Saturday, November 6, 2021

What is the hydrogen fuel?

Hydrogen fuel is a zero-carbon fuel burned with oxygen; provided it is created in a zero-carbon way. It can be used in fuel cells or internal combustion engines.

Regarding hydrogen vehicles, hydrogen has begun to be used in commercial fuel cell vehicles, such as passenger cars, and has been used in fuel cell buses for many years. It is also used as a fuel for spacecraft propulsion.
Because pure hydrogen does not occur naturally on Earth in large quantities, it usually requires a primary energy input to produce on an industrial scale. Hydrogen fuel can be produced from methane or by electrolysis of water.

As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming or partial oxidation of methane and coal gasification with only a small quantity by other routes such as biomass gasification or electrolysis of water.

Steam-methane reforming, the current leading technology for producing hydrogen in large quantities, extracts hydrogen from methane.

However, this reaction releases fossil carbon dioxide and carbon monoxide into the atmosphere which is greenhouse gases exogenous to the natural carbon cycle, and thus contribute to climate change.

In electrolysis, electricity is run through water to separate the hydrogen and oxygen atoms. This method can use wind, solar, geothermal, hydro, fossil fuels, biomass, nuclear, and many other energy sources.

Hydrogen is found in the first group and the first period in the periodic table, i.e. it is the lightest and first element of all. Since the weight of hydrogen is less than air, it rises in the atmosphere and is therefore rarely found in its pure form, H2.

In a flame of pure hydrogen gas, burning in air, the hydrogen (H2) reacts with oxygen (O2) to form water (H2O) and releases energy.

If carried out in atmospheric air instead of pure oxygen, as is usually the case, hydrogen combustion may yield small amounts of nitrogen oxides, along with the water vapor.

The energy released enables hydrogen to act as a fuel. In an electrochemical cell, that energy can be used with relatively high efficiency. If it is used simply for heat, the usual thermodynamics limits on the thermal efficiency apply.

Although hydrogen has a high energy content per unit mass, at room temperature and atmospheric pressure it has a very low energy content per unit volume, compared to liquid fuels or even to natural gas. For this reason, it is usually either compressed or liquefied by lowering its temperature to less than 33 K.

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