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The Engineering Behind Hydrogen-Powered Cars

By Mark G. McLaughlin

There are many reasons why someone would consider driving or buying a hydrogen fuel cell vehicle, such as the Toyota Mirai. The earth will eventually run out of fossil fuels, and as it does the cost of the gasoline and diesel fuel that burns in internal combustion engines will rise. Hydrogen fuel cells, however, run on a gas that is found in water – a substance which covers three-fourths of the earth's surface. Hydrogen fuel cell vehicles are thus likely to someday eclipse and eventually replace those that run on petroleum products. Hydrogen-powered cars are also more efficient, and better for the environment – as they do not pollute.

How a hydrogen fuel cell works

Automobiles with hydrogen fuel cells run on electricity. That electricity is generated when a fuel made up of hydrogen and oxygen react in a chamber. The hydrogen enters at one anode (known as the electrode) and oxygen enters at the other anode (the cathode). The chemical reaction of hydrogen and oxygen produces an electric current. (It also produces water, which must be drained from the cell, or steam.) The electrically-charged particles are carried from one anode to the other by an electrolyte. This electric current powers a battery; a stack of such batteries powers an electric motor.

Different types of fuel cells

There are several different types of fuel cells. Alkali cells use compressed hydrogen and oxygen with potassium hydroxide as the electrolyte. Molten carbonate fuel cells use high-temperature compounds of sodium or magnesium carbonate as the electrolyte. Phosphoric Acid cells use that material as the electrolyte. Solid Oxide cells use a ceramic compound of metal oxides as the catalyst. Proton Exchange cells use a thin polymer sheet as the electrode. This last type is the one preferred by many automobile makers, including Toyota, which uses that technology in its Mirai.

Advantages of hydrogen-fuel cells: no pollution, higher efficiency, cheap and endless fuel source

Unlike in an internal combustion engine, in a fuel cell, there is no combustion – nothing is burned. The emissions from an internal combustion engine are a pollutant. The only by-product of a hydrogen fuel cell is water – in the form of a liquid or as steam. Hydrogen-powered vehicles are also much quieter – almost completely silent – thus they do not produce the noise pollution of internal combustion engines. Hydrogen fuel cells are also more efficient at extracting energy than engines fueled by gasoline or diesel fuel. Hydrogen, moreover, is found in water, which covers three-fourths of the earth's service.

Why hydrogen-powered vehicles cost so much – and why prices are going down

Gearing up a factory to produce hydrogen-powered vehicles takes time and money. Converting other factories and garages and fueling stations from servicing internal combustion engines to hydrogen engines also takes time and money. As more such factories are built or retooled, more such vehicles will be produced, and with such quantity comes a reduction in costs to build – and prices at which to sell these cars. Toyota, for example, as of December 2017, has sold 5,300 of its hydrogen cell fueled Mirai model – about half of them in the U.S. market. The vehicle made its commercial debut in 2014 and sells for around $60,000.

The Mirai, Toyota's hydrogen fuel cell vehicle

The Toyota Mirai is that company's premier hydrogen fuel cell vehicle. It is powered by a polymer electrolyte fuel cell. The Mirai has a stack of 370 cells. The electricity from those cells goes to a nickel-metal hydride battery, which provides power to a 113 kilowatt (152 horsepower) engine. It has a range of 312 miles (500 km) between fill-ups; that translates to 66 mpg. Toyota is currently offering a package with three years of complimentary fill-ups, up to a value of $15,000. This four-door sedan is classed as a mid-size luxury car.


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