The density of the hydrogen! The lightest of All!

The mass density of hydrogen gas at normal atmospheric pressure, temperature (NTP) is 0.0898 kg/m³. Comparing with the density of air which is approximately 1.225 kg/m³, hydrogen is approximately 15 times lighter than air at NTP. Find a detailed comparison: Hydrogen Compared with Other Fuels

At NTP, one litre hydrogen tank contains just 0.08376 g of Hydrogen where as one litre of gasoline/petrol has ~ 720 g of petrol.

Gasoline vapor density / Hydrogen density = 3.5 kg/m³ / 0.0898 kg/m³ ≈ 39. Therefore, hydrogen is approximately 39 times lighter than gasoline vapor.

A cubic meter of water weighs approx. 1,000 kilograms, where as a cubic meter of hydrogen gas weighs only 0.0898 kilograms. Therefore, hydrogen is approximately 11,940 times lighter than water at NTP.

Under normal temperature and pressure conditions (NTP), 1 kg of hydrogen occupies approximately 12,000 Litre, where as 1 kg of gasoline occupies just 1.34 Litre.

Hydrogen has 3× higher energy per mass than gasoline (33.3 kWh/kg vs. 12.7 kWh/kg). However, its gaseous state at NTP forces ~300× larger volume to store the same energy as gasoline.

Now you can easily imagine the density of the hydrogen!

Hydrogen Storage & Transportation challenges:

Due to its extremely low density, hydrogen in gaseous form takes up huge volume at normal atmospheric pressure. As a result, large, giant containers are required to store useful quantities of hydrogen in gaseous form in normal conditions. Thus hydrogen is virtually not stored or transported in gaseous form at atmospheric pressure because it is simply highly inefficient. Efficient and safe storage, transport of hydrogen is not a straightforward unlike fossil fuels gasoline, diesel, natural gas, coal, etc.,

Also hydrogen has very poor volumetric energy density, the amount of energy carried per unit volume.

Imagine a container holding one gallon of liquid hydrogen. That same amount of hydrogen, if it were a gas at standard temperature and pressure, would fill up a whopping 800 gallon containers approximately! This is because liquid hydrogen is incredibly dense compared to its gaseous form. When it changes state (from liquid to gas), it expands dramatically, undergoing a rapid phase change.

Volumetric Reduction is Crucial for Hydrogen Storage, Usage

• Practical Storage Size: Storing a usable amount of hydrogen energy at atmospheric pressure would require impractically large volumes due to its low density. Volume reduction is essential for practical applications.
• Vehicle Range and Packaging: For Fuel Cell Vehicles (FCEVs), volumetric energy density dictates fuel tank size and thus vehicle range. Higher density allows for smaller tanks integrated into vehicles.
• Transportation and Distribution Efficiency: Higher density enables more efficient hydrogen transport via pipelines, trucks, or ships, reducing infrastructure costs.
• Economic Viability: Reduced storage volumes can lower material requirements and infrastructure costs, improving the economic feasibility of hydrogen energy.

Hence for storage, transportation and for all practical purposes of hydrogen use, volumetric reduction is a must – it has to be compressed or super cooled to liquid state. This is the key limitation of using hydrogen as a fuel in mobility (Cars, ships, Trucks, etc.,). As hydrogen is produced at low production pressure (20-30 bar), hydrogen gas requires compression or state change to cryogenic liquid state before transportation.

Two Main Approaches to Hydrogen Storage:

A. Physical Storage:

Focuses on changing the physical state of hydrogen to increase its density for storage. Here there are two key traditional strategies: high-pressure compression and cryogenic liquefaction.

1. Compressed Gaseous Hydrogen: (CGH2) By compressing hydrogen gas to pressures ranging from 350 to 700 bar within specialized containment vessels, its density is significantly increased.

Volumetric Reduction Through Compression: 700 bar Gaseous Hydrogen

• Volumetric Reduction Factor (Approximate): Compressing gaseous hydrogen to 700 bar reduces its volume by a factor of approximately 400-500 times (ideally 700 times, but realistically considerably less due to real gas effects).
• Density Increase: This volume reduction is due to the increase in density from approximately 0.08376 kg/m ³ (gaseous STP) to 39.8 kg/m ³ (gaseous 700 bar) or 39.8 g/L
• Compressing beyond 700 bar, not much gain in volumetric reduction. At 1000 bar and above, approximately 49.5 kg/m ³ / 0.0495 kg/L

This is the most mature hydrogen storage technology, low cost. This energy intensive process needs approximately ranges 4.2 – 15% of the energy content (LHV) of the resulting compressed hydrogen.

• Technological Maturity: 700 bar CGH₂ storage is the most technologically mature and commercially established hydrogen storage method for vehicles today. It’s the technology used in current Fuel Cell Electric Vehicles (FCEVs) like the Toyota Mirai and Hyundai Nexo.
• Reasonable Volumetric Energy Density: While lower than LH₂, 700 bar CGH₂ achieves a volumetric energy density that is sufficient to provide a practical driving range for passenger cars (e.g., 300-400 miles or more). The ~400-500 times volume reduction is enough for vehicle integration.
• Ambient Temperature Operation: CGH₂ operates at ambient temperatures (or slightly above due to compression heat), avoiding the complexities and boil-off issues of cryogenic systems. This simplifies tank design and operation for everyday use.
• Faster Refueling Times (Potentially): Refueling with compressed gaseous hydrogen can be relatively fast, comparable to gasoline refueling (around 3-5 minutes), which is a key advantage for consumer acceptance in vehicles.
• Developing Infrastructure (700 bar Focus): The developing hydrogen refueling infrastructure for light-duty vehicles is largely focused on dispensing compressed gaseous hydrogen at 700 bar. This existing and growing infrastructure supports the practicality of 700 bar CGH₂ for vehicles.
• Lower System Complexity (Compared to Cryogenics): CGH₂ storage systems, while still complex pressure vessels, are generally less complex than cryogenic LH₂ or CcH₂ systems, which require vacuum insulation, boil-off management, and specialized cryogenic components. This translates to potentially lower system cost and easier maintenance for vehicles.

2. Liquid Hydrogen (LH2) or Cryogenic LH2: Hydrogen can be liquefied at cryogenic temperatures (around -253°C). This dramatic phase change results in a roughly 800 times increase in its density compared to the gaseous state. This means that 800 times more hydrogen can be stored in the same tank or container. The tank needs specialized thermal insulation. Storing liquefied hydrogen in cryogenic tanks is a very complex, energy intensive process.

Volumetric Reduction Through Cooling: Liquefying Hydrogen

• Process: Cooling hydrogen gas to liquid hydrogen (LH₂) involves lowering its temperature dramatically, from room temperature (approximately 20°C or 293K) down to its boiling point of -252.87 °C (20.28 K) at atmospheric pressure.
• Volumetric Reduction Factor (Approximate): Liquefying hydrogen reduces its volume by a factor of approximately 800 times compared to its gaseous volume at standard temperature and pressure (STP).
  • Analogy: Imagine 800 liters of gaseous hydrogen at room temperature condensing into just 1 liter of liquid hydrogen.
• Density Increase: This volume reduction is a direct consequence of the dramatic increase in density upon liquefaction, from approximately 0.08376 kg/m ³ (gaseous STP) to 70.8 kg/m ³ (liquid LH₂) or 70 g/L

However, this cryogenic liquid approach presents significant challenges:

• Hydrogen has a low ignition limit, high diffusion rate in air, and a low boiling point (-252.8 C). These properties necessitate specialized infrastructure for safe handling, significantly increasing the overall cost of using hydrogen as a fuel. While these methods offer a path to increased density, the safety considerations and infrastructure costs associated with them limit their widespread adoption.
• Storing liquid hydrogen costs 4–5 times more than using compressed gas technology.
• Environmental heat (heat from outside air, environment) or boil off phenomenon can cause up to 2-3% of hydrogen vaporizes per day from the liquid cryogenic tank through the safety valve. This release of hydrogen could potentially pose a significant safety risk.
• This cryogenic process is also highly energy-intensive. In practice, the energy input for liquefaction is typically around 20- 35% of the energy content (LHV) of the resulting liquid hydrogen.

Key Comparison Table

3. Cryo-Compressed Hydrogen storage (CcH2): Combination of the above two, this method combines elements of both compressed and cryogenic storage. This approach aims to achieve higher storage densities than compressed hydrogen alone, while reducing the complexity of maintaining extremely low temperatures needed for liquefaction.

CcH₂ involves cooling hydrogen gas to cryogenic temperatures, but warmer than liquid hydrogen (e.g., Range of -40 to -100 C), and simultaneously compressing it to moderate pressures (e.g., 150-350 bar, and sometimes higher in research). It operates in a temperature and pressure range between liquid hydrogen and compressed gaseous hydrogen.

Intermediate Volume Reduction: Cryo-Compressed Hydrogen (CcH₂) offers a range of volumetric reduction factors depending on the specific temperature and pressure conditions used in the CcH₂ process. Approximately 500 to 600 times, CcH₂ achieves a volumetric reduction that is intermediate between CGH2 and LH2

Key Features of Cryo-Compressed Hydrogen (CcH₂)/ Challenges Addressed by CcH₂:

• Energy Efficiency: Avoids the 30% energy loss of LH₂ liquefaction.
• Material Costs: Lower pressure (vs. 700 bar CGH₂) reduces tank costs for large-scale systems.
• Boil-Off Mitigation: Moderate cooling (−40°C to −80°C) minimizes evaporation compared to LH₂.
• Lower Liquefaction Energy than LH₂: CcH₂ avoids the full liquefaction process, requiring less extreme cooling and potentially lower overall energy consumption for storage compared to LH₂.
• Technology Under Development: CcH₂ is a promising advanced storage concept, but the technology is still under development and not as commercially mature as compressed gaseous or liquid hydrogen storage. Research is ongoing to optimize CcH₂ systems for practical applications.

Cryo-Compressed Hydrogen [ CcH2 ] – Key Comparison

CcH2: Key Advantages Over Other Storage Methods

B. Material Based Storage:

This approach utilizes special materials both solids and liquids that act like “carriers” for hydrogen. These materials can bond with hydrogen molecules or atoms, either physically or chemically. This method offers several advantages over physical storage:

• Higher Storage Density: By binding with hydrogen, these materials can pack it in more tightly, increasing storage capacity.
• Improved Safety: The bonding with the carrier material can make hydrogen less volatile and easier to handle safely.

Liquid Organic Hydrogen Carriers (LOHCs): This promising approach is at the forefront of innovation. LOHCs store hydrogen by chemically binding it to readily available liquid molecules at ambient conditions. The hydrogen can then be released through a controlled dehydrogenation process. LOHCs offer a trifecta of benefits:

• Safe and Simple: No high pressure or extreme temperatures are needed, reducing infrastructure costs and safety concerns.
• Tailored Options: Different LOHC molecules can be chosen based on desired properties. Some options even utilize atmospheric derivatives like CO2, potentially capturing greenhouse gases during hydrogen production.
• Easy Separation: Hydrogen separation from LOHCs is achieved through simple condensation due to the use of high-boiling-point liquid molecules.

Toluene / Methylcyclohexane is a well-studied LOHC system.

Metal-Organic Frameworks (MOFs): MOFs are porous crystal materials made of metal ions, where large pores within the crystals can store hydrogen gas1. MOFs have high surface areas and hydrogen adsorption capacities, where hydrogen molecules can cling to the surface of the MOF cavities. They have a simple charge/discharge mechanism, allowing the stored hydrogen to be released immediately upon discharge without the use of chemical reactions, which typically require high temperatures. MOFs have the potential to store hydrogen through adsorption at moderate pressures and temperatures.

Metal Hydrides: These materials store hydrogen through chemical bonding. This involves the formation of metal hydrides using elements like palladium, which has the capacity to soak up hydrogen up to 900 times its own volume, in addition to other elements such as magnesium, aluminum, and specific alloys. While some hydrides offer high storage capacities, challenges remain in terms of reversibility and energy efficiency of the hydrogen release process.

Nanomaterials: Nanomaterials are being explored for their potential in hydrogen storage.

Power Fuels: Power fuels are another form of material-based storage where hydrogen is stored in the form of power fuels.

Ongoing research is focused on developing new materials and techniques for even more efficient and safe hydrogen storage.

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Hydrogen Rainbow or Hydrogen colors, Yes, there exists a rainbow, a diverse spectrum of Hydrogen types! Colors or Codes or shades!

Hydrogen is always colorless, invisible at normal temperature or even liquefied or frozen metal!

Though most prevalent, abundant element in the universe, Hydrogen does not exist in nature (above the ground) by itself as it is highly reactive. Thus it must be manufactured produced or separated or extracted from other naturally occurring compounds, elements, reservoir hidden below Earth’s surface, biomass, all types of fossil fuels or water, etc.,

As global warming becomes severe day by day, the need for clean sustainable energy is inevitable. The world is seeing an extraordinary surge in efforts to realize hydrogen’s long-standing promise as a clean energy source. Hydrogen plays crucial role in the global transition to the clean energy or towards decarbonization of the industries towards net zero emissions.

Hydrogen colors, Hydrogen rainbow

There are many diverse ways of hydrogen production in the industry existing for decades. Hence there is a need to classify hydrogen by its production method, very importantly the energy consumption and greenhouse emissions mostly the carbon dioxide gas (CO2) and methane (CH4) during a production process. Depending on the production process, hydrogen is given a color, shade such as grey, brown, blue or green, etc like in the painting sector. This color coding scheme is called as the hydrogen rainbow or hydrogen spectrum or or color codes or simply hydrogen colors.

• irrespective of the color or production process, the same carbon-free molecule (H2) is produced in all the processes
• regardless of color, hydrogen from all methods, has exactly the same physical and chemical properties
• the color code is just for easy understanding and remembering easily the complex, diverse production methods
• the colors do not represent any scientific characteristics
• the colors used to identify the production processes have certain context specific meanings and some are really chosen randomly
• Hydrogen rainbow is a visual representation of the color spectrum, helping to explain the color scheme

However the energy requirements and greenhouse gas emissions for each of the production processes vary significantly. This aspect is very important and key to classify the production process for the net zero emission, sustainable clean energy industry.

Grey hydrogen is produced from natural gas (typically methane) by steam methane reforming (SMR) process. This is low cost, most common method of hydrogen production. Greenhouse gases (mostly CO2 here), made in the process are not captured. Thus no Carbon Capture, Utilisation and Storage (CCUS). Direct addition of greenhouse gases to atmosphere or water bodies.

Blue hydrogen is produced by the standard SMR process, same like gray hydrogen. However upto 95% of the CO2 is captured through Carbon Capture, Utilisation and Storage (CCUS) system. As the CO2 emissions from this process is not released into the atmosphere or water bodies, blue hydrogen is sometimes called as carbon neutral or low carbon hydrogen by some researchers.

Brown hydrogen is produced from brown color coal (lignite) using various gasification technologies which involves heating the coal. This is a low cost, most common method of hydrogen production. It produces toxic CO and CO2. No carbon capture or reduction of greenhouse gases (here CO2 mostly as CO reacts with water and produces CO2 and H2) emissions. If carbon capture is applied here for CO2 emission, the hydrogen produced becomes Blue Hydrogen

Black hydrogen is produced from black color coal (Bituminous) using the same gasification processes used for brown hydrogen production. No carbon capture. If carbon capture is applied for capturing the CO2 mostly, the hydrogen produced becomes Blue Hydrogen

White or geologic or natural hydrogen is extracted from the vast natural hidden hydrogen reservoirs under the surface of the earth or from the deep mines or ocean beds. This promises low cost and a game changer!

Turquoise hydrogen is produced from natural gas (has 70-90% Methane) through a process called methane pyrolysis. Use of high temperature decomposes methane directly into hydrogen and solid carbon. Solid carbon is known as synthetic graphite or carbon black used in numerous industrial applications. As it is solid carbon, no need to store in underground. This process has a very low carbon intensity.

Here electricity is used as the energy for direct heating and splitting methane, the entire process becomes carbon neutral if we use renewable electricity. Turquoise hydrogen looks very promising, could be a game changer for low carbon hydrogen production in comparison with green hydrogen production through electrolysis

Green hydrogen is produced by electrolysis of mostly pure water using renewable energy and very low emissions. It is high cost, as electrolyser cost is coming down, Green hydrogen is the key enabler for the global shift to sustainable clean energy and net-zero emissions economies

Yellow hydrogen is produced through electrolysis of water, from solar generated electricity. Hence technically a green hydrogen!

Gold hydrogen is a novel method of hydrogen production that involves injecting bacteria into depleted oil wells. These bacteria are capable of converting the residual hydrocarbons within these wells into CO2 and H2 gases. The hydrogen is then collected for use, while the CO2 is sequestered, making gold hydrogen a zero to negative carbon emission process. Gold hydrogen could cost much less, at a price of US$ 1/Kg or below. Hence Gold hydrogen is a game changer!

Pink or purple or red hydrogen is produced by electrolysis of water through nuclear power generated electricity or direct splitting the steam generated, using a catalyst and the heat produced from the nuclear reactor.

The hydrogen rainbow or hydrogen colors – The use of colors simplified the process of comprehension and keeping in mind easily of these potentially complex production systems, choosing the most beneficial options, and enhancing the understanding of a clean energy solution. This professional approach of hydrogen colors promotes comprehension and memory retention.

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There could be 5.5 trillion tons of natural hydrogen in underground reservoirs, throughout the Earth

Global Discoveries Spark Hydrogen Mining Boom: Natural, vast hydrogen reservoirs in the Albania, USA, France, Canada, Turkey, Finland, Oman and beyond are fueling a race among miners to tap into the vast, huge hidden hydrogen sources beneath the Earth’s surface. This has ignited a surge in startup activity, with a new generation of companies eager to exploit these untapped reserves of geologic or white or natural hydrogen. Few say color code for this natural hydrogen is gold. Echoing the oil boom of the early 20th century, the mining industry is once again on the cusp of a thrilling era of growth and innovation.

Since its discovery in 2012, the spontaneously recharging natural hydrogen reservoirs of Bourakebougou in Mali have been in production, marking a significant milestone in the field of sustainable energy. This breakthrough has not only transformed the energy landscape but also set a new standard for hydrogen exploration and production. However Hydrogen extraction and drilling is still in nascent stage, not matured like that of fossil fuels.

Major advantages or promises of Natural, Geologic hydrogen:

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