By Syona Gupta • Youth Committee Member
Automobiles are synonymous with the American Dream and adulthood. In high school, we wait for the moment we can finally grab the 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 automobiles have got me questioning whether I truly want to drive a car.
The automobile industry is responsible for nearly one-third of all US air pollution. Releasing carbon dioxide (CO2), 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 ton of CO2 is equivalent to three large pigs or seven oil barrels. The improvements in CO2 emissions are not happening quickly enough.
To achieve a meaningful reduction in emissions, we need to investigate alternatives to gasoline. Researchers have proposed the use of metal-organic frameworks to store hydrogen. Hydrogen, a green fuel if produced by clean energy, produces a byproduct of water when burned.
How Do Traditional Combustion Engines Work?
How does gasoline power an engine? Once you step on the accelerator pedal, gas is released from the tank to the carburetor. The carburetor combines the gas with air, and this mixture then enters the engine. In an engine, there are fixed cylinders that house pistons. Conventional engines use a four-stroke system to produce power.
Intake — A valve within the cylinder opens to let in the mixture of fuel and air. This fills up the cylinder, while the piston is pulled 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 again and the piston travels up. This allows the excess exhaust gases to leave the cylinder, clearing it for another round.
While these four strokes are occurring, the pistons are connected to a crankshaft. This crankshaft rotates under the force of the power strokes. This rotary motion moves the drive shaft which ultimately rotates the wheels.
Hydrogen Powered Cars: How Do They Work? What Are the Barriers?
Now jumping forward, hydrogen-powered cars are a quieter, energy efficient, and zero emissions alternative to gas-powered cars while still having the same performance and range. Hydrogen cars eliminate the need for an internal combustion engine by replacing it with a system for producing electricity from hydrogen. These “fuel cell” cars work similarly to the electric vehicles we see today, except that instead of needing to be charged, they produce electricity while on the go. For a discussion of how fuel cell vehicles generate electricity, see the 2023 spring Sierran issue: bit.ly/3OfJRGl
While hydrogen-powered cars seem innovative and one of the many solutions to our climate change problems, they cost more than comparable-sized conventional cars. Suitable storage of hydrogen is one of the key cost factors.
Nanotech’s Emerging Role for Storing Hydrogen Cheaply and Safely
Hydrogen vehicles offer shorter refueling times and longer ranges than EVs. Most manufacturers have opted for high-pressure storage of hydrogen. This is not only costly but also unsafe. Researchers are working on solving this problem by using material organic frameworks (MOFs). It is believed that MOFs can be developed to store hydrogen in much the same way that a sponge can absorb and hold water.
Scientists have demonstrated that highly porous MOFs can hold large amounts of hydrogen at low pressure, which in fuel cell vehicles could be a safer and cheaper alternative than high-pressure, space-consuming hydrogen tanks. Hydrogen can be “adsorbed” onto the surfaces of porous solid materials for high storage density at low pressures. These materials must meet criteria for fast charging (fills) and discharging (flow) of hydrogen, and the hydrogen must flow at a rate that is suitable for the temperature and pressure ranges of fuel cell operation. They must also last the operational lifetime of the fuel cell vehicle.
In 2020, a research team at Northwestern University reported finding an MOF that fulfills volumetric (size) and gravimetric (mass) requirements criteria: NU-1501-A, which they said has minute pore sizes that are ideal for hydrogen storage at low pressure and exceed Department of Energy specifications for workable hydrogen MOFs.
Conclusion
Hydrogen-powered cars are a promising green alternative to gasoline, as greenhouse gas emissions are zero if green hydrogen is used. To work toward 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 (refueling stations) so that these cars can get the needed hydrogen on the road. Overall, while MOFs do still need further development, they unlock a new path for hydrogen-powered car development.
Resources
Northwestern Discovery: bit.ly/3MebFIF
Department of Energy Hydrogen Report: bit.ly/3OiM9EJ