Using Nanomaterials to Store Hydrogen for a Cleaner Alternative to Fuel Cars

6 min readOct 15, 2022

The automobile industry is synonymous with the American Dream and responsibility. In high school, we wait for the moment we can finally grab the flimsy white card that is our license and use it to drive a car. In a few years, I’ll be able to enjoy this pleasure but the effects of the automobile industry have got me questioning whether I truly want to drive a car.

The automobile industry is responsible for about one-third of all U.S. air pollution. Releasing smog, carbon monoxide, and other toxins, the fossil fuels utilized in cars are harmful to our health and our environment. A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide annually. One tonne of CO2 is equivalent to a 500 m3 hot air balloon. The improvements in CO2 emissions are not happening quickly enough according to Figure 1.

To reduce emissions more drastically, we need to look into alternatives to gasoline. Researchers at Northwestern have proposed the use of metal-organic frameworks to store hydrogen: a green fuel when burned, it produces a byproduct of water.

How do Traditional Combustion Engines Works

Why do we need gasoline in the first place, moreover what does it do? Once you step on the accelerator pedal, this releases the gas from the tank to the carburetor. The carburetor mixes the gas with air– a mixture that will be later utilized in later processes. In an engine, there are fixed cylinders that house pistons. There is a 4 stroke system to produce a motion within the pistons.

Intake — A valve within the cylinder opens to let in a mixture of fuel and air. This fills up the cylinder, pushing the piston down.
Compression — Once the piston reaches the bottom of the cylinder, the valve closes. The piston starts to move up to compress the gas.
Power stroke — A spark ignites the fuel and air mixture which creates pressure. This pressure pushes the piston down.
Exhaust — The valve opens up again and the piston travels up. This allows the excess exhaust gases to leave the piston, clearing it for another round.

While these 4 strokes are occurring, the pistons are connected to a crankshaft. This crankshaft rotates as the pistons translate up and down. This rotary motion is translated through gears which ultimately rotates the wheels.

Hydrogen Powered Cars — How they work? What are the barriers?

Now jumping forward to Hydrogen Powered cars, they are a quieter, energy efficient, and zero emissions alternative while still having the same performance and range as a gas-powered car. Hydrogen Powered cars would completely eliminate the need for an internal combustion engine and replace it with a battery. It would work similarly to EVs we see today, except, instead of needing to be charged, the car would produce the electricity while on the go.

These hydrogen-powered cars are made up of several fuel cells (aka a Hydrogen Fuel Cell Stack) to generate electricity. Hydrogen fuel cells produce electricity by using a REDOX (reduction/oxidation) reaction, a multi-step process, between hydrogen and oxygen to turn energy into electricity. This process is similar to a battery.

One fuel cell is comprised of two electrodes (anode and cathode), an electrolyte (catalyst), fuel (hydrogen), and a power supply. The anode (positively charged) and cathode (negatively charged) are separated with the electrolyte in the middle, which only allows for the transfer of protons. Here are the steps of how the reactions occur:

At the anode (+), there are hydrogen molecules which are then split apart of their protons and electrons.
The protons then migrate through the electrolyte to the cathode. Flow plates assist in this transfer. Electrons are then forced to move through a circuit, with this flow of electrons generating electricity.
The protons and electrons move to the cathode. At the cathode, there are oxygen molecules. When the subatomic particles come into contact with oxygen, this produces water molecules, and H2O. Heat is also produced as a byproduct.
The electricity created is then converted to a usable form of energy for the car through the power converter. The H2O molecules that are produced as a byproduct of the reaction are discarded through the tailpipe.

While the idea of Hydrogen-powered cars seems innovative and one of the many solutions to our climate change problems, they cost more than comparable-sized conventional cars.

Nanotech’s Role in Housing The Hydrogen

As cost is one of the biggest barriers to the adoption of hydrogen-powered cars, the storage of hydrogen is a big driving factor. Hydrogen gases are required to be kept in high-pressure compression. This pressure is 300 times the amount of pressure used to store gas in traditional cars. This high pressure is needed because hydrogen is a very low-pressure gas. Not only this is costly but unsafe. A team at Northwestern University works on solving this problem by using Material Organic Frameworks (I’ll explain this more later).

In order to find an efficient way of storing hydrogen, the proposed system needs to account for certain metrics in gravimetric storage capacity (the weight of a storage tank required to store some amount of hydrogen) and volumetric storage capacity (the amount of H2 adsorbed per unit volume). The volumetric storage capacity is applicable to is absorbents, porous solids that are capable of absorbing gasses or liquids.

Metal-Organic Frameworks (MOFs) fall under the category of nanotechnology. According to Nanowerk, MOFs are metal molecules and organic molecules that are connected in a framework. This framework consists of an array of positively charged metal ions surrounded by organic ‘linker’ molecules. MOFs contain crystal sponges that contain pores (Definition from Nanowerk). This makes MOFs an ideal choice to store hydrogen as it is highly porous. The porosity helps in keeping the pressure down in the fuel tank, so there isn’t a gradient in the flow of hydrogen. The gradient referred to means that the pressure of hydrogen flow to the engine tends to decrease as there is less fuel in the engine.

The current tradeoff with materials proposed to store hydrogen is that they aren’t able to fit both criteria of volumetric and gravimetric capacities. The research team at Northwestern found a MOF that fulfills both criteria (the criteria values are set in place by the US Department of Energy). NU-1501-A is a type of MOF. The thing that makes this MOF more special than the rest of MOFs is the distribution of pore sizes which affects how the NU-1501-A can store the gas.

Conclusion

Hydrogen-powered cars are a promising green alternative to gas cars with fact being that it produces zero emissions. To work towards this future, advancements in technology are needed. While MOFs can lower the cost of storing hydrogen, there is a need to be able to mass produce these MOFs. There is also a need for infrastructure so that these cars can get the needed hydrogen on the road. Similar to how we have gas stations, we will need hydrogen stations in the future. Overall, while MOFs do still need to be further developed, they unlock a new path for hydrogen-powered cars that will continue to grow as research continues and a need for a green alternative for cars arises.