Hydrogen cars

Hydrogen cars as they sound uses hydrogen as a fuel to power up. Hydrogen which is the most abundant material in the universe appears to have potential to full fill our energy needs of cars and it has but it doesn't present in the form of gas on earth and available only in the combined form also we don't have any engine for its combustion in cars and harness its full power instead we are using it for generating electricity from fuel cells and ends up generating less power than a combustion process can generate.

We are using hydrogen as a fuel in rockets for generating thrust to escape earth's gravity by direct combusting it since 1970. I hope in the near future we also use this technology in our cars and stop polluting our nature as it only generates heat and water as its product.

I think I have already described the whole idea of how we are using hydrogen in our world and also you have got an idea of how a hydrogen car works.

So let's see How Hydrogen cars work and why it is not popular as compared to electric cars.

HOW HYDROGEN CARS WORKS?

Hydrogen cars use hydrogen as a fuel which combines with oxygen inside a fuel cell to generates electricity which rotates the electric motor to drive Hydrogen cars.

This whole process sounds simple but it is actually complicated let's dig a little bit deep to taste the actual process.

• At the beginning of process hydrogen in the form of gas is filled in the fuel tank which then transferred to a fuel cell.
• In the fuel cell, hydrogen acts as an anode where it loses its electron which in turn generates electricity for driving the electric motor and move towards the cathode.
• At the cathode, we input oxygen which by combining with hydrogen cations coming from the anode through proton exchange membrane and electrons and produce water.
• Proton exchange membrane is a type of membrane which only allow to positively charged ions to pass through them.
• Now we are getting a DC current from the fuel cell but to drive an electric motor we need to convert it in AC. So we need an inverter for that purpose.

Advantages over Battery-Powered Cars

• Hydrogen is very light in nature and compressed hydrogen has a capacity of 40000 Wh/kg as compared to lithium-ion batteries having a capacity of 278 Wh/kg.
• Due to the lightweight and more capacity, it can power the car for a long-range of distance.
• For battery-powered cars increasing the range of miles required to add more batteries which in turn increase the weight of the car. Hence vehicle heavy brakes and other structural features which limits its production after a certain range of miles.
• For hydrogen cars, this not an issue a few fuel cells run as long as the hydrogen is present in the fuel tank. Hence a limited amount of fuel cells can do the job and both fuel cells and hydrogen is not that much heavy. 
• It takes only 5 minutes to refill a hydrogen tank and battery-powered cars take lots of time in charging them.

Hydrogen has great advantages over batteries but why they are not so popular, let's have a look over on real-world example.

Tesla Model - 3 

It takes $10-12 to get fully charge a 75 kWh battery and can be driven for a range 500 km in a single charge and hence it cost 2.24 cents for 1 km.

Toyota Mirai

It takes hydrogen as a fuel and cost $85 for approx 480 km and hence 17.7 cents per km.

• Now we can clearly see why electric vehicles are more in demand than hydrogen one.
• The reason is the cost of production of hydrogen even it has the above advantages over electric vehicles.

Why hydrogen have high production cost?

This question's answer includes two reasons, one is hidden in the way how hydrogen is produced and second is how it is stored. Let's have a look at the first reason.

Ways to produce hydrogen

• Steam- Methane reforming reaction

CH₄ + H₂O + HEAT → CO + 3H₂

• By electrolysis

2OH^- → 2e^- + 1/2O₂ + H₂O

2e- + 2H₂O → H₂ + 2OH-

Here electricity can be provided using renewable resources like solar energy but it gets reduced by 30% before electrolysis even start.

• Proton Exchange Membrane

H₂O → 2H⁺ + 1/2O₂ + 2e^-

2H⁺ + 2e^- → H₂

This is the best method to produce hydrogen as by this method we can produce hydrogen on the site and has an efficiency of 80% which is more than any other method.

The second reason is its storage

• This happens due to the very low density of hydrogen and so for storage purpose, we need big containers to store but before storing it we have to compress it 790 times more than 1atm.
• This compression requires lots of energy and has an efficiency of 87% and hence this method is not the preferred one.
• Don't worry we have an alternative in which we do not compress it rather we convert it into liquid cryogenically in which we reduce the temperature of hydrogen to -252.9 degree Celcius.
• Liquid hydrogen is easy to store as the size of the tank to store it is smaller than the tank to store compressed hydrogen.
• Liquid hydrogen tank is easy to install on-site as it occupies less space.
• But it also consumes 40% energy stored inside the hydrogen.
• So compressing hydrogen and storing it is a better way to store hydrogen.

• Assuming that we are producing and storing hydrogen by the best way we lost 20% energy in PEM in which electricity is coming from renewable sources and 13% percent in storing it so we have a total loss of 33%. 
• On the other hand in charging a battery we just loose 6% energy in total i.e 5% grid loss and 1% in charging the batteries.

Losses during power supply from the fuel tank to wheels

• Now the hydrogen is in the tank, we have to generate electricity from it to drive the vehicle. For this, we again use PEM Fuel cell but in reverse in which we pass hydrogen it separates the hydrogen ion from electron and these electrons generate electricity. This works with 60% efficiency.
• On the other hand for charging a battery from an AC current, we need a charger which efficiency of 92% and these batteries have leakage problem which again reduces the efficiency by 10%. After this to run an electric motor we need an inverter to convert DC current into AC which has efficiency of 90%.
• In the same way, electricity generated from the hydrogen fuel cell is DC so we need an inverter to convert DC to AC to power motor.
• Now considering motor losses which are 95% efficient we have total efficiency of a hydrogen vehicle is 1/2 the efficiency of electric vehicles.

This is the reason for not using hydrogen-powered vehicles and why we prefer electric vehicles even hydrogen is more in abundance and is more powerful than electric vehicles.

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