation process.

In the second reaction stage, volatile components were released via pyrolysis under a nitrogen atmosphere, contributing to a weight loss of 36.0%. This release was identifiable by an exothermic reaction peak on the DTA curve.

The third reaction stage involved a change in the atmosphere to oxygen (O2), leading to the combustion of the remaining carbon content. This resulted in a weight loss of 14.3%. The remaining 40.4% of the sample consisted of inorganic components such as ashes, slake, or fillers. This analysis provides valuable insights into the composition and behavior of rubber and other similar materials during thermal processes.

2. Transformation from electrical to chemical energy (Electrolysis, Synthetic Fuels)

Storing electrical energy has been a significant challenge, especially when considering the operation of large power plants. Traditional power plants, like coal and nuclear facilities, generate a continuous supply of energy to meet base load demand, while more flexible ones, such as gas plants, help compensate for fluctuations in demand.

Renewable energy sources, like solar and wind, face inherent fluctuations, such as those occurring at night, during dry spells, or when the wind subsides. To address the requirement for continuous and variable energy supply from intermittent renewable sources, energy storage becomes essential.

Furthermore, applications like long-range electric vehicles, trucks, and airplanes demand substantial energy quantities. Using conventional batteries for such large-scale energy storage is neither practical nor cost-effective. In such cases, it becomes more convenient to convert electrical energy into chemical energy in the form of synthetic fuels or hydrogen. Notably, synthetic fuels are produced using hydrogen, making the initial step the production of hydrogen through water electrolysis.

Water electrolysis is the process of splitting water into oxygen and hydrogen gas by applying an external voltage. Given that hydrogen generation through this process demands a significant amount of energy, alternative methods are also explored, including catalysts and reaction chains, such as coal gasification.

Nevertheless, the ultimate aim is to develop highly efficient and high-throughput direct electrolysis. To enhance the efficiency of electrolysis, optimization is required for cathode and anode materials, as well as catalysts and surface materials. This optimization is a key pursuit in achieving cost-effective and efficient hydrogen generation from water electrolysis.

Application example: Catalysts – Thermal expansion of platinum wires

Thermal analysis plays a critical role in this context by characterizing the materials used with respect to their chemical stability, thermal conductivity, sorption capability, and determining their thermal expansion characteristics. This comprehensive analysis not only enhances the longevity of materials but also ensures the quality of the components involved in energy storage and conversion processes.

Platinum, a widely employed catalyst, is used either in its pure form or as part of various alloys. Alloy usage is prevalent due to several advantages it offers, and it results in slight alterations in the physical and chemical behavior of the material. To illustrate this, we can examine the example showing the difference in thermal expansion between pure platinum and platinum alloyed with 3% rhodium.

In this instance, a Linseis pushrod dilatometer was used to measure both pure platinum and a platinum-rhodium alloy. The analysis involved linear heating at a rate of 5 K/min. The two lower curves in the data represent the absolute thermal expansion, while the upper curves depict the relative expansion of a platinum sample when compared to a platinum-rhodium alloy.

Despite the subtle difference in chemical composition, the expansion behavior exhibits a variation of several micrometers within the temperature range up to 1000°C. In the context of complex structures, such as reactors, precise knowledge of these expansion values is crucial. Failure to account for the differing expansion coefficients can lead to potential damage to components like electrolysis units, highlighting the importance of thermal analysis in optimizing and ensuring the reliability of energy storage and conversion systems.

Application example: Thermal Management – Thermal conductivity of graphite

In addition to addressing thermal expansion concerns within complex structures, the thermophysical properties, such as thermal conductivity and resistivity, hold paramount importance in managing heat effectively. The central objective is proficient heat management, aiming to maintain uniform temperatures within the reactor, thereby mitigating thermal expansion issues. Consequently, a comprehensive understanding of the thermal transport properties of all constituent materials is crucial.

To sum it up: Optimizing the thermal properties of hydrogen not only contributes to cost savings but also enhances overall quality. Nanostructured catalysts, for instance, offer a larger active surface area, resulting in reduced raw material consumption.

Graphite, a dark grey solid carbon species, exhibits significant chemical resistance and finds diverse applications, including its use as a cathode material, construction material, sensor component, and more. When exposed to heat, graphite reacts with oxygen to produce carbon monoxide or carbon dioxide. However, when heated in an inert, oxygen-free environment, graphite can reach extremely high temperatures, making it invaluable for ultra-high-temperature furnaces as furnace material or even as a heating element.

In a specific example, a graphite sample was subjected to analysis under vacuum conditions using a LFA 1000 (Laserflash Analyzer). The analysis involved the direct measurement of thermal diffusivity at multiple temperature steps ranging from room temperature to 1100°C. To determine the specific heat capacity, a known graphite standard was used as a reference in the same measurement setup.

The product of diffusivity, specific heat, and density yielded the corresponding thermal conductivity. The results exhibited a linear decrease in thermal conductivity, which is a characteristic trend. Additionally, the thermal diffusivity displayed a plateau above 500°C, and the specific heat capacity exhibited a slight increase with rising temperature. This detailed analysis provides essential insights into the thermal behavior of graphite, offering valuable information for a variety of applications and thermal management purposes.

Application example: Synthetic Fuel – Pressure dependent reactions by STA High Pressure

In certain applications, such as aircraft, it can be advantageous to store electrical energy in a more stable form than hydrogen, which leads to the utilization of synthetic fuels.

One significant advantage of synthetic fuels is their compatibility with existing infrastructures and designs. The concept involves using green hydrogen to create synthetic hydrocarbons, binding atmospheric CO2 during the formation process. However, during the usage (combustion) of synthetic fuel, the previously captured CO2 is released.

The production process of synthetic fuels, often referred to as the Fischer-Tropsch Process, can be optimized using high-pressure TG (Thermogravimetry) and TG/DSC (Thermogravimetry/Differential Scanning Calorimetry) systems, such as the LINSEIS High-Pressure STA (Simultaneous Thermal Analyzer).

The Linseis STA HP series facilitates controlled measurements under elevated pressure, which is crucial for several reactions. Many reactions exhibit pressure-dependent behaviors, especially for processes like decomposition, adsorption, and desorption. These behaviors are highly influenced by atmospheric conditions and pressure.

For instance, the provided curves demonstrate a comparative analysis of calcium oxalate hydrate decomposition under pressure (20 bar, represented by the red curve) and atmospheric conditions (blue curve). Notably, a substantial pressure dependence is observed for the decomposition steps 1 (loss of water) and 3 (loss of carbon dioxide). These steps shift to higher temperatures under elevated pressure.

The second step involves an irreversible transformation from organic oxalate to inorganic carbonate, releasing carbon monoxide. This step is pressure-independent as it is not reversible. Such insights into pressure-dependent reactions are vital for optimizing synthetic fuel production and enhancing their efficiency.

3. Hydrogen storage

The storage and transportation of hydrogen present notable challenges due to its highly volatile nature. While one method involves storing hydrogen gas by compressing it into cylinders, this approach is limited by the necessity for extremely high pressures (cylinders can reach a maximum pressure of up to 700 bar) and the associated technological and safety issues, as hydrogen has a propensity to diffuse through most materials over time.

To address these challenges, alternative technologies are preferred. Hydrogen storage can be achieved through sorption on various materials where it becomes chemically bound, examples of which include metal-organic frameworks (MOFs), zeolites, and ionic liquids. Nonetheless, the storage of hydrogen as a metal hydride holds the most promise.

In this approach, hydrogen is chemically bound to the surface of a metal, forming a stable hydride. This process can be optimized by increasing the surface area through the use of porous materials like zeolites and synthetic frameworks with nanopores. With this configuration, hydrogen can be released under controlled conditions of temperature or pressure changes, which can be easily managed. This method significantly mitigates the risk of uncontrolled diffusion, providing a safer and more effective means of hydrogen storage.

Application example: High pressure STA sorption

Thermal analysis, particularly gravimetric analysis, plays a crucial role in determining precise sorption conditions, release and storage rates, which are essential for optimizing loading and release cycles of hydrogen.

Typically, volumetric methods for sorption measurements provide information about the sorbed gas’s quantity but do not offer insights into the associated heat flow and enthalpy. To gain information about the heat of sorption, a separate experiment is usually required.

A more efficient alternative is the Gravimetric Sorption Analyzer (High Pressure TG-DSC), which simultaneously measures weight change (TGA – Thermogravimetry) and the DSC (Differential Scanning Calorimetry) signal. This combined analysis provides a quicker and more comprehensive understanding.

In a single experiment, the Gravimetric Sorption Analyzer can determine both the sorption capacity and the heat of sorption. The provided figure illustrates the DSC measurement aspect of the hydrogen adsorption on a Pt/Al catalyst at a pressure of 15 bar and a temperature of 80°C. The measured heat of sorption is 30.5 J/g and is directly determined during the sorption experiment, evident from the distinct peak in the curve. Additionally, the curve depicts the time from the introduction of hydrogen to the initiation of the sorption reaction, offering insights into the rate of interaction between the sample and the surrounding atmosphere. This comprehensive analysis significantly aids in the optimization of hydrogen storage and release processes.

4. Devices and processes using hydrogen as fuel

Once hydrogen is generated, stored, and made available for various applications, its high energy density opens the door to a multitude of uses. Some common applications include its use as a reducing agent, fuel, carrier gas, and in the synthesis of various molecules such as carbohydrates, ammonia, and more. One frequently encountered application is the sintering of metals.

In the production of metallic or metal-oxide-containing workpieces, powders are often compressed into “green bodies,” which are subsequently consolidated through a heating process below the melting point, known as sintering. During sintering, a reduction in dimensions is observed, making it possible to study the sintering process by measuring these changes. Dilatometers are typically employed for this purpose.

To prevent oxidation and reduce the oxide content in the final product, sintering can be performed in a hydrogen-containing atmosphere or even in a pure hydrogen atmosphere. LINSEIS, with its expertise in hydrogen safety technology, offers dilatometers designed for use in pure hydrogen atmospheres. These dilatometers can be utilized for hydrogen sintering or expansion measurements in reducing environments. The outgassing is coupled with a safety burn-off unit, and the system is equipped with a hydrogen detector capable of shutting down the system and flushing it with inert gas in the event of an uncontrolled hydrogen release.

Application example: H2 sintering of metal powders

The example demonstrates the hydrogen sintering of metal powder green bodies used as catalysts

The measurement illustrates the sintering curve of pressed sintered metal powder subjected to the sinter profile (lower curve) in an absolute hydrogen atmosphere. Hydrogen serves to reduce the oxygen content within the sample during the sintering process, leading to increased density and a reduced percentage of metal oxides. Consequently, both the gas atmosphere and sinter profile significantly influence the results.

The blue curve presents the relative expansion and shrinkage, while the red curve displays the absolute values. The primary sintering step is observed during the second heating phase between 500°C and 1400°C. This analysis is invaluable for optimizing sintering processes and achieving desired material properties.

5. Fuel cell technology

Fuel cells are among the most intriguing and widely discussed applications for hydrogen, with diverse applications ranging from providing electricity and heat to buildings to powering vehicles with extended range. Fuel cells play a pivotal role in the process of converting stored hydrogen back into electricity.

In a fuel cell, hydrogen undergoes a reaction with air to produce water. This reaction differs from direct combustion, which yields heat; instead, a fuel cell generates electrical energy. The schematic view of a hydrogen fuel cell illustrates its operation.

The objective is to generate electrical energy as needed by facilitating the reaction between hydrogen and oxygen. In contrast to a direct reaction that produces water with a significant release of energy in the form of heat (imagine igniting a hydrogen-oxygen gas mixture), a fuel cell comprises two chambers containing these compounds.

A membrane positioned between the chambers allows the diffusion of hydrogen while blocking the passage of other molecules. At the membrane’s surface in the chamber containing oxygen, the reaction between hydrogen and oxygen transpires, resulting in the production of water, which is expelled from the cell. This causes a reduction in hydrogen concentration at the membrane and encourages more hydrogen molecules to move toward the membrane. The diffusion of hydrogen to the oxygen-containing chamber generates an electrical voltage at the membrane. This electrical energy is harnessed for operating an engine, rather than being released as heat.

Fuel cell technology offers the advantage of being able to control the hydrogen concentration in the hydrogen chamber, allowing for easy regulation of the diffusion rate at the membrane, much like a gasoline-driven engine. Consequently, hydrogen can be considered the “fuel” in this context. The membrane is coated with electrode materials, typically composed of noble metals, which serve as catalysts and impact the fuel cell’s operating conditions, including temperature and voltage.

Hydrogen-driven fuel cells can function at high temperatures, even up to 1000°C, and the solder used for their assembly must be thermally, chemically, and mechanically stable. In this context, thermal analysis plays a significant role. The working conditions of fuel cells are closely tied to the materials used, particularly those serving as catalysts.

For the characterization of catalysts and materials, various analysis techniques are applied in hydrogen technology. In this context, thermal analysis techniques are particularly relevant.

Some hydrogen storage applications involve high-pressure conditions, occasionally exceeding 100 bar, making pressurized analyzers useful. Additionally, all analysis devices must incorporate safety features to mitigate the risk of hydrogen reacting with oxygen or air, which can lead to potentially hazardous explosions.

Operating temperature 40 – 90°C 40 – 200°C 60 – 130°C 200°C 650°C 40 – 90°C
Fuel H2 (/CO2) H2 Methanol H2 (/CO2) CH4, H2, CO CH4, H2, CO
Electrolyte Polymer KOH Polymer Phosphoric acid Molten carbonate Solid oxide

*Noble metals **Noble metals/Non-noble metals ***Non-noble metals

Application example: Hydrogen release from surface storage

Thermal analysis and material science equipment play a crucial role in the field of hydrogen energy and fuel cell technology, as demonstrated in the following application example:

Hydrogen storage can be achieved through various methods, including surface adsorption, pore adsorption, and chemical uptake. Among these, surface sorption is particularly promising for many metals, as it offers ease of implementation and precise control over hydrogen release. Therefore, extensive research is conducted on metals with high specific surface areas.

Titanium hydride is a commonly used hydrogen resource for controlled hydrogen release in various reactions. It serves as a catalyst in liquid chemistry, acting as an in-situ hydrogen source, and finds applications in batteries and fuel cells for controlled hydrogen release.

To understand the temperature-dependent decomposition behavior and the amount of heat released during this process, simultaneous thermal analysis (STA) is essential.

In this STA measurement, the release of hydrogen from titanium hydride was monitored. The measurement involved recording TG (Thermogravimetry) and DSC (Differential Scanning Calorimetry) signals as the sample was heated linearly in an Argon atmosphere at a rate of 10 K/min, spanning from room temperature to 800°C. Notably, between 300°C and 600°C, there is a two-step mass loss of 2.3% in total, indicating the complete release of bound hydrogen during this process. The corresponding desorption peaks are evident in the DSC curve (red curve), providing valuable insights into the hydrogen release characteristics of titanium hydride.

Safety equipment for Hydrogen measurements

Hydrogen is known for its high affinity to oxidants, metal surfaces, and oxygen. The reaction that forms water from its elements (2 • H2 + O2 = 2 • H2O; ΔH = 286 kJ/mol) is highly exothermic, making hydrogen a potent energy storage medium.

Hydrogen-air mixtures can be sensitive to explosions, particularly when the hydrogen content exceeds approximately 4%. While the activation energy for this reaction is high, in the presence of a flame, spark, or high temperature, such mixtures can burn or even explode. Therefore, when conducting thermal analysis that involves hydrogen concentrations greater than 4% in air, it is essential to implement safety precautions.

All LINSEIS thermal analyzers designed for hydrogen applications can be equipped with several key safety features to mitigate potential risks:

Hydrogen Detectors:

Hydrogen detectors are strategically placed in close proximity to the hydrogen instruments. They are designed to detect any hydrogen leakages or accidental releases promptly.

Safety Valves:

In the event of a detected hydrogen leakage, safety valves will immediately activate, cutting off the hydrogen supply to the thermal analyzer, thereby preventing any further hydrogen flow.

Flushing with Inert Gas:

Following the detection of a leakage and the subsequent shutdown of the hydrogen supply, the residual hydrogen within the analyzer is purged out using an inert gas to ensure that no flammable gases remain inside.

Burn-Off Unit for Outgassings:

All Linseis hydrogen systems are equipped with a burn-off unit at the outgas connector. This unit allows for the safe disposal of outgassings, including sample gas, purge gas, and decomposition products. These gases pass through a constant burning flame to ensure that no flammable gases are released into the environment, reducing the risk of critical gas concentrations in the laboratory. The flame unit is electrically heated and includes a safety mechanism to prevent any flame kickback into the gas lines. These safety measures help maintain a secure working environment when handling hydrogen in thermal analysis applications.

Linseis holds the global forefront in providing instrumentation tailored for hydrogen applications. Our extensive product range comprises:

  • Dilatometers
  • Simultaneous Thermal Analyzers
  • Thermogravimetric Analyzers
  • Thermomechanical Analyzers
  • Differential Thermal Analyzers

For further insights into our comprehensive offerings, please do not hesitate to contact us today.

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