Hydrogen
proton-exchange membrane fuel cell that is used in vehicles due to a low operating temperature and relatively high-power density in comparison to other fuel cells.
The ways of producing hydrogen
Despite being the most abundant element in the universe, pure hydrogen is rarely found on earth. This means that it must be obtained from molecules containing hydrogen atoms such as water or methane, which requires the breaking of chemical bonds, making obtaining hydrogen an endothermic process requiring energy. It is for this reason that hydrogen is seen as an energy carrier rather than an energy source. One of the major challenges that restricts the viability of hydrogen energy is the initial production of hydrogen as it requires energy intensive processes which are expensive and put into question whether hydrogen energy really is sustainable.
Figure 3: the colour spectrum of hydrogen, from Acciona (2022) ‘ What are the colours of hydrogen and what do they mean?’
One of the main methods of obtaining hydrogen is steam-methane reforming. This endothermic process reacts methane with steam in the presence of a nickel catalyst to produce hydrogen and carbon monoxide. The carbon monoxide produced from this reaction is then reacted with steam to produce carbon dioxide and water in a water- gas shift reaction. This method produces ‘grey’ hydrogen . However, if the carbon dioxide emitted from this reaction is captured, it produces ‘blue’ hydrogen. Steam-methane reforming is currently the most common way of producing hydrogen due to its low cost but doesn’t provide a sustainable source of hydrogen due to the emission of approximately 8-10 kg of carbon dioxide per kg of hydrogen produced. 2
Steam-methane reforming reaction: 𝐶𝐻 4 + 𝐻 2 𝑂 →𝐶𝑂+ 𝐻 2 Water-gas shift reaction: 𝐶𝑂+ 𝐻 2 𝑂 →𝐶𝑂 2 +𝐻 2
A process called gasification can be used to obtain a synthesis gas from coal and biomass by reacting it with oxygen and steam at high temperatures. This synthesis gas contains a mixture of mainly hydrogen and carbon monoxide which is then reacted with steam to obtain hydrogen.
Electrolysis of water is another method of obtaining hydrogen. An electric current is used to separate hydrogen from oxygen in water and if the electricity comes from a sustainable source such as solar or wind, electrolysis of water can provide a carbon-free source of hydrogen. However, the electrolysis of
2 Hydrogen Newsletter https://www.hydrogennewsletter.com/gh2-facts.
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