What’s the role of hydrogen in the future of energy?
Hydrogen is some kind of ever lasting promise. It has been being mentioned as the future of energy for almost three decades, but we are still waiting for it. It is not the time that lacked: during this years, we have seen the rise of batteries as superior devices for energy accumulation, and of photovoltaic panels as one of the most reliable renewable energy sources.
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Obviously to say, there are some serious issues that impeded a real hydrogen revolution. But they come with a lot of opportunities as well, so that we can be confident that in some years we will finally see the fulfilment of that promise. Maybe, in a quite different fashion than we expected.
Hydrogen is interesting as energy source because each molecule contains a lot of energy compared to its weight. Its exploitation needs only to combine it with oxygen, which is readily available in our atmosphere. As a result we obtain energy and water, a completely harmless chemical. Quite useful, if it weren’t for the total absence of molecular hydrogen on Earth. Hydrogen, as also helium, is simply too light to be kept by terrestrial gravity, and when in atmosphere it is dispersed to surrounding space. We can find hydrogen mainly in water, but extracting it requires at least the same amount of energy that can be obtained by it.
But some alternative sources of hydrogen are attracting attention.
The most fascinating one is mimicking plants. “(Photocatalytic) water splitting” and “artificial photosynthesis” are two ways to refer to the same thing: being able to produce hydrogen directly from sunlight, as it is done in leaves. This technology has been studied for years by the notorious Prof. Nocera, who succeeded in making an operating artificial leaf. But there are problems related to durability, because the device life is no more than a few hours. More realistically, realistically humanity will not be able to exploit artificial photosynthesis at an industrial level for many years.
Biomass is another solution for obtaining hydrogen: it is renewable, it is abundant, but we throw away most of it. In reality, hydrogen from biomass is silently entering our homes without anyone noticing. Biogas, that is the gas produced from biomass, is a renewable energy source that is being added to gas grids in increasing fractions, and contains hydrogen. This means that while our gas grids become more sustainable, we also use some hydrogen.
But it is possible to be more ambitious, always starting from biomass. Hydrogen can be obtained from it through fermentation, gasification, and some chemical processes that go under the name of reforming. Such hydrogen would be produced locally, because biomass plants tend to be relatively small and well spread over territories.
Even if we had a cheap and endless source of hydrogen, there would be other problems as:
Storage, hydrogen is gaseous and has a low energy density per volume unity (although higher than batteries)
Infrastructure for hydrogen shipping as storage is totally lacking, and would need huge investments
Hydrogen needs fuel cells to be consumed, that are expensive and not so diffused.
But there are ways to overcome these issues, as soon as we forget hydrogen as a primary energy source for the entire world and we shift to a local perspective.
The local perspective is very important, because is the only current solution for the lack on infrastructures. This is why hydrogen is being abandoned as a fuel for cars, but can become a thing for trucks and trains. The company that manages a train or truck fleet has enough resources to build its hydrogen production plant, that today would be probably an electrolyser fed by photovoltaics, and uses that hydrogen only for its vehicles. Prototypes of hydrogen trains, equipped with fuel cells, are already circulating in Germany.
Some solutions to ease hydrogen storage are under development. Several technologies have been proposed for this task, but none is already set to become dominant. A newcomer is worth mentioning: the so-called Metal Organic Frameworks. MOFs are an innovative class of materials with a regular structure and wide recurring porosities. Because of this, they boast tremendous surface areas, up to football fields per gram of material. Such materials, when they bond hydrogen on their surface, are able to accommodate much more molecules than gaseous hydrogen under pressure.
Hydrogen can be a bridging energy source, between the actual renewable source and the final use. It can act as a buffer: it is widely known that renewable energy production does not match usage, so we need a way to store energy from the moment it is produced until it is needed. This can be done with batteries, but the battery size would increase proportionally to the amount of energy, or using hydrogen. Reversible fuel cells are devices meant to do so: they can produce hydrogen from electricity and vice versa. Hydrogen is simply stored in tanks. These cells are still in development, but they can become protagonists in the future. In particular, the low efficiency shall be improved, as, currently, only half of the electrical energy can be obtained back from these cells.
One more final concept should be evidenced. Hydrogen is a chemical of fundamental importance today, because it is used for the production of ammonia in the Haber-Bosch process, a process that is so important that 1% of world energy is used for it. In this case, hydrogen comes from reforming of fossil fuels, with subsequent emission of greenhouse gases and pollution. There is no doubt that a renewable source for this hydrogen must be found, if we want to decarbonize our economy, and the same source will be probably used also to supply hydrogen for other purposes. Hence, the question is not whether hydrogen will be an energy source in the future, but how.
Andrea Bedon, PhD
Administrator | Efesto Innovation srl