What is hydrogen ?

What is hydrogen ?

Hydrogen is the most common element in the universe. That is the main component of gaseous planets and stars, but it is rarely found in free state on Earth.
Hydrogen bounds with other elements. With oxygen it forms water (H2O) and combined with carbon it produces hydrocarbon (CH4, C2H6, …).

Hydrogen atom is mostly combined with another hydrogen atom to create the “dihydrogen molecule” (H2). This one could be found on gas state or in a liquid state – represented by the acronym LH2 – by cooling the gas at -252.87°C.

Hydrogen is a natural element. It is an energy carrier and not a power source  itself. It is produced by extracting hydrogen molecule from other compounds, such as water.

Hydrogen is often called “green fuel”, because it can be produced without carbon emission by renewable energies, like solar panels and wind turbine thanks to the electrolysis process.
This process is becoming more and more important in the hydrogen production range, but, currently the lowest-cost option to produce hydrogen is still the natural gas reforming process.

Nevertheless, water electrolysis process is one of the solution studied to achieve energy transition. This process allows a local hydrogen production (see below), as energy carrier, hydrogen allows to store renewable energy peak production to use it later without carbon-emission.

How hydrogen is produced ?

The world of science debates of potential natural hydrogen sources in Russia and others places. Nevertheless these sources are not industrialized and two main methods are used to industrially produce hydrogen:

  • Water electrolysis: This process allows to separate elements of the water molecule by an electric current through a compound.
    The water molecule is composed of two elements, two hydrogen cations and one oxygen anion. An electromagnetic attraction between the ions allows the element to hold together to create the molecule.When the electric current flows between the electrodes the ions are attracted to the opposite charged electrode and the water molecule is split into Hydrogen and Oxygen.
    As a result, hydrogen gas and oxygen gas could be collected separately, Hydrogen cations gathered around the anode (negative electrode) and Oxygen anions coming together around the cathode (positive electrode).
  • Steam reforming: this hydrogen production process is based on the use of hydrocarbon gas, in which high temperature steam (700°C-1000°C) is used to produce hydrogen.
    The most common process is steam-methane reforming which consists of three main stages:
    Firstly, methane (CH4) is cleaned from Sulfur by a catalytic chemical process called hydrodesulphurization.
    In a secondary step, methane is mixed with steam to produce Hydrogen and Carbon Monoxide during the steam-methane reforming reaction. The Carbon Monoxide is combined again with water, during the water-gas shift reaction, to create Hydrogen and Carbon Dioxide.
    Lastly, during the final stage, Hydrogen and Carbon Dioxide are separated and removed from the gas steam.
    The reactions could be summed-up by the following equations:
    CH4 + 2 H2O → CO + 3 H2 + H2O → CO2 + 4 H2

What are the advantages of using hydrogen?

The H2 molecule of hydrogen (commonly known as hydrogen) consists of two hydrogen atoms. It presents an interesting energy density (per unit fuel mass) that can be exploited through technological and scientific research

  • Powerful and efficient: The hydrogen combustion generates a high amount of energy (which can be exploited to produce heat or electricity);.
  • No harmful emissions: Hydrogen can be produced by hydrolysis from green and renewable energy (wind, solar, hydraulic, …) which reduces greenhouse gas emissions.
  • Easy to carry and to store: Hydrogen could be stored as gas-state in bottle or in solid forms with metal hydrides. The hydrogen tanks can be stored easily.
  • Environmentally friendly: The hydrogen combustion is completely decarbonized.

What is the expected progress to be achieved to disseminate hydrogen?

Hydrogen technology has largely been developed during the last few years thanks to scientific and technological achievements. Nevertheless, there is still room for innovation and a lot of research efforts have been committed to overcome various barriers:

  • Hydrogen production requires a lot of energy, especially in electrolysis that ensures “green” hydrogen production ;
  • Its storage in large quantities is difficult due to its low density and requires a large amount of energy for its compression (high pressure gas cylinders), liquefaction or solid storage (metal hydrides) ;
  • The cost of carbon-free production process is high, and its use by the public requires the implementation of major investments ;
  • Hydrogen is a flammable gas and requires precautions during storage and use.

The widespread use of hydrogen requires working proactively on the hydrogen sector to improve technology, to increase efficiency and to embed hydrogen into existing technologies to make the most of its advantages.

Does hydrogen have its place within the energy transition?

Hydrogen was at the heart of the debate at COP 21 held in Paris in December 2015. The hydrogen will play an important role in the energy transition in addition to renewable energy.

Renewables are intermittent and may produce more energy by the time that the network can absorb or even do not produce enough energy to meet network demands.

This phenomenon is observed with photovoltaic solar panels that produce an energy surplus between 10h and 16h but do not cover a home’s needs in the morning or in the evening.

Hydrogen allows, in particular, to store surplus of energy due to intermittent energies as it overcomes the constraints of decentralized production and finally its use can significantly reduce emissions of greenhouse gases.

Hydrogen thus has a relevant role in the energy transition, though its industrial operation still requires a lot of investment.


How to use hydrogen?


As an energy carrier, hydrogen can be converted to electricity, heat or kinetic energy and can be used:

  • For stationary applications, through the production of electricity and/or heat in buildings (principle of combined heat and power production);
  • For industrial applications by using hydrogen as a chemical compound;
  • For mobile applications by using hydrogen as a driving force;

The conversion of hydrogen to electricity requires an energy converter: the hydrogen fuel cell (or fuel cell).