Hydrogen storage is the process of storing hydrogen as a fuel for various applications. Hydrogen is a clean and renewable energy source, but it has some challenges for storage. This article will explain what hydrogen storage is, how it works, and why it is important. We also look into some of the methods and technologies for storing hydrogen.
What is Hydrogen Storage?
Hydrogen storage is preserving hydrogen in a specific state and condition to use it later as an energy carrier. It can be stored in various ways, depending on the physical state, pressure, temperature, and the material that holds the hydrogen. The storage methods include mechanical approaches such as using high pressures and low temperatures or employing chemical compounds that release H2 upon demand.
How Does Hydrogen Storage Work?
Hydrogen storage works by changing the properties of hydrogen to make it more compact and stable. We can store hydrogen in three forms: gas, liquid, or solid.
Each of these forms has advantages and disadvantages for storage.
Gas
Hydrogen can be stored as a compressed gas in high-pressure tanks. This is the most common and simple way of storing hydrogen, but it requires a lot of space and energy to compress the gas. Compressed hydrogen tanks can store about 5% of hydrogen by weight and 0.03 kg of hydrogen per liter of volume.
Liquid
Hydrogen can be stored as a liquid in cryogenic tanks. This is a more efficient way of storing hydrogen but requires very low temperatures to keep the liquid from boiling. Liquid hydrogen tanks can store about 8% of hydrogen by weight and 0.07 kg of hydrogen per liter of volume.
Solid
Hydrogen can be stored as a solid in various materials that can adsorb or absorb hydrogen. Adsorption is when hydrogen molecules stick to the surface of a material, while absorption is when hydrogen molecules enter the structure of a material. Solid hydrogen storage materials can be metals, alloys, compounds, or nanomaterials. Solid hydrogen storage can achieve higher densities and lower pressures than gas or liquid storage, but it may require high temperatures or catalysts to release the hydrogen.
Why is Hydrogen Storage Important?
Hydrogen storage is important because it enables using hydrogen as a clean and renewable energy source. Renewable energy sources, such as solar, wind, or hydropower, can produce hydrogen from water. Various devices, such as fuel cells, turbines, or engines, can use hydrogen to generate electricity, heat, or motion. Hydrogen can also balance the supply and demand of electricity grids and store excess energy from renewable sources. Hydrogen storage can help reduce greenhouse gas emissions, improve energy security, and diversify energy sources.
What are Some of the Methods and Technologies for Hydrogen Storage?
There are many methods and technologies for hydrogen storage, each with different characteristics and challenges. Some of the current and emerging methods and technologies are:
High-pressure tanks
These are cylindrical or spherical tanks made of steel or composite materials that can withstand high pressures of up to 700 bar. High-pressure tanks are widely used for storing hydrogen in vehicles, such as cars, buses, or trucks. High-pressure tanks are relatively cheap and easy to manufacture, but they are heavy and bulky, and they have safety and durability issues.
Cryogenic tanks
Insulated tanks can store hydrogen as a liquid at very low temperatures of around -253 °C. Cryogenic tanks use these insulated tanks for storing hydrogen in space applications, such as rockets or satellites. Cryogenic tanks can store more hydrogen than high-pressure tanks, but they are more expensive and complex, and they have high energy losses due to boil-off.
Metal hydrides
These are materials that can absorb hydrogen and form compounds called hydrides. Metal hydrides can store a lot of hydrogen in a small volume, but they have low gravimetric density, meaning they are heavy for the amount of hydrogen they store. Metal hydrides also need high temperatures to release the hydrogen, and they have slow kinetics, meaning they take time to absorb and release the hydrogen.
Chemical hydrides
These are materials that can react with water and release hydrogen. Chemical hydrides can store more hydrogen than metal hydrides, but they have similar drawbacks of low gravimetric density, high release temperature, and slow kinetics. Chemical hydrides also need a source of water and a way to recycle the by-products of the reaction.
Nanomaterials
These are materials that have very small structures, such as nanotubes, nanowires, or nanoparticles. Nanomaterials can store hydrogen by adsorption or absorption, and they can have high surface area, high porosity, and tunable properties. Nanomaterials can potentially store more hydrogen than conventional materials, but they are still under development and face challenges of scalability, cost, and stability.
Conclusion
Hydrogen storage is a key technology for using hydrogen as a clean and renewable energy source. Gas, liquid, or solid storage are different ways to store hydrogen. Each of these methods has advantages and disadvantages for storage performance, cost, safety, and environmental impact. Hydrogen storage can help reduce greenhouse gas emissions, improve energy security, and diversify energy sources. Researchers and developers are still exploring and improving new methods and technologies in the challenging and active area of hydrogen storage.
