Hydrogen present and future. Part 2

If the reader has previously been very interested in learning about the development and current applications of hydrogen, he or she will certainly, and perhaps surprisingly, have been confronted with the curious fact that it is usually mentioned with a “surname” that designates its color. Thus, although hydrogen, as a chemical element, is logically unique – it is the first in the periodic table and its atom consists of one proton and one electron – it is repeatedly referred to as hydrogen, blue, gray, turquoise, yellow….

This chromatic scale is not capricious, but a convention that makes it possible to identify the origin of the energy used in the generation of hydrogen and to indicate whether systems for the capture and storage (CCS) of the CO₂ produced are used. In other words, the assignment of colors is a way of illustrating the greenhouse gas (GHG) emissions associated in each case with the hydrogen production processes.

At present, grey hydrogen is the most abundant, but blue and green hydrogen have the most promising future in view of current technological developments. 

Grey hydrogen is obtained from natural gas, i.e. it has its origin in fossil fuels, so its production generates CO₂ (in fact, it is the main source of CO₂ in a refinery). Blue hydrogen has the same origin as grey hydrogen, but includes the capture of a large part of the CO₂ emitted in the process. In turn, green hydrogen is produced by electrolysis of water, so the electricity consumed in its production process is of renewable origin; in other words, its generation does not emit CO₂ at any link in the production chain.  

 In any case, the important thing to remember is that, although the resulting hydrogen is unique – by the way, the chemical element most present in nature and one of the cleanest and most efficient fuels in existence, if not the most-, different technologies can be used to produce it. 

The key, therefore, is to have different technological developments that enable the reduction of emissions in the various existing carbon-intensive installations and to promote new installations, also of different types, that are low-intensity or carbon-neutral.

In fact, it is likely that all these different technologies will have a place on the energy map of the immediate future and, therefore, the “different colors” of hydrogen will coexist in the coming decades in a complementary way. If anything, it is safe to assume that blue hydrogen will play a very important role in the energy transition process, as an intermediate and affordable step towards reducing the carbon footprint, until the mass production of green hydrogen is achieved.

Although significant and accelerated steps are being taken, the last goal – large-scale production of green hydrogen – currently faces significant technological challenges that need to be overcome to increase the efficiency of the equipment that generates it. 

At present, it can be estimated that this equipment -the electrolyzers- has an average efficiency of around 60%, although projects are already underway to develop high-temperature electrolyzers that should enable a substantial increase in this percentage. In any case, although electrolysis technology is already viable for certain applications: mobility, power generation for buildings, support for investments in renewables, hydrogen production in places where carbon capture and storage is not possible, etc., it will require a certain amount of time and effort to mature economically and reach the necessary scale factors required by the market. 

Specifically, the technology for green hydrogen production by water electrolysis is currently most developed in alkaline electrolysis, i.e. using an alkaline medium. However, PEM (Proton Exchange Membrane) technology has come a long way in recent years and can now compete with alkaline electrolysis, depending on the characteristics and capacity of each particular hydrogen production plant. 

In addition to these two technologies, there is also AEM (Anionic Exchange Membrane), which combines the advantages of alkaline with those of PEM, and SOEC (Solid Oxide Electrolyzer Cell), for which better yields are expected, but which is still under development and cannot be applied on an industrial scale for the time being.

Alkaline electrolysis and PEM can be considered fully developed from a technological point of view; the objective now in relation to them is to improve their efficiency and reduce their production costs. As for AEM, it will have the potential to replace alkaline and PEM in the not too distant future if the cost reductions expected to be achieved with it are finally confirmed. On the other hand, SOEC technology is still some time away from becoming a reality on an industrial scale. 

In contrast, the technology for CO₂ capture in gray hydrogen installations is currently a more mature, more accessible and more economically competitive technology.

However, it must be stressed that many efforts are being made to shorten the time required for the maturation of these technological developments, especially through strategic alliances between leading national and international companies, which were unthinkable until very recently. 

Therefore, the interested reader will have seen that many of the hydrogen projects that are publicly reported are being addressed through the collaboration of several companies, an effort in which Técnicas Reunidas is particularly active.

In short, there are currently various technological solutions for producing hydrogen that have different degrees of maturity, scale and economic viability, but which in several cases are already being applied in practice. 

These are different technologies that may be more or less useful depending on various factors: their time of use, their development and efficiency, their reliability and performance, the type of end use of the hydrogen generated… In any case, it seems beyond any doubt that progress in this field will give a strong boost to the large-scale availability of a clean and sustainable energy source.