Hydrogen, microbiology and its perspectives.

5 questions to Martina Cascone, PhD student interested in studying the microbiology of underground hydrogen storage sites and natural hydrogen seeps.

Featured image

Martina Cascone, a PhD student in biotechnology at the University of Naples Federico II at the Giovannelli Lab, studies hydrogen storage with a focus in microbiology. Her research combines fieldwork, laboratory analysis and bioinformatics with a look towards the business approach, thus allowing her to have a large- and small-scale view.

Your PhD is based on the search for natural hydrogen sources and potential hydrogen storage sites. Why study this gas? What are the applications? To understand why there is such a great interest in hydrogen gas, we need to consider the current climate change on our Planet. The Earth is warming, CO2 concentrations in the atmosphere are reaching the highest levels ever in human history, and this is happening incredibly fast. To slow down this railroading process, our society’s energy budget is also relying on Renewable Energy Sources such as solar, hydropower, wind and geothermal sources. They are all very useful but share an important limitation: the intermittency. For instance, solar energy production depends on sunlight, which is not constant throughout the day due to factors like cloud cover and nightfall. Similarly, wind power generation relies on the availability and strength of wind, which can fluctuate. The intermittency of these renewable energy sources poses a challenge for maintaining a stable and reliable power supply. They can not be stored and used when there is a peak energy demand, so it happen to produce a lot of energy that soon becomes unutilized and wasted. This is where H2 turns out to be the key to the problem: this surplus energy can be used to convert water in H2 and O2, through specific instruments called “electrolyzers”. H2 carries the energy surplus (that is why it is called an energy carrier) and will be able to release this same energy again, coming in contact with O2. This reaction produces water as the final product, being completely green and not releasing greenhouse gasses into the atmosphere. In addition to being entirely sustainable, this gas can be used not only on a small scale such as domestic use (as it happens for Renewable Energy Sources) but also at a large scale: this would represent a concrete revolution for the entire energy sector. Alt text Hydrogen is defined as an “energy vector” and not as a direct energy source, why? Hydrogen can be defined as an energy carrier because it stores energy and enables its transport and distribution. As I mentioned before, H2 “carries” energy when it is the product of artificial reactions such as electrolysis, made through the use of external energy, in this case corresponding to the surplus energy produced by the different Renewable Energy Sources (RES). The power of this vector lies in allowing the utilization of the surplus energy for future necessities on a small and large scale, completely in sync with society’s energy demand. It is worthwhile to clarify that H2 is also a natural energy source because it is already present on our planet and we know of several geothermal seeps where it is naturally released. Recent studies have shown that the estimated planetary H2 amount is enormous, although we still have not been able to discover it in its entirety. In particular, in the paper entitled “Hidden Hydrogen” published in the journal Science, Eric Hand affirms: “There might be enough natural hydrogen to meet burgeoning global demand for thousands of years”. This could be an outstanding discovery because H2 could become the first existing energy source to be both natural and renewable, and to be exploited without big negative effects on the Earth’s climate. Alt text What are the advantages and what are the critical issues of hydrogen storage? One of the main advantages is that H2 is easy to be produced artificially, it can be a natural and renewable resource present on our planet in important quantities and it can be widely used on small to large scale. Compared to the other RES, H2 can be continuously available and in sync with society’s peak energy demand. On the other hand, all that glitter is not gold: H2 is highly inflammable, and due to its small size it is also highly volatile. To overcome these two problems, the so-called Underground Hydrogen Storage seems to be the best solution, because H2 can be safely protected from the atmospheric O2 and also from potential terrorist attacks and at the same time it can be properly trapped in the rock pores. The more studied underground environments for this purpose are aquifers, salt caverns and natural gas/oil porous reservoirs. Particular interest is addressed to the latter for medium and long-term hydrogen storage solutions because of the presence of existing infrastructures that could be re-utilized for hydrogen injection and recovery cycles. This strategy makes hydrogen usable with the times and methods already developed for natural gas, ensuring high safety and versatility in energy production. Unfortunately, the problems to solve do not end here: hydrogen is a powerful microbial electron donor and this means that when it’s stored underground, microbes could be able to use and consume it, negatively affecting the entire H2 storage technology. Since knowledge about subsurface microbial physiology is still scarce, one way I’m adopting to implement it is by studying microbes that inhabit natural hydrogen seeps, where this gas is constantly present and becomes an electron donor for a range of metabolic activities. This zoom-in in the microbiology of the underground will also enable me to have an insight into the possible responses of the potential storage sites’ microbial community to the artificial hydrogen injection and to develop ad hoc mitigation strategies to optimize this technology.

What role does microbiology play in this sector? Is it an area that requires a certain multidisciplinarity? Microorganisms are fundamental in this field because even if the geological setting of a selected site seems to be greatly suitable for gas storage, microbes could change the whole story, consuming hydrogen and releasing dangerous by-products. Indeed, among the known hydrogenotrophic microbes, literally “microbes that eat hydrogen”, there is a good part able to use SO42- as an electron acceptor. This metabolism leads to the production of compounds such as H2S, which besides being inflammable is also corrosive to the Underground Hydrogen Storage infrastructures. This latter scenario is something that the energy companies wish to avoid, but to understand the probability of it happening, it’s necessary to have a consolidated multidisciplinary approach. It is thus opportune to study different focal features of potential hydrogen storage environments, such as their geology, including porosity, permeability, stratigraphy and mineral composition; their geochemistry, shaped by which and how many ions, organic and inorganic compounds and trace metals are detected in the fluid phase, and which type of gasses and in which composition they are present in the storage site head-space. Finally, it’s important to measure their physico-chemical factors such as temperature, pH, salinity, depth, pressure and the total area available to be occupied by the injected gas. Just as an example: discovering a certain abundance of sulfate and organic matter, could lead to hypothesising the presence of a quite active heterotrophic microbial community. This is not only potentially able to release sulfide but also, growing fast, to create biofilms inside the rock pores, clogging them and affecting the final storage space capacity of the site. The assessment is not so trivial, because even just the fluctuation of one parameter could change the occurring scenario: everything revolves around thermodynamics rules.

What do you think will be the future developments in this area? I know that science is rapidly advancing in this field and I strongly believe that, implementing the knowledge about it, we will soon be able to select and monitor hydrogen reservoirs in different areas of our planet. With the actual encouraging premises, the possibility that, in the not-too-distant future, hydrogen gas will become the first green energy source sustaining the entire world society, is not to be underestimated. Alt text Fotos: Jacopo Pasotti, 2023