Hydrogen Storage in Solid State

The adverse effect of climate change has become more widespread in recent years. One of the main solutions to control this disaster is to shift focus toward clean sources of energy such as hydrogen. While hydrogen is sustainable, renewable, and less polluting, there are challenges in storing it to ensure efficient usage, especially for transport. Research on developing ways to store hydrogen in a solid form to increase its usage in automotives is underway.

Hydrogen fuel economy can help countries achieve their net zero emission targets. It can replace the use of fossil fuels, especially in automotives, which are responsible for a significant amount of carbon emission in the atmosphere. However, there are severe hurdles in the storage and usage of hydrogen. It is typically stored in a compressed gas or liquid form, which requires a lot of space and temperature-controlled climate. Scientists are now researching ways to convert hydrogen to a solid state to address the needs of the transport and stationary energy supply sector for low-pressure, low-volume hydrogen storage.

Research is being conducted to find technologies that can transform hydrogen into a sufficiently compact and efficient form for transportation. The current set of hydrogen-powered vehicles require large, heavy cylindrical tanks to hold compressed hydrogen gas. The energy penalty to compress gas into such tanks is high and they take up considerable room in the car.

Hence, scientists are working on technologies that can help solid materials physically absorb the gas or chemically combine with it. Storing hydrogen in a solid material makes it dense. Due to this change, compact gas tanks suitable for automotive interiors can be designed. However, such a system must work at a reasonable temperature, absorb hydrogen quickly, and promptly release into the fuel cell as needed.

New Innovations

1. Absorption by using a combination of two solids (metal hydrides) – Researchers funded by the EU devised a technique to hold hydrogen in a benign solid form. They worked on the “Fluorine substituted high-capacity hydrides for hydrogen storage at low working temperatures” (FLYHY) project to develop novel materials and processes for hydrogen storage in solid state.
2. Adsorption by using Metal Organic Frameworks (MOFs) – The US Department of Energy (DoE) created a research consortium called HyMARC, which has five DoE national laboratories and external labs to work on methods to store hydrogen in solid state. They discovered metal hydrides and related materials can chemically bond with hydrogen. However, hydrogen steams off as porous absorbents such as MOFs are unable to bind hydrogen strongly enough to hold it. Therefore, the team is working on making hydrogen’s MOFs easy to adhere to by adding low-coordinate metal cation sites and resolving related issues. 

They discovered a combination of lithium amide/magnesium hydride and mixed-metal borohydrides as a new storage solution. It requires a modular hydrogen tank with tubes placed next to each other and filled with the two solids. Through the process of absorption, hydrogen is dissociated into H-atoms and incorporated into the solid lattice framework. Therefore, hydrogen gas can be stored in a small volume under pressure of 70 bar. This is much lesser than a conventional tank where hydrogen must be kept under pressure of more than 700 bar.

 Hydrogen energy has the potential to become a mainstream fuel and completely replace fossil fuels in the future. It has the advantages of being environment-friendly, efficient, renewable, and cost-effective. However, hydrogen’s extremely low volumetric density makes storage difficult. Researchers are exploring effective storage techniques that would play a key role in establishing a sustainable hydrogen economy.