Organic supramolecular crystals with high hydrogen storage performance could enhance fuel-cell vehicle efficiency

Hydrogen is commonly seen because the gas of the longer term on account of its zero-emission and excessive gravimetric power density, which means it shops extra power per unit of mass in comparison with gasoline. Its low volumetric density, nonetheless, means it takes up a considerable amount of house, posing challenges for environment friendly storage and transport.

To be able to deal with these deficiencies, hydrogen have to be compressed in tanks to 700-bar stress, which is extraordinarily excessive. This example not solely incurs high costs but in addition raises security considerations.

For hydrogen-powered fuel-cell autos (FCVs) to change into widespread, the US Division of Vitality (DOE) has set particular targets for hydrogen storage systems: 6.5% of the storage materials’s weight needs to be hydrogen (gravimetric storage capability of 6.5 wt%), and one liter of storage materials ought to maintain 50 grams of hydrogen (a volumetric storage capability of fifty g L^‒1). These targets be sure that autos can journey cheap distances with out extreme gas.

One promising technique to attain these targets is to develop porous adsorbent supplies, corresponding to metal-organic frameworks (MOFs), covalent natural frameworks (COFs), and porous natural polymers (POPs). All these supplies share a standard characteristic: they possess a porous construction that enables them to successfully entice and retailer hydrogen gasoline. This method additionally goals to facilitate hydrogen storage at decrease stress, corresponding to inside 100 bar.

Regardless of developments in surpassing the DOE’s gravimetric goal, many adsorbent supplies nonetheless battle to fulfill volumetric capability wants, and few can steadiness each volumetric and gravimetric targets. From an industrial standpoint, volumetric capability is extra essential than gravimetric capability, as car storage tanks have restricted house.

A hydrogen storage system’s quantity immediately impacts the driving vary of FCVs. Subsequently, growing hydrogen adsorbents that maximize volumetric capability whereas sustaining wonderful gravimetric capability is important. Attaining this purpose includes balancing a excessive volumetric and gravimetric floor space inside the similar materials.

Researchers are investigating varied supplies for hydrogen storage, with natural supramolecular crystals meeting from natural molecules by means of noncovalent interactions, being a promising choice because of their recyclability. Their potential stays largely untapped, nonetheless, as a result of designing supramolecular crystals with balanced excessive gravimetric and volumetric floor areas, whereas sustaining stability, is troublesome.

A phenomenon often known as catenation, which includes mechanically interlocked networks in porous supplies, sometimes enhances stability. Catenation, nonetheless, typically reduces surface area by blocking accessible surfaces, making the fabric much less porous and usually undesirable for hydrogen storage. Efforts are often made to reduce or keep away from it.

To unlock the potential of supramolecular crystals for hydrogen storage, a collaborative analysis workforce led by Professor Fraser STODDART, together with Analysis Assistant Professors, Dr. Chun Tang, Dr. Ruihua Zhang from the Division of Chemistry, The College of Hong Kong (HKU), and Professor Randall Snurr from the Division of Chemical and Organic Engineering, Northwestern College, US, demonstrated a managed “point-contact catenation strategy.”

The analysis is published within the journal Nature Chemistry.

This progressive method makes use of hydrogen bondsthe cross-section of which will be seen as a “point,” somewhat than the standard (π···π) stacking which includes giant “surface” overlap, to information catenation in a exact method in supramolecular crystals. Based mostly on this technique, researchers create a well-organized framework that minimizes floor loss attributable to interpenetration and tailors the pore diameter (~1.2–1.9 nm) for optimum hydrogen storage.

In consequence, the analysis workforce obtained a supramolecular crystal with record-high gravimetric (3,526 m² g^‒1) and balanced volumetric (1,855 m² cm^‒3) floor areas amongst all of the reported (supra)molecular crystals, along with excessive stability, whereas (i) bringing about wonderful material-level volumetric capability (53.7 g L^‒1), (ii) balancing excessive gravimetric capability (9.3 wt%) for hydrogen storage beneath sensible stress and temperature swing situations (77 Okay/100 bar → 160 Okay/5 bar), and (iii) surpassing the DOE final system-level targets (50 g L^‒1 and 6.5 wt%) each volumetrically and gravimetrically, albeit at cryogenic temperatures.

Revolutionary design

Designing natural supramolecular crystals that steadiness excessive gravimetric and volumetric floor areas, whereas additionally sustaining excessive stability, is a momentous problem, which has hindered its potential for a lot of purposes.

The workforce, nonetheless, has proposed a point-contact catenation technique that makes use of point-contact interactions involving hydrogen bonding to reduce floor loss throughout catenation. This design technique endows these supramolecular crystals with balanced excessive volumetric and gravimetric floor areas, excessive stability, and splendid pore sizes for hydrogen storage.

This analysis unlocks the potential of natural supramolecular crystals as promising candidates for onboard hydrogen storage and highlights the potential of a directional catenation technique in designing strong porous supplies for purposes.