Green Hydrogen Storage–Developments Across Different Types

Introduction

Several applications like ammonia and methanol production, oil refining, and steel manufacturing require and use hydrogen abundantly. Green hydrogen and fuel cell technologies have gone through cycles of high expectations but followed by impractical realities. This time around, however, several other factors are also in play – stringent climate change requirements, falling renewable prices, and rapid technological developments. These are leading to the use of green hydrogen as a realistic option for its role in climate change and green transition. Some challenges related to hydrogen storage need to be still addressed.

Types of Hydrogen storage

Hydrogen can be stored in the form of gas or also in the form of liquid. Hydrogen can be stored in the form of gas using high-pressure tanks, whereas liquid hydrogen can be stored by cooling it to cryogenic temperatures because the boiling point of hydrogen at one-atmosphere pressure is −252.8°C. A lot of research is happening to store hydrogen on the surfaces of solids using adsorption or within solids using absorption.

High-pressure compression of hydrogen

This is one of the most common methods of hydrogen storage. Storage of hydrogen as a gas typically requires high-pressure tanks (350–800 bar tank pressure). In this method, high-pressure gas steel cylinders are operated at a pressure of around 350 Bar. To achieve higher pressure up to 800 bar, composite material cylinders are developed that can achieve a volumetric density of around 36 kg/m³.

Liquid Hydrogen

Hydrogen can also be stored by converting it into the form of liquid by decreasing the temperature of the hydrogen at a constant pressure to obtain the liquid phase. Liquid hydrogen is stored in cryogenic tanks at -252°C at ambient pressure.

A pilot program was started in December 2019, as a partnership between Kawasaki Heavy Industries, Shell Japan, Iwatani Corporation, and J-Power. As part of the program, Kawasaki delivered a ship designed to carry 1,250m3 liquid hydrogen by compressing it at 1/800th of its regular gaseous volume and cooled to -253°C. This liquid hydrogen will be transported between the south coast of Australia and Kobe, Japan.

LOHC

This technology is based on an organic oil-like substance that binds hydrogen chemically. LOHC compounds are charged to store the hydrogen and discharged when there is a need for using hydrogen in certain applications.

Various compounds, including dicyclohexylmethane (DCHM), diphenylmethane (DPM), Methylcyclohexane (MCH), etc. are some of the compounds used storing and transporting technology.

Hydrogenious, H2Industries, and Chiyoda are some of the solution providers that have commercial LOHC solutions in the market.

In Dec 2019, Hydrogenious received investment from of 3.5 million euros. The consortium will use Chiyoda’s LOHC technology for study towards Green Hydrogen applications.

Metal Hydrides

Metal hydrides are the technologically relevant class of hydrogen storage materials. These can be used in a range of applications for hydrogen storage. Metal hydrides such as Magnesium hydride, Sodium aluminum hydride, Lithium aluminum hydride, ammonia borane, etc. are used as metal hydrides for hydrogen storage.

In Jan 2020, material researchers from Helmholtz-Zentrum Geesthacht (HZG) University in Germany, published a new concept using metal hydrides. In it, the hydrogen storage systems could be refilled five times faster and would require a three times smaller volume of a tank as compared to that of earlier concept. Researchers developed a concept of addition of potassium and lithium titanate oxide, which are ground together with the magnesium-nitrogen system for improving the surface area of the individual particles allowing them to bind more hydrogen.

Metal-Organic Frameworks (MOFs)

MOFs are a class of crystalline materials that are being researched for purpose of hydrogen storage due to their high specific surface area and tailored pore dimensions and are considered as ideal materials for hydrogen storage based on physisorption. It consists of metal ions linked together by organic ligands. It results in a highly microporous network.

In Dec 2018, researchers from the University of California, Berkeley, and Lawrence Berkeley National Laboratory set a new record for hydrogen storage capacity by using MOFs under normal operating conditions.

Hydrogen Storage in Ammonia

Research is going on to use ammonia as a medium to store and transport hydrogen it has several desirable properties that suggest its use as a medium to store hydrogen. Ammonia can be stored at room temperature at 9.2 in the inexpensive pressure vessel. Hydrogen also constitutes Hydrogen 17.65% of the mass of ammonia, which one of the positive points for the use of ammonia as a hydrogen storage material. There are several challenges like safety, efficiency, etc. these challenges need to be addressed for further developments.

Challenges related to Hydrogen storage

One of the key challenges with hydrogen storage is its low ambient temperature density that results in a low energy per unit volume. The requirement of high-density hydrogen storage is also a significant challenge for stationary and portable applications. It’s a significant problem for the transportation applications industry. A large-volume system for storage of hydrogen may not be a key issue for stationary applications but creates a problem for the applications in the automotive industry.

Future Outlook

Hydrogen and electricity generated from renewable resources, as energy carriers, are complementary in the energy transition. Hydrogen from renewables has the potential to channel renewable power to sectors where decarbonization is a need of an hour to maintain global warming under specified limits in the future. Hydrogen storage is also a key technology for the advancement of fuel cell technologies in applications in transportation. Even though hydrogen has the highest energy per mass for any fuel; its low ambient temperature density results in a low energy per unit volume, therefore requiring the development of advanced storage methods that have the potential for higher energy density will play a vital role in the future role of hydrogen in the green energy transition