When nano- meets climate technology

The use of metal-organic frameworks (MOFs) to create nanoscale crystal structures to attract hydrogen molecules could drastically improve the energy efficiency of storing and transporting the energy carrier.

The warmest years since global temperature records were first established, in 1880, have all unfolded since 2010, with the period from 2014 to 2022 standing out as the nine warmest years. Needless to say, climate change is upon us and it is a clarion call for an energy transition.

Samer Taha

A combination of energy efficiency, electrification, and renewables can potentially achieve 70% of the emissions mitigation needed to limit the rise in average global temperature by 2050 to 1.5 C above pre-industrial levels.

Hydrogen is expected to contribute 10% of that mitigation. In fact, efficient, cost-effective, and safe storage and transportation of hydrogen could enable its use in place of fossil fuels. There is a catch, however. The exceptionally low density of hydrogen renders existing storage methods costly, challenging, and inefficient. The convergence of nanotechnology and climate technology, however, presents a transformational opportunity to enable the big transition of the global energy system.

Trade-offs

Analyst McKinsey expects clean hydrogen demand will climb to 585 million tons per year by 2050, under a global net-zero carbon scenario. Effective storage and transportation of the energy carrier poses significant challenges, however. Due to hydrogen’s low density, high-pressure compression of up to 700 bar is necessary for storage, resulting in high energy consumption and costly equipment.

While liquefaction may offer advantages in terms of the transportation of hydrogen, there is the trade-off of high energy consumption during the process – it is even more energy intensive than storing hydrogen under high pressure.

The extremely challenging nature of handling hydrogen raises questions about realizing its potential while prioritizing environmental concerns. The key, therefore, is to seek better alternatives where traditional methods fall short.

Transformative forces

A novel approach at the atomic level may just hold the key to propelling the hydrogen economy forward.

Findings in reticular chemistry – a scientific discipline originally established by Omar Yaghi which involves linking molecular building units into extended two-and three-dimensional ordered structures using strong bonds – offer promising solutions to tackle the challenges that hinder efficient hydrogen storage and transportation.

What if it is possible to store and transport hydrogen in solid state, “adsorbing” it – transferring molecules from a fluid to a solid surface – into specially engineered nanomaterials?

There are several unique properties that make nanomaterials, especially MOFs, suitable for hydrogen storage. MOFs are materials designed with atomic precision which are characterized by tunable properties which can be adjusted by varying the metal ions and organic linkers used in their synthesis. This versatility makes it possible to design MOFs to accommodate tailored functionality in terms of specific pore sizes, shapes, and surface characteristics. There lies the potential to overcome many limitations of traditional hydrogen storage methods. In fact, the use of MOFs in hydrogen storage has been recognized by several government institutions and initiatives.

Simply put, hydrogen storage using MOFs can be thought of as a combination of organic molecules with metal atoms to form a nanoscale crystal structure. Highly porous MOFs can adsorb and retain hydrogen molecules, similar to how a sponge absorbs water. MOFs, with their lattice framework made of metal ions, or clusters coordinated with organic ligands, contain microscopic unfilled areas within their structure. These “voids” or “pores” enable hydrogen gas molecules to enter and stick to the MOFs’ surfaces. The hydrogen gas is then adsorbed onto the void surfaces.

This unique, hollow, cage-like structure enables MOFs to exhibit exceptionally high surface areas which can be optimized with atomic precision so they attract hydrogen molecules. Other classes of reticular materials, such as covalent organic frameworks and hydrogen-bonded organic frameworks, hold similar potential to attain high hydrogen storage density at low pressure.

Energy savings

An ideal hydrogen storage solution needs to allow for storing hydrogen molecules at a high density without consuming a lot of energy in the charging phase while also enabling the release of stored hydrogen with minimal energy consumption. The charging rate needs to be high enough to allow for a fast fueling time and the discharging rate needs to be high enough to match the requirements of fuel cells or other downstream processes. Reticular chemistry offers precise control of the composition and properties of nanoscale cavities in novel materials and this facilitates the design of materials that can attract hydrogen molecules into cavities without excessive bonding, enabling their release with minimal energy, when required.

This approach diverges from traditional high-pressure storage methods by pulling in and holding hydrogen at low pressure, using reticular materials. The materials attract hydrogen molecules into nanoscale cavities and retain them with bonding, allowing for efficient release of stored hydrogen, even in large amounts, on demand.

With MOFs it is possible to achieve high storage density at ambient temperatures and pressures as low as 20 bar. The novel technology thus enables high hydrogen storage density without the need for liquefaction or high-pressure tanks. This energy-efficient solution also reduces operating costs versus high-pressure hydrogen tanks which, simulations have shown, can cause additional annual energy expense of up to $12,000 for operating a fuel-cell transit bus.

Net-zero

Facilitating the hydrogen economy is indispensable to combating climate change. Leveraging decades of discoveries and advancements in reticular chemistry has enabled the development of novel materials with atomic precision to tackle the complex properties of hydrogen molecules. Mitigating the challenges that accompany the practicalities of hydrogen storage and transport makes phasing out fossil fuels more achievable. That is to say, carbon emissions can be significantly cut down, making the goal of net-zero emissions less of a distant dream.

About the author: Samer Taha, CEO and co-founder of H2MOF and executive chairman of Revonence, a private equity holding group, has more than 20 years’ experience in R&D, technology commercialization, and entrepreneurship in information and communication technology (ICT) and nanotechnology. He has founded and lead the expansion of two ICT startups, delivering of more than $200 million worth of ICT projects.

This post appeared first on PV Magazine.

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